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1−1−1Navigation Aids

Chapter 1. Air Navigation

Section 1. Navigation Aids

1−1−1. General

a. Various types of air navigation aids are in usetoday, each serving a special purpose. These aids havevaried owners and operators, namely: the FederalAviation Administration (FAA), the military ser-vices, private organizations, individual states andforeign governments. The FAA has the statutoryauthority to establish, operate, maintain air naviga-tion facilities and to prescribe standards for theoperation of any of these aids which are used forinstrument flight in federally controlled airspace.These aids are tabulated in the Chart Supplement U.S.

b. Pilots should be aware of the possibility ofmomentary erroneous indications on cockpit displayswhen the primary signal generator for a ground−based navigational transmitter (for example, aglideslope, VOR, or nondirectional beacon) isinoperative. Pilots should disregard any navigationindication, regardless of its apparent validity, if theparticular transmitter was identified by NOTAM orotherwise as unusable or inoperative.

1−1−2. Nondirectional Radio Beacon (NDB)

a. A low or medium frequency radio beacontransmits nondirectional signals whereby the pilot ofan aircraft properly equipped can determine bearingsand “home” on the station. These facilities normallyoperate in a frequency band of 190 to 535 kilohertz(kHz), according to ICAO Annex 10 the frequencyrange for NDBs is between 190 and 1750 kHz, andtransmit a continuous carrier with either 400 or1020 hertz (Hz) modulation. All radio beaconsexcept the compass locators transmit a continuousthree−letter identification in code except during voicetransmissions.

b. When a radio beacon is used in conjunction withthe Instrument Landing System markers, it is calleda Compass Locator.

c. Voice transmissions are made on radio beaconsunless the letter “W” (without voice) is included inthe class designator (HW).

d. Radio beacons are subject to disturbances thatmay result in erroneous bearing information. Suchdisturbances result from such factors as lightning,precipitation static, etc. At night, radio beacons arevulnerable to interference from distant stations.Nearly all disturbances which affect the AutomaticDirection Finder (ADF) bearing also affect thefacility’s identification. Noisy identification usuallyoccurs when the ADF needle is erratic. Voice, musicor erroneous identification may be heard when asteady false bearing is being displayed. Since ADFreceivers do not have a “flag” to warn the pilot whenerroneous bearing information is being displayed, thepilot should continuously monitor the NDB’sidentification.

1−1−3. VHF Omni−directional Range (VOR)

a. VORs operate within the 108.0 to 117.95 MHzfrequency band and have a power output necessary toprovide coverage within their assigned operationalservice volume. They are subject to line−of−sightrestrictions, and the range varies proportionally to thealtitude of the receiving equipment.

NOTE−Normal service ranges for the various classes of VORs aregiven in Navigational Aid (NAVAID) Service Volumes,Paragraph 1−1−8.

b. Most VORs are equipped for voice transmis-sion on the VOR frequency. VORs without voicecapability are indicated by the letter “W” (withoutvoice) included in the class designator (VORW).

c. The only positive method of identifying a VORis by its Morse Code identification or by the recordedautomatic voice identification which is alwaysindicated by use of the word “VOR” following therange’s name. Reliance on determining the identifica-tion of an omnirange should never be placed onlistening to voice transmissions by the Flight ServiceStation (FSS) (or approach control facility) involved.Many FSSs remotely operate several omnirangeswith different names. In some cases, none of theVORs have the name of the “parent” FSS. Duringperiods of maintenance, the facility may radiate aT−E−S−T code (- � �� -) or the code may be

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1−1−2 Navigation Aids

removed. Some VOR equipment decodes theidentifier and displays it to the pilot for verificationto charts, while other equipment simply displays theexpected identifier from a database to aid inverification to the audio tones. You should be familiarwith your equipment and use it appropriately. If yourequipment automatically decodes the identifier, it isnot necessary to listen to the audio identification.

d. Voice identification has been added to numer-ous VORs. The transmission consists of a voiceannouncement, “AIRVILLE VOR” alternating withthe usual Morse Code identification.

e. The effectiveness of the VOR depends uponproper use and adjustment of both ground andairborne equipment.

1. Accuracy. The accuracy of course align-ment of the VOR is excellent, being generally plus orminus 1 degree.

2. Roughness. On some VORs, minor courseroughness may be observed, evidenced by courseneedle or brief flag alarm activity (some receivers aremore susceptible to these irregularities than others).At a few stations, usually in mountainous terrain, thepilot may occasionally observe a brief course needleoscillation, similar to the indication of “approachingstation.” Pilots flying over unfamiliar routes arecautioned to be on the alert for these vagaries, and inparticular, to use the “to/from” indicator to determinepositive station passage.

(a) Certain propeller revolutions per minute(RPM) settings or helicopter rotor speeds can causethe VOR Course Deviation Indicator to fluctuate asmuch as plus or minus six degrees. Slight changes tothe RPM setting will normally smooth out thisroughness. Pilots are urged to check for thismodulation phenomenon prior to reporting a VORstation or aircraft equipment for unsatisfactoryoperation.

f. The VOR Minimum Operational Network(MON). As flight procedures and route structurebased on VORs are gradually being replaced withPerformance−Based Navigation (PBN) procedures,the FAA is removing selected VORs from service.PBN procedures are primarily enabled by GPS and itsaugmentation systems, collectively referred to asGlobal Navigation Satellite System (GNSS). Aircraftthat carry DME/DME equipment can also use RNAVwhich provides a backup to continue flying PBN

during a GNSS disruption. For those aircraft that donot carry DME/DME, the FAA is retaining a limitednetwork of VORs, called the VOR MON, to providea basic conventional navigation service for operatorsto use if GNSS becomes unavailable. During a GNSSdisruption, the MON will enable aircraft to navigatethrough the affected area or to a safe landing at aMON airport without reliance on GNSS. Navigationusing the MON will not be as efficient as the newPBN route structure, but use of the MON will providenearly continuous VOR signal coverage at 5,000 feetAGL across the NAS, outside of the Western U.S.Mountainous Area (WUSMA).

NOTE−There is no plan to change the NAVAID and route structurein the WUSMA.

The VOR MON has been retained principally for IFRaircraft that are not equipped with DME/DMEavionics. However, VFR aircraft may use the MONas desired. Aircraft equipped with DME/DMEnavigation systems would, in most cases, useDME/DME to continue flight using RNAV to theirdestination. However, these aircraft may, of course,use the MON.

1. Distance to a MON airport. The VOR MONwill ensure that regardless of an aircraft’s position inthe contiguous United States (CONUS), a MONairport (equipped with legacy ILS or VORapproaches) will be within 100 nautical miles. Theseairports are referred to as “MON airports” and willhave an ILS approach or a VOR approach if an ILSis not available. VORs to support these approacheswill be retained in the VOR MON. MON airports arecharted on low−altitude en route charts and arecontained in the Chart Supplement U.S. and otherappropriate publications.

NOTE−Any suitable airport can be used to land in the event of aVOR outage. For example, an airport with a DME−re-quired ILS approach may be available and could be usedby aircraft that are equipped with DME. The intent of theMON airport is to provide an approach that can be used byaircraft without ADF or DME when radar may not beavailable.

2. Navigating to an airport. The VOR MONwill retain sufficient VORs and increase VOR servicevolume to ensure that pilots will have nearlycontinuous signal reception of a VOR when flying at5,000 feet AGL. A key concept of the MON is toensure that an aircraft will always be within 100 NM

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of an airport with an instrument approach that is notdependent on GPS. (See paragraph 1−1−8.) If thepilot encounters a GPS outage, the pilot will be ableto proceed via VOR−to−VOR navigation at5,000 feet AGL through the GPS outage area or to asafe landing at a MON airport or another suitableairport, as appropriate. Nearly all VORs inside of theWUSMA and outside the CONUS are being retained.In these areas, pilots use the existing (Victor and Jet)route structure and VORs to proceed through a GPSoutage or to a landing.

3. Using the VOR MON.

(a) In the case of a planned GPS outage (forexample, one that is in a published NOTAM), pilotsmay plan to fly through the outage using the MON asappropriate and as cleared by ATC. Similarly, aircraftnot equipped with GPS may plan to fly and land usingthe MON, as appropriate and as cleared by ATC.

NOTE−In many cases, flying using the MON may involve a morecircuitous route than flying GPS−enabled RNAV.

(b) In the case of an unscheduled GPS outage,pilots and ATC will need to coordinate the bestoutcome for all aircraft. It is possible that a GPSoutage could be disruptive, causing high workloadand demand for ATC service. Generally, the VORMON concept will enable pilots to navigate throughthe GPS outage or land at a MON airport or at anotherairport that may have an appropriate approach or maybe in visual conditions.

(1) The VOR MON is a reversionaryservice provided by the FAA for use by aircraft thatare unable to continue RNAV during a GPSdisruption. The FAA has not mandated that preflightor inflight planning include provisions for GPS− orWAAS−equipped aircraft to carry sufficient fuel toproceed to a MON airport in case of an unforeseenGPS outage. Specifically, flying to a MON airport asa filed alternate will not be explicitly required. Ofcourse, consideration for the possibility of a GPSoutage is prudent during flight planning as ismaintaining proficiency with VOR navigation.

(2) Also, in case of a GPS outage, pilotsmay coordinate with ATC and elect to continuethrough the outage or land. The VOR MON isdesigned to ensure that an aircraft is within 100 NMof an airport, but pilots may decide to proceed to anyappropriate airport where a landing can be made.

WAAS users flying under Part 91 are not required tocarry VOR avionics. These users do not have theability or requirement to use the VOR MON. Prudentflight planning, by these WAAS−only aircraft, shouldconsider the possibility of a GPS outage.

NOTE−The FAA recognizes that non−GPS−based approaches willbe reduced when VORs are eliminated, and that mostairports with an instrument approach may only have GPS−or WAAS−based approaches. Pilots flying GPS− orWAAS−equipped aircraft that also have VOR/ILS avionicsshould be diligent to maintain proficiency in VOR and ILSapproaches in the event of a GPS outage.

1−1−4. VOR Receiver Check

a. The FAA VOR test facility (VOT) transmits atest signal which provides users a convenient meansto determine the operational status and accuracy of aVOR receiver while on the ground where a VOT islocated. The airborne use of VOT is permitted;however, its use is strictly limited to thoseareas/altitudes specifically authorized in the ChartSupplement U.S. or appropriate supplement.

b. To use the VOT service, tune in the VOTfrequency on your VOR receiver. With the CourseDeviation Indicator (CDI) centered, the omni−bear-ing selector should read 0 degrees with the to/fromindication showing “from” or the omni−bearingselector should read 180 degrees with the to/fromindication showing “to.” Should the VOR receiveroperate an RMI (Radio Magnetic Indicator), it willindicate 180 degrees on any omni−bearing selector(OBS) setting. Two means of identification are used.One is a series of dots and the other is a continuoustone. Information concerning an individual test signalcan be obtained from the local FSS.

c. Periodic VOR receiver calibration is mostimportant. If a receiver’s Automatic Gain Control ormodulation circuit deteriorates, it is possible for it todisplay acceptable accuracy and sensitivity close intothe VOR or VOT and display out−of−tolerancereadings when located at greater distances whereweaker signal areas exist. The likelihood of thisdeterioration varies between receivers, and isgenerally considered a function of time. The bestassurance of having an accurate receiver is periodiccalibration. Yearly intervals are recommended atwhich time an authorized repair facility shouldrecalibrate the receiver to the manufacturer’sspecifications.

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d. Federal Aviation Regulations (14 CFR Sec-tion 91.171) provides for certain VOR equipmentaccuracy checks prior to flight under instrumentflight rules. To comply with this requirement and toensure satisfactory operation of the airborne system,the FAA has provided pilots with the following meansof checking VOR receiver accuracy:

1. VOT or a radiated test signal from anappropriately rated radio repair station.

2. Certified airborne check points.

3. Certified check points on the airport surface.

e. A radiated VOT from an appropriately ratedradio repair station serves the same purpose as anFAA VOR signal and the check is made in much thesame manner as a VOT with the followingdifferences:

1. The frequency normally approved by theFederal Communications Commission is108.0 MHz.

2. Repair stations are not permitted to radiate theVOR test signal continuously; consequently, theowner or operator must make arrangements with therepair station to have the test signal transmitted. Thisservice is not provided by all radio repair stations.The aircraft owner or operator must determine whichrepair station in the local area provides this service.A representative of the repair station must make anentry into the aircraft logbook or other permanentrecord certifying to the radial accuracy and the dateof transmission. The owner, operator or representat-ive of the repair station may accomplish the necessarychecks in the aircraft and make a logbook entrystating the results. It is necessary to verify which testradial is being transmitted and whether you shouldget a “to” or “from” indication.

f. Airborne and ground check points consist ofcertified radials that should be received at specificpoints on the airport surface or over specificlandmarks while airborne in the immediate vicinity ofthe airport.

1. Should an error in excess of plus or minus4 degrees be indicated through use of a ground check,or plus or minus 6 degrees using the airborne check,Instrument Flight Rules (IFR) flight must not beattempted without first correcting the source of theerror.

CAUTION−No correction other than the correction card figuressupplied by the manufacturer should be applied inmaking these VOR receiver checks.

2. Locations of airborne check points, groundcheck points and VOTs are published in the ChartSupplement U.S.

3. If a dual system VOR (units independent ofeach other except for the antenna) is installed in theaircraft, one system may be checked against the other.Turn both systems to the same VOR ground facilityand note the indicated bearing to that station. Themaximum permissible variations between the twoindicated bearings is 4 degrees.

1−1−5. Tactical Air Navigation (TACAN)

a. For reasons peculiar to military or navaloperations (unusual siting conditions, the pitchingand rolling of a naval vessel, etc.) the civilVOR/Distance Measuring Equipment (DME) systemof air navigation was considered unsuitable formilitary or naval use. A new navigational system,TACAN, was therefore developed by the military andnaval forces to more readily lend itself to military andnaval requirements. As a result, the FAA hasintegrated TACAN facilities with the civil VOR/DME program. Although the theoretical, or technicalprinciples of operation of TACAN equipment arequite different from those of VOR/DME facilities, theend result, as far as the navigating pilot is concerned,is the same. These integrated facilities are calledVORTACs.

b. TACAN ground equipment consists of either afixed or mobile transmitting unit. The airborne unit inconjunction with the ground unit reduces thetransmitted signal to a visual presentation of bothazimuth and distance information. TACAN is a pulsesystem and operates in the Ultrahigh Frequency(UHF) band of frequencies. Its use requires TACANairborne equipment and does not operate throughconventional VOR equipment.

1−1−6. VHF Omni−directionalRange/Tactical Air Navigation (VORTAC)

a. A VORTAC is a facility consisting of twocomponents, VOR and TACAN, which providesthree individual services: VOR azimuth, TACANazimuth and TACAN distance (DME) at one site.Although consisting of more than one component,

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incorporating more than one operating frequency,and using more than one antenna system, a VORTACis considered to be a unified navigational aid. Bothcomponents of a VORTAC are envisioned asoperating simultaneously and providing the threeservices at all times.

b. Transmitted signals of VOR and TACAN areeach identified by three−letter code transmission andare interlocked so that pilots using VOR azimuth withTACAN distance can be assured that both signalsbeing received are definitely from the same groundstation. The frequency channels of the VOR and theTACAN at each VORTAC facility are “paired” inaccordance with a national plan to simplify airborneoperation.

1−1−7. Distance Measuring Equipment(DME)

a. In the operation of DME, paired pulses at aspecific spacing are sent out from the aircraft (this isthe interrogation) and are received at the groundstation. The ground station (transponder) thentransmits paired pulses back to the aircraft at the samepulse spacing but on a different frequency. The timerequired for the round trip of this signal exchange ismeasured in the airborne DME unit and is translatedinto distance (nautical miles) from the aircraft to theground station.

b. Operating on the line−of−sight principle, DMEfurnishes distance information with a very highdegree of accuracy. Reliable signals may be receivedat distances up to 199 NM at line−of−sight altitudewith an accuracy of better than 1/2 mile or 3 percentof the distance, whichever is greater. Distanceinformation received from DME equipment isSLANT RANGE distance and not actual horizontaldistance.

c. Operating frequency range of a DME accordingto ICAO Annex 10 is from 960 MHz to 1215 MHz.Aircraft equipped with TACAN equipment willreceive distance information from a VORTACautomatically, while aircraft equipped with VORmust have a separate DME airborne unit.

d. VOR/DME, VORTAC, Instrument LandingSystem (ILS)/DME, and localizer (LOC)/DMEnavigation facilities established by the FAA providecourse and distance information from collocatedcomponents under a frequency pairing plan. Aircraft

receiving equipment which provides for automaticDME selection assures reception of azimuth anddistance information from a common source whendesignated VOR/DME, VORTAC, ILS/DME, andLOC/DME are selected.

e. Due to the limited number of availablefrequencies, assignment of paired frequencies isrequired for certain military noncollocated VOR andTACAN facilities which serve the same area butwhich may be separated by distances up to a fewmiles.

f. VOR/DME, VORTAC, ILS/DME, and LOC/DME facilities are identified by synchronizedidentifications which are transmitted on a time sharebasis. The VOR or localizer portion of the facility isidentified by a coded tone modulated at 1020 Hz ora combination of code and voice. The TACAN orDME is identified by a coded tone modulated at1350 Hz. The DME or TACAN coded identificationis transmitted one time for each three or four timesthat the VOR or localizer coded identification istransmitted. When either the VOR or the DME isinoperative, it is important to recognize whichidentifier is retained for the operative facility. Asingle coded identification with a repetition intervalof approximately 30 seconds indicates that the DMEis operative.

g. Aircraft equipment which provides for auto-matic DME selection assures reception of azimuthand distance information from a common sourcewhen designated VOR/DME, VORTAC and ILS/DME navigation facilities are selected. Pilots arecautioned to disregard any distance displays fromautomatically selected DME equipment when VORor ILS facilities, which do not have the DME featureinstalled, are being used for position determination.

1−1−8. Navigational Aid (NAVAID) ServiceVolumes

a. Most air navigation radio aids which providepositive course guidance have a designated standardservice volume (SSV). The SSV defines the receptionlimits of unrestricted NAVAIDs which are usable forrandom/unpublished route navigation.

b. A NAVAID will be classified as restricted if itdoes not conform to flight inspection signal strengthand course quality standards throughout thepublished SSV. However, the NAVAID should not beconsidered usable at altitudes below that which could

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be flown while operating under random route IFRconditions (14 CFR Section 91.177), even thoughthese altitudes may lie within the designated SSV.Service volume restrictions are first published inNotices to Airmen (NOTAMs) and then with thealphabetical listing of the NAVAIDs in the ChartSupplement U.S.

c. Standard Service Volume limitations do notapply to published IFR routes or procedures.

d. VOR/DME/TACAN Standard Service Vol-umes (SSV).

1. Standard service volumes (SSVs) are graphi-cally shown in FIG 1−1−1, FIG 1−1−2, FIG 1−1−3,FIG 1−1−4, and FIG 1−1−5. The SSV of a station isindicated by using the class designator as a prefix tothe station type designation.

EXAMPLE−TVOR, LDME, and HVORTAC.

FIG 1−1−1

Standard High Altitude Service Volume(See FIG 1−1−5 for altitudes below 1,000 feet).

60,000 ft.100 NM

130 NM

45,000 ft.

18,000 ft.

14,500 ft.

1,000 ft. 40 NM

FIG 1−1−2

Standard Low Altitude Service Volume(See FIG 1−1−5 for altitudes below 1,000 feet).

NOTE: All elevations shown are with respectto the station’s site elevation (AGL).Coverage is not available in a cone ofairspace directly above the facility.

40 NM

18,000 ft.

1,000 ft.

2. Within 25 NM, the bottom of the T servicevolume is defined by the curve in FIG 1−1−4. Within40 NM, the bottoms of the L and H service volumesare defined by the curve in FIG 1−1−5. (SeeTBL 1−1−1.)

e. Nondirectional Radio Beacon (NDB)

1. NDBs are classified according to theirintended use.

2. The ranges of NDB service volumes areshown in TBL 1−1−2. The distances (radius) are thesame at all altitudes.

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TBL 1−1−1

VOR/DME/TACAN Standard Service Volumes

SSV Class Designator Altitude and Range Boundaries

T (Terminal) . . . . . . . . From 1,000 feet above ground level (AGL) up to and including 12,000 feet AGL at radial distances outto 25 NM.

L (Low Altitude) . . . . From 1,000 feet AGL up to and including 18,000 feet AGL at radial distances out to 40 NM.

H (High Altitude) . . . . From 1,000 feet AGL up to and including 14,500 feet AGL at radial distances out to 40 NM. From14,500 AGL up to and including 60,000 feet at radial distances out to 100 NM. From 18,000 feet AGLup to and including 45,000 feet AGL at radial distances out to 130 NM.

TBL 1−1−2

NDB Service Volumes

Class Distance (Radius)

Compass Locator 15 NM

MH 25 NM

H 50 NM*

HH 75 NM

*Service ranges of individual facilities may be less than 50 nautical miles (NM). Restrictions to servicevolumes are first published as a Notice to Airmen and then with the alphabetical listing of the NAVAID inthe Chart Supplement U.S.

FIG 1−1−3

Standard Terminal Service Volume(See FIG 1−1−4 for altitudes below 1,000 feet).

25 NM

12,000 ft.

1,000 ft.

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FIG 1−1−4

Service Volume Lower Edge Terminal

1000

500

0

0 5 10 15 20 25

DISTANCE TO THE STATION IN NM

ALTIT

UDE

IN F

EET

FIG 1−1−5

Service Volume Lower EdgeStandard High and Low

1000

500

0

0 10 20 30 40

DISTANCE TO THE STATION IN NM

ALT

ITUD

E IN

FEE

T

5 15 25 35

1−1−9. Instrument Landing System (ILS)

a. General

1. The ILS is designed to provide an approachpath for exact alignment and descent of an aircraft onfinal approach to a runway.

2. The ground equipment consists of two highlydirectional transmitting systems and, along theapproach, three (or fewer) marker beacons. Thedirectional transmitters are known as the localizerand glide slope transmitters.

3. The system may be divided functionally intothree parts:

(a) Guidance information: localizer, glideslope;

(b) Range information: marker beacon,DME; and

(c) Visual information: approach lights,touchdown and centerline lights, runway lights.

4. Precision radar, or compass locators locatedat the Outer Marker (OM) or Middle Marker (MM),may be substituted for marker beacons. DME, when

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specified in the procedure, may be substituted for theOM.

5. Where a complete ILS system is installed oneach end of a runway; (i.e., the approach end ofRunway 4 and the approach end of Runway 22) theILS systems are not in service simultaneously.

b. Localizer

1. The localizer transmitter operates on one of40 ILS channels within the frequency range of108.10 to 111.95 MHz. Signals provide the pilot withcourse guidance to the runway centerline.

2. The approach course of the localizer is calledthe front course and is used with other functionalparts, e.g., glide slope, marker beacons, etc. Thelocalizer signal is transmitted at the far end of therunway. It is adjusted for a course width of (full scalefly−left to a full scale fly−right) of 700 feet at therunway threshold.

3. The course line along the extended centerlineof a runway, in the opposite direction to the frontcourse is called the back course.

CAUTION−Unless the aircraft’s ILS equipment includes reversesensing capability, when flying inbound on the backcourse it is necessary to steer the aircraft in the directionopposite the needle deflection when making correctionsfrom off−course to on−course. This “flying away from theneedle” is also required when flying outbound on thefront course of the localizer. Do not use back coursesignals for approach unless a back course approachprocedure is published for that particular runway and theapproach is authorized by ATC.

4. Identification is in International Morse Codeand consists of a three−letter identifier preceded bythe letter I ( � �) transmitted on the localizerfrequency.

EXAMPLE−I−DIA

5. The localizer provides course guidancethroughout the descent path to the runway thresholdfrom a distance of 18 NM from the antenna betweenan altitude of 1,000 feet above the highest terrainalong the course line and 4,500 feet above theelevation of the antenna site. Proper off−courseindications are provided throughout the followingangular areas of the operational service volume:

(a) To 10 degrees either side of the coursealong a radius of 18 NM from the antenna; and

(b) From 10 to 35 degrees either side of thecourse along a radius of 10 NM. (See FIG 1−1−6.)

FIG 1−1−6

Limits of Localizer Coverage

RUNWAYRUNWAY

LOCALIZERANTENNALOCALIZERANTENNA

10 N

M1

0 N

M

18 N

M1

8 N

M

NORMAL LIMITS OF LOCALIZERCOVERAGE: THE SAME AREAAPPLIES TO A BACK COURSEWHEN PROVIDED.

NORMAL LIMITS OF LOCALIZERCOVERAGE: THE SAME AREAAPPLIES TO A BACK COURSEWHEN PROVIDED.

10°

10°

35°

35°

6. Unreliable signals may be received outsidethese areas.

c. Localizer Type Directional Aid (LDA)

1. The LDA is of comparable use and accuracyto a localizer but is not part of a complete ILS. TheLDA course usually provides a more preciseapproach course than the similar SimplifiedDirectional Facility (SDF) installation, which mayhave a course width of 6 or 12 degrees.

2. The LDA is not aligned with the runway.Straight−in minimums may be published wherealignment does not exceed 30 degrees between thecourse and runway. Circling minimums only arepublished where this alignment exceeds 30 degrees.

3. A very limited number of LDA approachesalso incorporate a glideslope. These are annotated inthe plan view of the instrument approach chart witha note, “LDA/Glideslope.” These procedures fallunder a newly defined category of approaches calledApproach with Vertical Guidance (APV) described inparagraph 5−4−5, Instrument Approach ProcedureCharts, subparagraph a7(b), Approach with VerticalGuidance (APV). LDA minima for with and withoutglideslope is provided and annotated on the minimalines of the approach chart as S−LDA/GS andS−LDA. Because the final approach course is notaligned with the runway centerline, additionalmaneuvering will be required compared to an ILSapproach.

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d. Glide Slope/Glide Path

1. The UHF glide slope transmitter, operatingon one of the 40 ILS channels within the frequencyrange 329.15 MHz, to 335.00 MHz radiates its signalsin the direction of the localizer front course. The term“glide path” means that portion of the glide slope thatintersects the localizer.

CAUTION−False glide slope signals may exist in the area of thelocalizer back course approach which can cause the glideslope flag alarm to disappear and present unreliable glideslope information. Disregard all glide slope signalindications when making a localizer back courseapproach unless a glide slope is specified on the approachand landing chart.

2. The glide slope transmitter is located between750 feet and 1,250 feet from the approach end of therunway (down the runway) and offset 250 to 650 feetfrom the runway centerline. It transmits a glide pathbeam 1.4 degrees wide (vertically). The signalprovides descent information for navigation down tothe lowest authorized decision height (DH) specifiedin the approved ILS approach procedure. Theglidepath may not be suitable for navigation belowthe lowest authorized DH and any reference toglidepath indications below that height must besupplemented by visual reference to the runwayenvironment. Glidepaths with no published DH areusable to runway threshold.

3. The glide path projection angle is normallyadjusted to 3 degrees above horizontal so that itintersects the MM at about 200 feet and the OM atabout 1,400 feet above the runway elevation. Theglide slope is normally usable to the distance of10 NM. However, at some locations, the glide slopehas been certified for an extended service volumewhich exceeds 10 NM.

4. Pilots must be alert when approaching theglidepath interception. False courses and reversesensing will occur at angles considerably greater thanthe published path.

5. Make every effort to remain on the indicatedglide path.

CAUTION−Avoid flying below the glide path to assureobstacle/terrain clearance is maintained.

6. The published glide slope threshold crossingheight (TCH) DOES NOT represent the height of the

actual glide path on−course indication above therunway threshold. It is used as a reference forplanning purposes which represents the height abovethe runway threshold that an aircraft’s glide slopeantenna should be, if that aircraft remains on atrajectory formed by the four−mile−to−middlemarker glidepath segment.

7. Pilots must be aware of the vertical heightbetween the aircraft’s glide slope antenna and themain gear in the landing configuration and, at the DH,plan to adjust the descent angle accordingly if thepublished TCH indicates the wheel crossing heightover the runway threshold may not be satisfactory.Tests indicate a comfortable wheel crossing height isapproximately 20 to 30 feet, depending on the type ofaircraft.

NOTE−The TCH for a runway is established based on severalfactors including the largest aircraft category thatnormally uses the runway, how airport layout affects theglide slope antenna placement, and terrain. A higher thanoptimum TCH, with the same glide path angle, may causethe aircraft to touch down further from the threshold if thetrajectory of the approach is maintained until the flare.Pilots should consider the effect of a high TCH on therunway available for stopping the aircraft.

e. Distance Measuring Equipment (DME)

1. When installed with the ILS and specified inthe approach procedure, DME may be used:

(a) In lieu of the OM;

(b) As a back course (BC) final approach fix(FAF); and

(c) To establish other fixes on the localizercourse.

2. In some cases, DME from a separate facilitymay be used within Terminal Instrument Procedures(TERPS) limitations:

(a) To provide ARC initial approach seg-ments;

(b) As a FAF for BC approaches; and

(c) As a substitute for the OM.

f. Marker Beacon

1. ILS marker beacons have a rated poweroutput of 3 watts or less and an antenna arraydesigned to produce an elliptical pattern withdimensions, at 1,000 feet above the antenna, ofapproximately 2,400 feet in width and 4,200 feet in

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length. Airborne marker beacon receivers with aselective sensitivity feature should always beoperated in the “low” sensitivity position for properreception of ILS marker beacons.

2. Ordinarily, there are two marker beaconsassociated with an ILS, the OM and MM. Locationswith a Category II ILS also have an InnerMarker (IM). When an aircraft passes over a marker,the pilot will receive the indications shown inTBL 1−1−3.

(a) The OM normally indicates a position atwhich an aircraft at the appropriate altitude on thelocalizer course will intercept the ILS glide path.

(b) The MM indicates a position approxi-mately 3,500 feet from the landing threshold. This isalso the position where an aircraft on the glide pathwill be at an altitude of approximately 200 feet abovethe elevation of the touchdown zone.

(c) The IM will indicate a point at which anaircraft is at a designated decision height (DH) on theglide path between the MM and landing threshold.

TBL 1−1−3

Marker Passage Indications

Marker Code Light

OM � � � BLUE

MM � � � � AMBER

IM � � � � WHITE

BC � � � � WHITE

3. A back course marker normally indicates theILS back course final approach fix where approachdescent is commenced.

g. Compass Locator

1. Compass locator transmitters are oftensituated at the MM and OM sites. The transmittershave a power of less than 25 watts, a range of at least15 miles and operate between 190 and 535 kHz. Atsome locations, higher powered radio beacons, up to400 watts, are used as OM compass locators. Thesegenerally carry Transcribed Weather Broadcast(TWEB) information.

2. Compass locators transmit two letter identi-fication groups. The outer locator transmits the firsttwo letters of the localizer identification group, and

the middle locator transmits the last two letters of thelocalizer identification group.

h. ILS Frequency (See TBL 1−1−4.)

TBL 1−1−4

Frequency Pairs Allocated for ILS

Localizer MHz Glide Slope

108.10 334.70

108.15 334.55

108.3 334.10

108.35 333.95

108.5 329.90

108.55 329.75

108.7 330.50

108.75 330.35

108.9 329.30

108.95 329.15

109.1 331.40

109.15 331.25

109.3 332.00

109.35 331.85

109.50 332.60

109.55 332.45

109.70 333.20

109.75 333.05

109.90 333.80

109.95 333.65

110.1 334.40

110.15 334.25

110.3 335.00

110.35 334.85

110.5 329.60

110.55 329.45

Localizer MHz Glide Slope110.70 330.20

110.75 330.05

110.90 330.80

110.95 330.65

111.10 331.70

111.15 331.55

111.30 332.30

111.35 332.15

111.50 332.9

111.55 332.75

111.70 333.5

111.75 333.35

111.90 331.1

111.95 330.95

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i. ILS Minimums

1. The lowest authorized ILS minimums, withall required ground and airborne systems componentsoperative, are:

(a) Category I. Decision Height (DH)200 feet and Runway Visual Range (RVR) 2,400 feet(with touchdown zone and centerline lighting, RVR1,800 feet), or (with Autopilot or FD or HUD, RVR1,800 feet);

(b) Special Authorization Category I.DH 150 feet and Runway Visual Range (RVR) 1,400feet, HUD to DH;

(c) Category II. DH 100 feet and RVR 1,200feet (with autoland or HUD to touchdown and notedon authorization, RVR 1,000 feet);

(d) Special Authorization Category II withReduced Lighting. DH 100 feet and RVR 1,200 feetwith autoland or HUD to touchdown and noted onauthorization (touchdown zone, centerline lighting,and ALSF−2 are not required);

(e) Category IIIa. No DH or DH below 100feet and RVR not less than 700 feet;

(f) Category IIIb. No DH or DH below 50feet and RVR less than 700 feet but not less than 150feet; and

(g) Category IIIc. No DH and no RVRlimitation.

NOTE−Special authorization and equipment required forCategories II and III.

j. Inoperative ILS Components

1. Inoperative localizer. When the localizerfails, an ILS approach is not authorized.

2. Inoperative glide slope. When the glideslope fails, the ILS reverts to a non−precisionlocalizer approach.

REFERENCE−See the inoperative component table in the U.S. Government TerminalProcedures Publication (TPP), for adjustments to minimums due toinoperative airborne or ground system equipment.

k. ILS Course Distortion

1. All pilots should be aware that disturbances toILS localizer and glide slope courses may occur whensurface vehicles or aircraft are operated near thelocalizer or glide slope antennas. Most ILS

installations are subject to signal interference byeither surface vehicles, aircraft or both. ILSCRITICAL AREAS are established near eachlocalizer and glide slope antenna.

2. ATC issues control instructions to avoidinterfering operations within ILS critical areas atcontrolled airports during the hours the AirportTraffic Control Tower (ATCT) is in operation asfollows:

(a) Weather Conditions. Official weatherobservation is a ceiling of less than 800 feet and/orvisibility 2 miles.

(1) Localizer Critical Area. Except foraircraft that land, exit a runway, depart, or execute amissed approach, vehicles and aircraft are notauthorized in or over the critical area when an arrivingaircraft is inside the outer marker (OM) or the fixused in lieu of the OM. Additionally, whenever theofficial weather observation is a ceiling of less than200 feet or RVR less than 2,000 feet, do not authorizevehicles or aircraft operations in or over the areawhen an arriving aircraft is inside the MM, or in theabsence of a MM, ½ mile final.

(2) Glide Slope Critical Area. Do notauthorize vehicles or aircraft operations in or over thearea when an arriving aircraft is inside the ILS outermarker (OM), or the fix used in lieu of the OM, unlessthe arriving aircraft has reported the runway in sightand is circling or side−stepping to land on anotherrunway.

(b) Weather Conditions. At or above ceil-ing 800 feet and/or visibility 2 miles.

(1) No critical area protective action isprovided under these conditions.

(2) A flight crew, under these conditions,should advise the tower that it will conduct anAUTOLAND or COUPLED approach.

EXAMPLE−Denver Tower, United 1153, Request Autoland/CoupledApproach (runway)ATC replies with:United 1153, Denver Tower, Roger, Critical Areas notprotected.

3. Aircraft holding below 5,000 feet betweenthe outer marker and the airport may cause localizersignal variations for aircraft conducting the ILSapproach. Accordingly, such holding is not autho-

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rized when weather or visibility conditions are lessthan ceiling 800 feet and/or visibility 2 miles.

4. Pilots are cautioned that vehicular traffic notsubject to ATC may cause momentary deviation toILS course or glide slope signals. Also, critical areasare not protected at uncontrolled airports or at airportswith an operating control tower when weather orvisibility conditions are above those requiringprotective measures. Aircraft conducting coupled orautoland operations should be especially alert inmonitoring automatic flight control systems. (See FIG 1−1−7.)

NOTE−Unless otherwise coordinated through Flight Standards,ILS signals to Category I runways are not flight inspectedbelow the point that is 100 feet less than the decisionaltitude (DA). Guidance signal anomalies may beencountered below this altitude.

1−1−10. Simplified Directional Facility(SDF)

a. The SDF provides a final approach coursesimilar to that of the ILS localizer. It does not provideglide slope information. A clear understanding of theILS localizer and the additional factors listed belowcompletely describe the operational characteristicsand use of the SDF.

b. The SDF transmits signals within the range of108.10 to 111.95 MHz.

c. The approach techniques and procedures usedin an SDF instrument approach are essentially thesame as those employed in executing a standardlocalizer approach except the SDF course may not bealigned with the runway and the course may be wider,resulting in less precision.

d. Usable off−course indications are limited to35 degrees either side of the course centerline.Instrument indications received beyond 35 degreesshould be disregarded.

e. The SDF antenna may be offset from the runwaycenterline. Because of this, the angle of convergencebetween the final approach course and the runwaybearing should be determined by reference to theinstrument approach procedure chart. This angle isgenerally not more than 3 degrees. However, it shouldbe noted that inasmuch as the approach courseoriginates at the antenna site, an approach which iscontinued beyond the runway threshold will lead theaircraft to the SDF offset position rather than alongthe runway centerline.

f. The SDF signal is fixed at either 6 degrees or12 degrees as necessary to provide maximumflyability and optimum course quality.

g. Identification consists of a three−letter identifi-er transmitted in Morse Code on the SDF frequency.The appropriate instrument approach chart willindicate the identifier used at a particular airport.

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FIG 1−1−7

FAA Instrument Landing Systems

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1−1−11. NAVAID Identifier Removal DuringMaintenance

During periods of routine or emergency maintenance,coded identification (or code and voice, whereapplicable) is removed from certain FAA NAVAIDs.Removal of identification serves as a warning topilots that the facility is officially off the air fortune−up or repair and may be unreliable even thoughintermittent or constant signals are received.

NOTE−During periods of maintenance VHF ranges may radiatea T−E−S−T code (- � �� -).

NOTE−DO NOT attempt to fly a procedure that is NOTAMed outof service even if the identification is present. In certaincases, the identification may be transmitted for shortperiods as part of the testing.

1−1−12. NAVAIDs with Voice

a. Voice equipped en route radio navigational aidsare under the operational control of either a FlightService Station (FSS) or an approach control facility.The voice communication is available on somefacilities. Hazardous Inflight Weather AdvisoryService (HIWAS) broadcast capability is available onselected VOR sites throughout the conterminous U.S.and does not provide two-way voice communication.The availability of two-way voice communicationand HIWAS is indicated in the Chart SupplementU.S. and aeronautical charts.

b. Unless otherwise noted on the chart, all radionavigation aids operate continuously except duringshutdowns for maintenance. Hours of operation offacilities not operating continuously are annotated oncharts and in the Chart Supplement U.S.

1−1−13. User Reports Requested onNAVAID or Global Navigation SatelliteSystem (GNSS) Performance orInterference

a. Users of the National Airspace System (NAS)can render valuable assistance in the early correctionof NAVAID malfunctions or GNSS problems and areencouraged to report their observations of undesir-able avionics performance. Although NAVAIDs aremonitored by electronic detectors, adverse effects ofelectronic interference, new obstructions, or changesin terrain near the NAVAID can exist without

detection by the ground monitors. Some of thecharacteristics of malfunction or deterioratingperformance which should be reported are: erraticcourse or bearing indications; intermittent, or full,flag alarm; garbled, missing or obviously impropercoded identification; poor quality communicationsreception; or, in the case of frequency interference, anaudible hum or tone accompanying radio communi-cations or NAVAID identification. GNSS problemsare often characterized by navigation degradation orservice loss indications. For instance, pilots conduct-ing operations in areas where there is GNSSinterference may be unable to use GPS for navigation,and ADS−B may be unavailable for surveillance.Radio frequency interference may affect bothnavigation for the pilot and surveillance by the airtraffic controller. Depending on the equipment andintegration, either an advisory light or message mayalert the pilot. Air traffic controllers monitoringADS−B reports may stop receiving ADS−B positionmessages and associated aircraft tracks.

In addition, malfunctioning, faulty, inappropriatelyinstalled, operated, or modified GPS re−radiatorsystems, intended to be used for aircraft maintenanceactivities, have resulted in unintentional disruptionof aviation GNSS receivers. This type of disruptioncould result in un−flagged, erroneous positioninformation output to primary flight displays/indica-tors and to other aircraft and air traffic controlsystems. Since receiver autonomous integritymonitoring (RAIM) is only partially effective againstthis type of disruption (effectively a “signalspoofing”), the pilot may not be aware of anyerroneous navigation indications; ATC may be theonly means available for identification of thesedisruptions and detect unexpected aircraft positionwhile monitoring aircraft for IFR separation.

b. Pilots reporting potential interference shouldidentify the NAVAID (for example, VOR) malfunc-tion or GNSS problem, location of the aircraft (that is,latitude, longitude or bearing/distance from areference NAVAID), magnetic heading, altitude, dateand time of the observation, type of aircraft(make/model/call sign), and description of thecondition observed, and the type of receivers in use(that is, make/model/software revision). Reportsshould be made in any of the following ways:

1. Immediately, by voice radio communicationto the controlling ATC facility or FSS.

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2. By telephone to the nearest ATC facilitycontrolling the airspace where the disruption wasexperienced.

3. Additionally, GNSS problems should bereported by Internet via the GPS Anomaly ReportingForm at http://www.faa.gov/air_traffic/nas/gps_reports/.

c. In aircraft equipped with more than one avionicsreceiver, there are many combinations of potentialinterference between units that could causeerroneous navigation indications, or complete orpartial blanking out of the display.

NOTE−GPS interference or outages associated with knowntesting NOTAMs should not be reported to ATC.

1−1−14. LORAN

NOTE−In accordance with the 2010 DHS Appropriations Act, theU.S. Coast Guard (USCG) terminated the transmission ofall U.S. LORAN−C signals on 08 Feb 2010. The USCG alsoterminated the transmission of the Russian Americansignals on 01 Aug 2010, and the Canadian LORAN−Csignals on 03 Aug 2010. For more information, visithttp://www.navcen.uscg.gov. Operators should also notethat TSO−C60b, AIRBORNE AREA NAVIGATIONEQUIPMENT USING LORAN−C INPUTS, has beencanceled by the FAA.

1−1−15. Inertial Reference Unit (IRU),Inertial Navigation System (INS), andAttitude Heading Reference System (AHRS)

a. IRUs are self−contained systems comprised ofgyros and accelerometers that provide aircraftattitude (pitch, roll, and heading), position, andvelocity information in response to signals resultingfrom inertial effects on system components. Oncealigned with a known position, IRUs continuouslycalculate position and velocity. IRU positionaccuracy decays with time. This degradation isknown as “drift.”

b. INSs combine the components of an IRU withan internal navigation computer. By programming aseries of waypoints, these systems will navigate alonga predetermined track.

c. AHRSs are electronic devices that provideattitude information to aircraft systems such as

weather radar and autopilot, but do not directlycompute position information.

d. Aircraft equipped with slaved compass systemsmay be susceptible to heading errors caused byexposure to magnetic field disturbances (flux fields)found in materials that are commonly located on thesurface or buried under taxiways and ramps. Thesematerials generate a magnetic flux field that can besensed by the aircraft’s compass system flux detectoror “gate”, which can cause the aircraft’s system toalign with the material’s magnetic field rather thanthe earth’s natural magnetic field. The system’serroneous heading may not self-correct. Prior to takeoff pilots should be aware that a headingmisalignment may have occurred during taxi. Pilotsare encouraged to follow the manufacturer’s or otherappropriate procedures to correct possible headingmisalignment before take off is commenced.

1−1−16. Doppler Radar

Doppler Radar is a semiautomatic self−containeddead reckoning navigation system (radar sensor pluscomputer) which is not continuously dependent oninformation derived from ground based or externalaids. The system employs radar signals to detect andmeasure ground speed and drift angle, using theaircraft compass system as its directional reference.Doppler is less accurate than INS, however, and theuse of an external reference is required for periodicupdates if acceptable position accuracy is to beachieved on long range flights.

1−1−17. Global Positioning System (GPS)

a. System Overview

1. System Description. The Global PositioningSystem is a space-based radio navigation systemused to determine precise position anywhere in theworld. The 24 satellite constellation is designed toensure at least five satellites are always visible to auser worldwide. A minimum of four satellites isnecessary for receivers to establish an accuratethree−dimensional position. The receiver uses datafrom satellites above the mask angle (the lowestangle above the horizon at which a receiver can usea satellite). The Department of Defense (DOD) isresponsible for operating the GPS satellite constella-tion and monitors the GPS satellites to ensure properoperation. Each satellite’s orbital parameters (eph-emeris data) are sent to each satellite for broadcast as

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part of the data message embedded in the GPS signal.The GPS coordinate system is the Cartesianearth−centered, earth−fixed coordinates as specifiedin the World Geodetic System 1984 (WGS−84).

2. System Availability and Reliability.

(a) The status of GPS satellites is broadcast aspart of the data message transmitted by the GPSsatellites. GPS status information is also available bymeans of the U.S. Coast Guard navigationinformation service: (703) 313−5907, Internet:http://www.navcen.uscg.gov/. Additionally, satel-lite status is available through the Notice to Airmen(NOTAM) system.

(b) GNSS operational status depends on thetype of equipment being used. For GPS−onlyequipment TSO−C129 or TSO-C196(), the opera-tional status of non−precision approach capability forflight planning purposes is provided through aprediction program that is embedded in the receiveror provided separately.

3. Receiver Autonomous Integrity Monitoring(RAIM). RAIM is the capability of a GPS receiver toperform integrity monitoring on itself by ensuringavailable satellite signals meet the integrity require-ments for a given phase of flight. Without RAIM, thepilot has no assurance of the GPS position integrity.RAIM provides immediate feedback to the pilot. Thisfault detection is critical for performance-basednavigation (PBN)(see Paragraph 1−2−1, Perform-ance−Based Navigation (PBN) and Area Navigation(RNAV), for an introduction to PBN), because delaysof up to two hours can occur before an erroneoussatellite transmission is detected and corrected by thesatellite control segment.

(a) In order for RAIM to determine if asatellite is providing corrupted information, at leastone satellite, in addition to those required fornavigation, must be in view for the receiver toperform the RAIM function. RAIM requires aminimum of 5 satellites, or 4 satellites and barometricaltimeter input (baro−aiding), to detect an integrityanomaly. Baro−aiding is a method of augmenting theGPS integrity solution by using a non-satellite inputsource in lieu of the fifth satellite. Some GPSreceivers also have a RAIM capability, called faultdetection and exclusion (FDE), that excludes a failedsatellite from the position solution; GPS receiverscapable of FDE require 6 satellites or 5 satellites with

baro−aiding. This allows the GPS receiver to isolatethe corrupt satellite signal, remove it from theposition solution, and still provide an integrity-as-sured position. To ensure that baro−aiding isavailable, enter the current altimeter setting into thereceiver as described in the operating manual. Do notuse the GPS derived altitude due to the large GPSvertical errors that will make the integrity monitoringfunction invalid.

(b) There are generally two types of RAIMfault messages. The first type of message indicatesthat there are not enough satellites available toprovide RAIM integrity monitoring. The GPSnavigation solution may be acceptable, but theintegrity of the solution cannot be determined. Thesecond type indicates that the RAIM integritymonitor has detected a potential error and that thereis an inconsistency in the navigation solution for thegiven phase of flight. Without RAIM capability, thepilot has no assurance of the accuracy of the GPSposition.

4. Selective Availability. Selective Availability(SA) is a method by which the accuracy of GPS isintentionally degraded. This feature was designed todeny hostile use of precise GPS positioning data. SAwas discontinued on May 1, 2000, but many GPSreceivers are designed to assume that SA is stillactive. New receivers may take advantage of thediscontinuance of SA based on the performancevalues in ICAO Annex 10.

b. Operational Use of GPS. U.S. civil operatorsmay use approved GPS equipment in oceanicairspace, certain remote areas, the National AirspaceSystem and other States as authorized (please consultthe applicable Aeronautical Information Publica-tion). Equipage other than GPS may be required forthe desired operation. GPS navigation is used for bothVisual Flight Rules (VFR) and Instrument FlightRules (IFR) operations.

1. VFR Operations

(a) GPS navigation has become an asset toVFR pilots by providing increased navigationalcapabilities and enhanced situational awareness.Although GPS has provided many benefits to theVFR pilot, care must be exercised to ensure thatsystem capabilities are not exceeded. VFR pilotsshould integrate GPS navigation with electronicnavigation (when possible), as well as pilotage anddead reckoning.

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(b) GPS receivers used for VFR navigationvary from fully integrated IFR/VFR installation usedto support VFR operations to hand−held devices.Pilots must understand the limitations of the receiversprior to using in flight to avoid misusing navigationinformation. (See TBL 1−1−6.) Most receivers arenot intuitive. The pilot must learn the variouskeystrokes, knob functions, and displays that areused in the operation of the receiver. Somemanufacturers provide computer−based tutorials orsimulations of their receivers that pilots can use tobecome familiar with operating the equipment.

(c) When using GPS for VFR operations,RAIM capability, database currency, and antennalocation are critical areas of concern.

(1) RAIM Capability. VFR GPS panelmount receivers and hand−held units have no RAIMalerting capability. This prevents the pilot from beingalerted to the loss of the required number of satellitesin view, or the detection of a position error. Pilotsshould use a systematic cross−check with othernavigation techniques to verify position. Besuspicious of the GPS position if a disagreementexists between the two positions.

(2) Database Currency. Check the curren-cy of the database. Databases must be updated forIFR operations and should be updated for all otheroperations. However, there is no requirement fordatabases to be updated for VFR navigation. It is notrecommended to use a moving map with an outdateddatabase in and around critical airspace. Pilots usingan outdated database should verify waypoints usingcurrent aeronautical products; for example, ChartSupplement U.S., Sectional Chart, or En RouteChart.

(3) Antenna Location. The antenna loca-tion for GPS receivers used for IFR and VFRoperations may differ. VFR antennae are typicallyplaced for convenience more than performance,while IFR installations ensure a clear view isprovided with the satellites. Antennae not providinga clear view have a greater opportunity to lose thesatellite navigational signal. This is especially truein the case of hand−held GPS receivers. Typically,suction cups are used to place the GPS antennas onthe inside of cockpit windows. While this method hasgreat utility, the antenna location is limited to thecockpit or cabin which rarely provides a clear viewof all available satellites. Consequently, signal losses

may occur due to aircraft structure blocking satellitesignals, causing a loss of navigation capability. Theselosses, coupled with a lack of RAIM capability, couldpresent erroneous position and navigation informa-tion with no warning to the pilot. While the use of ahand−held GPS for VFR operations is not limited byregulation, modification of the aircraft, such asinstalling a panel− or yoke−mounted holder, isgoverned by 14 CFR Part 43. Consult with yourmechanic to ensure compliance with the regulationand safe installation.

(d) Do not solely rely on GPS for VFRnavigation. No design standard of accuracy orintegrity is used for a VFR GPS receiver. VFR GPSreceivers should be used in conjunction with otherforms of navigation during VFR operations to ensurea correct route of flight is maintained. Minimizehead−down time in the aircraft by being familiar withyour GPS receiver’s operation and by keeping eyesoutside scanning for traffic, terrain, and obstacles.

(e) VFR Waypoints

(1) VFR waypoints provide VFR pilotswith a supplementary tool to assist with positionawareness while navigating visually in aircraftequipped with area navigation receivers. VFRwaypoints should be used as a tool to supplementcurrent navigation procedures. The uses of VFRwaypoints include providing navigational aids forpilots unfamiliar with an area, waypoint definition ofexisting reporting points, enhanced navigation in andaround Class B and Class C airspace, and enhancednavigation around Special Use Airspace. VFR pilotsshould rely on appropriate and current aeronauticalcharts published specifically for visual navigation. Ifoperating in a terminal area, pilots should takeadvantage of the Terminal Area Chart available forthat area, if published. The use of VFR waypointsdoes not relieve the pilot of any responsibility tocomply with the operational requirements of 14 CFRPart 91.

(2) VFR waypoint names (for computer−entry and flight plans) consist of five lettersbeginning with the letters “VP” and are retrievablefrom navigation databases. The VFR waypointnames are not intended to be pronounceable, and theyare not for use in ATC communications. On VFRcharts, stand−alone VFR waypoints will be portrayedusing the same four−point star symbol used for IFRwaypoints. VFR waypoints collocated with visualcheck points on the chart will be identified by small

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magenta flag symbols. VFR waypoints collocatedwith visual check points will be pronounceable basedon the name of the visual check point and may be usedfor ATC communications. Each VFR waypoint namewill appear in parentheses adjacent to the geographiclocation on the chart. Latitude/longitude data for allestablished VFR waypoints may be found in theappropriate regional Chart Supplement U.S.

(3) VFR waypoints may not be used on IFRflight plans. VFR waypoints are not recognized by theIFR system and will be rejected for IFR routingpurposes.

(4) Pilots may use the five−letter identifieras a waypoint in the route of flight section on a VFRflight plan. Pilots may use the VFR waypoints onlywhen operating under VFR conditions. The pointmay represent an intended course change or describethe planned route of flight. This VFR filing would besimilar to how a VOR would be used in a route offlight.

(5) VFR waypoints intended for use duringflight should be loaded into the receiver while on theground. Once airborne, pilots should avoid program-ming routes or VFR waypoint chains into theirreceivers.

(6) Pilots should be vigilant to see andavoid other traffic when near VFR waypoints. Withthe increased use of GPS navigation and accuracy,expect increased traffic near VFR waypoints.Regardless of the class of airspace, monitor theavailable ATC frequency for traffic information onother aircraft operating in the vicinity. See Paragraph7−5−2, VFR in Congested Areas, for moreinformation.

2. IFR Use of GPS

(a) General Requirements. Authorizationto conduct any GPS operation under IFR requires:

(1) GPS navigation equipment used for IFRoperations must be approved in accordance with therequirements specified in Technical Standard Order(TSO) TSO−C129(), TSO−C196(), TSO−C145(), orTSO−C146(), and the installation must be done inaccordance with Advisory Circular AC 20−138,Airworthiness Approval of Positioning and Naviga-tion Systems. Equipment approved in accordancewith TSO−C115a does not meet the requirements ofTSO−C129. Visual flight rules (VFR) and hand−held

GPS systems are not authorized for IFR navigation,instrument approaches, or as a principal instrumentflight reference.

(2) Aircraft using un-augmented GPS(TSO-C129() or TSO-C196()) for navigation underIFR must be equipped with an alternate approved andoperational means of navigation suitable fornavigating the proposed route of flight. (Examples ofalternate navigation equipment include VOR orDME/DME/IRU capability). Active monitoring ofalternative navigation equipment is not requiredwhen RAIM is available for integrity monitoring.Active monitoring of an alternate means ofnavigation is required when the GPS RAIMcapability is lost.

(3) Procedures must be established for usein the event that the loss of RAIM capability ispredicted to occur. In situations where RAIM ispredicted to be unavailable, the flight must rely onother approved navigation equipment, re-route towhere RAIM is available, delay departure, or cancelthe flight.

(4) The GPS operation must be conductedin accordance with the FAA−approved aircraft flightmanual (AFM) or flight manual supplement. Flightcrew members must be thoroughly familiar with theparticular GPS equipment installed in the aircraft, thereceiver operation manual, and the AFM or flightmanual supplement. Operation, receiver presenta-tion and capabilities of GPS equipment vary. Due tothese differences, operation of GPS receivers ofdifferent brands, or even models of the same brand,under IFR should not be attempted without thoroughoperational knowledge. Most receivers have abuilt−in simulator mode, which allows the pilot tobecome familiar with operation prior to attemptingoperation in the aircraft.

(5) Aircraft navigating by IFR−approvedGPS are considered to be performance−basednavigation (PBN) aircraft and have special equip-ment suffixes. File the appropriate equipment suffixin accordance with TBL 5−1−3 on the ATC flightplan. If GPS avionics become inoperative, the pilotshould advise ATC and amend the equipment suffix.

(6) Prior to any GPS IFR operation, thepilot must review appropriate NOTAMs andaeronautical information. (See GPS NOTAMs/Aero-nautical Information).

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(b) Database Requirements. The onboardnavigation data must be current and appropriate forthe region of intended operation and should includethe navigation aids, waypoints, and relevant codedterminal airspace procedures for the departure,arrival, and alternate airfields.

(1) Further database guidance for terminaland en route requirements may be found in AC90-100, U.S. Terminal and En Route AreaNavigation (RNAV) Operations.

(2) Further database guidance on RequiredNavigation Performance (RNP) instrument approachoperations, RNP terminal, and RNP en routerequirements may be found in AC 90-105, ApprovalGuidance for RNP Operations and BarometricVertical Navigation in the U.S. National AirspaceSystem.

(3) All approach procedures to be flownmust be retrievable from the current airbornenavigation database supplied by the equipmentmanufacturer or other FAA−approved source. Thesystem must be able to retrieve the procedure by namefrom the aircraft navigation database, not just as amanually entered series of waypoints. Manual entryof waypoints using latitude/longitude or place/bear-ing is not permitted for approach procedures.

(4) Prior to using a procedure or waypointretrieved from the airborne navigation database, thepilot should verify the validity of the database. Thisverification should include the following preflightand inflight steps:

[a] Preflight:

[1] Determine the date of databaseissuance, and verify that the date/time of proposeduse is before the expiration date/time.

[2] Verify that the database providerhas not published a notice limiting the use of thespecific waypoint or procedure.

[b] Inflight:

[1] Determine that the waypointsand transition names coincide with names found onthe procedure chart. Do not use waypoints which donot exactly match the spelling shown on publishedprocedure charts.

[2] Determine that the waypoints arelogical in location, in the correct order, and their

orientation to each other is as found on the procedurechart, both laterally and vertically.

NOTE−There is no specific requirement to check each waypointlatitude and longitude, type of waypoint and/or altitudeconstraint, only the general relationship of waypoints inthe procedure, or the logic of an individual waypoint’slocation.

[3] If the cursory check of procedurelogic or individual waypoint location, specified in [b]above, indicates a potential error, do not use theretrieved procedure or waypoint until a verification oflatitude and longitude, waypoint type, and altitudeconstraints indicate full conformity with thepublished data.

(5) Air carrier and commercial operatorsmust meet the appropriate provisions of theirapproved operations specifications.

[a] During domestic operations for com-merce or for hire, operators must have a secondnavigation system capable of reversion or contin-gency operations.

[b] Operators must have two independ-ent navigation systems appropriate to the route to beflown, or one system that is suitable and a second,independent backup capability that allows theoperator to proceed safely and land at a differentairport, and the aircraft must have sufficient fuel(reference 14 CFR 121.349, 125.203, 129.17, and135.165). These rules ensure the safety of theoperation by preventing a single point of failure.

NOTE−An aircraft approved for multi-sensor navigation andequipped with a single navigation system must maintain anability to navigate or proceed safely in the event that anyone component of the navigation system fails, including theflight management system (FMS). Retaining a FMS-inde-pendent VOR capability would satisfy this requirement.

[c] The requirements for a secondsystem apply to the entire set of equipment needed toachieve the navigation capability, not just theindividual components of the system such as the radionavigation receiver. For example, to use two RNAVsystems (e.g., GPS and DME/DME/IRU) to complywith the requirements, the aircraft must be equippedwith two independent radio navigation receivers andtwo independent navigation computers (e.g., flightmanagement systems (FMS)). Alternatively, tocomply with the requirements using a single RNAVsystem with an installed and operable VOR

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capability, the VOR capability must be independentof the FMS.

[d] To satisfy the requirement for twoindependent navigation systems, if the primarynavigation system is GPS−based, the second systemmust be independent of GPS (for example, VOR orDME/DME/IRU). This allows continued navigationin case of failure of the GPS or WAAS services.Recognizing that GPS interference and test eventsresulting in the loss of GPS services have becomemore common, the FAA requires operators conduct-ing IFR operations under 14 CFR 121.349, 125.203,129.17 and 135.65 to retain a non-GPS navigationcapability consisting of either DME/DME, IRU, orVOR for en route and terminal operations, and VORand ILS for final approach. Since this system is to beused as a reversionary capability, single equipage issufficient.

3. Oceanic, Domestic , En Route, andTerminal Area Operations

(a) Conduct GPS IFR operations in oceanicareas only when approved avionics systems areinstalled. TSO−C196() users and TSO−C129() GPSusers authorized for Class A1, A2, B1, B2, C1, or C2operations may use GPS in place of another approvedmeans of long−range navigation, such as dual INS.(See TBL 1−1−5 and TBL 1−1−6.) Aircraft with asingle installation GPS, meeting the above specifica-tions, are authorized to operate on short oceanicroutes requiring one means of long−range navigation(reference AC 20-138, Appendix 1).

(b) Conduct GPS domestic, en route, andterminal IFR operations only when approvedavionics systems are installed. Pilots may use GPSvia TSO−C129() authorized for Class A1, B1, B3,C1, or C3 operations GPS via TSO-C196(); orGPS/WAAS with either TSO-C145() orTSO-C146(). When using TSO-C129() orTSO-C196() receivers, the avionics necessary toreceive all of the ground−based facilities appropriatefor the route to the destination airport and anyrequired alternate airport must be installed andoperational. Ground−based facilities necessary forthese routes must be operational.

(1) GPS en route IFR operations may beconducted in Alaska outside the operational servicevolume of ground−based navigation aids when aTSO−C145() or TSO−C146() GPS/wide area aug-

mentation system (WAAS) system is installed andoperating. WAAS is the U.S. version of asatellite-based augmentation system (SBAS).

[a] In Alaska, aircraft may operate onGNSS Q-routes with GPS (TSO-C129 () orTSO-C196 ()) equipment while the aircraft remainsin Air Traffic Control (ATC) radar surveillance orwith GPS/WAAS (TSO-C145 () or TSO-C146 ())which does not require ATC radar surveillance.

[b] In Alaska, aircraft may only operateon GNSS T-routes with GPS/WAAS (TSO-C145 () orTSO-C146 ()) equipment.

(2) Ground−based navigation equipmentis not required to be installed and operating for enroute IFR operations when using GPS/WAASnavigation systems. All operators should ensure thatan alternate means of navigation is available in theunlikely event the GPS/WAAS navigation systembecomes inoperative.

(3) Q-routes and T-routes outside Alaska.Q-routes require system performance currently metby GPS, GPS/WAAS, or DME/DME/IRU RNAVsystems that satisfy the criteria discussed in AC90−100, U.S. Terminal and En Route AreaNavigation (RNAV) Operations. T-routes requireGPS or GPS/WAAS equipment.

REFERENCE−AIM, Paragraph 5−3−4 , Airways and Route Systems

(c) GPS IFR approach/departure operationscan be conducted when approved avionics systemsare installed and the following requirements are met:

(1) The aircraft is TSO−C145() or TSO−C146() or TSO−C196() or TSO−C129() in Class A1,B1, B3, C1, or C3; and

(2) The approach/departure must be re-trievable from the current airborne navigationdatabase in the navigation computer. The systemmust be able to retrieve the procedure by name fromthe aircraft navigation database. Manual entry ofwaypoints using latitude/longitude or place/bearingis not permitted for approach procedures.

(3) The authorization to fly instrumentapproaches/departures with GPS is limited to U.S.airspace.

(4) The use of GPS in any other airspacemust be expressly authorized by the FAA Adminis-trator.

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(5) GPS instrument approach/departureoperations outside the U.S. must be authorized bythe appropriate sovereign authority.

4. Departures and Instrument DepartureProcedures (DPs)

The GPS receiver must be set to terminal (±1 NM)CDI sensitivity and the navigation routes contained inthe database in order to fly published IFR charteddepartures and DPs. Terminal RAIM should beautomatically provided by the receiver. (TerminalRAIM for departure may not be available unless thewaypoints are part of the active flight plan rather thanproceeding direct to the first destination.) Certainsegments of a DP may require some manualintervention by the pilot, especially when radarvectored to a course or required to intercept a specificcourse to a waypoint. The database may not containall of the transitions or departures from all runwaysand some GPS receivers do not contain DPs in thedatabase. It is necessary that helicopter procedures beflown at 70 knots or less since helicopter departureprocedures and missed approaches use a 20:1obstacle clearance surface (OCS), which is doublethe fixed−wing OCS, and turning areas are based onthis speed as well.

5. GPS Instrument Approach Procedures

(a) GPS overlay approaches are designatednon−precision instrument approach procedures thatpilots are authorized to fly using GPS avionics.Localizer (LOC), localizer type directional aid(LDA), and simplified directional facility (SDF)procedures are not authorized. Overlay proceduresare identified by the “name of the procedure” and “orGPS” (e.g., VOR/DME or GPS RWY 15) in the title.Authorized procedures must be retrievable from acurrent onboard navigation database. The naviga-tion database may also enhance position orientationby displaying a map containing information onconventional NAVAID approaches. This approachinformation should not be confused with a GPSoverlay approach (see the receiver operatingmanual, AFM, or AFM Supplement for details onhow to identify these approaches in the navigationdatabase).

NOTE−Overlay approaches do not adhere to the design criteriadescribed in Paragraph 5−4−5m, Area Navigation (RNAV)Instrument Approach Charts, for stand−alone GPS

approaches. Overlay approach criteria is based on thedesign criteria used for ground−based NAVAID ap-proaches.

(b) Stand−alone approach procedures spe-cifically designed for GPS systems have replacedmany of the original overlay approaches. Allapproaches that contain “GPS” in the title (e.g.,“VOR or GPS RWY 24,” “GPS RWY 24,” or“RNAV (GPS) RWY 24”) can be flown using GPS.GPS−equipped aircraft do not need underlyingground−based NAVAIDs or associated aircraftavionics to fly the approach. Monitoring theunderlying approach with ground−based NAVAIDs issuggested when able. Existing overlay approachesmay be requested using the GPS title; for example,the VOR or GPS RWY 24 may be requested as “GPSRWY 24.” Some GPS procedures have a TerminalArrival Area (TAA) with an underlining RNAVapproach.

(c) For flight planning purposes,TSO-C129() and TSO-C196()−equipped users(GPS users) whose navigation systems have faultdetection and exclusion (FDE) capability, whoperform a preflight RAIM prediction for theapproach integrity at the airport where the RNAV(GPS) approach will be flown, and have properknowledge and any required training and/orapproval to conduct a GPS-based IAP, may filebased on a GPS−based IAP at either the destinationor the alternate airport, but not at both locations. Atthe alternate airport, pilots may plan for:

(1) Lateral navigation (LNAV) or circlingminimum descent altitude (MDA);

(2) LNAV/vertical navigation (LNAV/VNAV) DA, if equipped with and using approvedbarometric vertical navigation (baro-VNAV) equip-ment;

(3) RNP 0.3 DA on an RNAV (RNP) IAP,if they are specifically authorized users usingapproved baro-VNAV equipment and the pilot hasverified required navigation performance (RNP)availability through an approved prediction program.

(d) If the above conditions cannot be met, anyrequired alternate airport must have an approvedinstrument approach procedure other than GPS−based that is anticipated to be operational andavailable at the estimated time of arrival, and whichthe aircraft is equipped to fly.

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(e) Procedures for Accomplishing GPSApproaches

(1) An RNAV (GPS) procedure may beassociated with a Terminal Arrival Area (TAA). Thebasic design of the RNAV procedure is the “T” designor a modification of the “T” (See Paragraph 5-4-5d,Terminal Arrival Area (TAA), for complete informa-tion).

(2) Pilots cleared by ATC for an RNAV(GPS) approach should fly the full approach from anInitial Approach Waypoint (IAWP) or feeder fix.Randomly joining an approach at an intermediate fixdoes not assure terrain clearance.

(3) When an approach has been loaded inthe navigation system, GPS receivers will give an“arm” annunciation 30 NM straight line distancefrom the airport/heliport reference point. Pilotsshould arm the approach mode at this time if notalready armed (some receivers arm automatically).Without arming, the receiver will not change fromen route CDI and RAIM sensitivity of ±5 NM eitherside of centerline to ±1 NM terminal sensitivity.Where the IAWP is inside this 30 mile point, a CDIsensitivity change will occur once the approach modeis armed and the aircraft is inside 30 NM. Where theIAWP is beyond 30 NM from the airport/heliportreference point and the approach is armed, the CDIsensitivity will not change until the aircraft is within30 miles of the airport/heliport reference point.Feeder route obstacle clearance is predicated on thereceiver being in terminal (±1 NM) CDI sensitivityand RAIM within 30 NM of the airport/heliportreference point; therefore, the receiver should alwaysbe armed (if required) not later than the 30 NMannunciation.

(4) The pilot must be aware of what bankangle/turn rate the particular receiver uses to computeturn anticipation, and whether wind and airspeed areincluded in the receiver’s calculations. This informa-tion should be in the receiver operating manual. Overor under banking the turn onto the final approachcourse may significantly delay getting on course andmay result in high descent rates to achieve the nextsegment altitude.

(5) When within 2 NM of the FinalApproach Waypoint (FAWP) with the approachmode armed, the approach mode will switch toactive, which results in RAIM and CDI changing to

approach sensitivity. Beginning 2 NM prior to theFAWP, the full scale CDI sensitivity will smoothlychange from ±1 NM to ±0.3 NM at the FAWP. Assensitivity changes from ±1 NM to ±0.3 NMapproaching the FAWP, with the CDI not centered,the corresponding increase in CDI displacementmay give the impression that the aircraft is movingfurther away from the intended course even though itis on an acceptable intercept heading. Referencing thedigital track displacement information (cross trackerror), if it is available in the approach mode, mayhelp the pilot remain position oriented in thissituation. Being established on the final approachcourse prior to the beginning of the sensitivity changeat 2 NM will help prevent problems in interpreting theCDI display during ramp down. Therefore, request-ing or accepting vectors which will cause the aircraftto intercept the final approach course within 2 NM ofthe FAWP is not recommended.

(6) When receiving vectors to final, mostreceiver operating manuals suggest placing thereceiver in the non−sequencing mode on the FAWPand manually setting the course. This provides anextended final approach course in cases where theaircraft is vectored onto the final approach courseoutside of any existing segment which is aligned withthe runway. Assigned altitudes must be maintaineduntil established on a published segment of theapproach. Required altitudes at waypoints outside theFAWP or stepdown fixes must be considered.Calculating the distance to the FAWP may berequired in order to descend at the proper location.

(7) Overriding an automatically selectedsensitivity during an approach will cancel theapproach mode annunciation. If the approach modeis not armed by 2 NM prior to the FAWP, the approachmode will not become active at 2 NM prior to theFAWP, and the equipment will flag. In theseconditions, the RAIM and CDI sensitivity will notramp down, and the pilot should not descend to MDA,but fly to the MAWP and execute a missed approach.The approach active annunciator and/or the receivershould be checked to ensure the approach mode isactive prior to the FAWP.

(8) Do not attempt to fly an approach unlessthe procedure in the onboard database is current andidentified as “GPS” on the approach chart. Thenavigation database may contain information aboutnon−overlay approach procedures that enhancesposition orientation generally by providing a map,

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while flying these approaches using conventionalNAVAIDs. This approach information should not beconfused with a GPS overlay approach (see thereceiver operating manual, AFM, or AFM Supple-ment for details on how to identify these proceduresin the navigation database). Flying point to point onthe approach does not assure compliance with thepublished approach procedure. The proper RAIMsensitivity will not be available and the CDIsensitivity will not automatically change to ±0.3NM. Manually setting CDI sensitivity does notautomatically change the RAIM sensitivity on somereceivers. Some existing non−precision approachprocedures cannot be coded for use with GPS and willnot be available as overlays.

(9) Pilots should pay particular attentionto the exact operation of their GPS receivers forperforming holding patterns and in the case ofoverlay approaches, operations such as procedureturns. These procedures may require manualintervention by the pilot to stop the sequencing ofwaypoints by the receiver and to resume automaticGPS navigation sequencing once the maneuver iscomplete. The same waypoint may appear in the routeof flight more than once consecutively (for example,IAWP, FAWP, MAHWP on a procedure turn). Caremust be exercised to ensure that the receiver issequenced to the appropriate waypoint for thesegment of the procedure being flown, especially ifone or more fly−overs are skipped (for example,FAWP rather than IAWP if the procedure turn is notflown). The pilot may have to sequence past one ormore fly−overs of the same waypoint in order to startGPS automatic sequencing at the proper place in thesequence of waypoints.

(10) Incorrect inputs into the GPS receiverare especially critical during approaches. In somecases, an incorrect entry can cause the receiver toleave the approach mode.

(11) A fix on an overlay approach identi-fied by a DME fix will not be in the waypointsequence on the GPS receiver unless there is apublished name assigned to it. When a name isassigned, the along track distance (ATD) to thewaypoint may be zero rather than the DME stated onthe approach chart. The pilot should be alert for thison any overlay procedure where the originalapproach used DME.

(12) If a visual descent point (VDP) ispublished, it will not be included in the sequence ofwaypoints. Pilots are expected to use normal pilotingtechniques for beginning the visual descent, such asATD.

(13) Unnamed stepdown fixes in the finalapproach segment may or may not be coded in thewaypoint sequence of the aircraft’s navigationdatabase and must be identified using ATD.Stepdown fixes in the final approach segment ofRNAV (GPS) approaches are being named, inaddition to being identified by ATD. However, GPSavionics may or may not accommodate waypointsbetween the FAF and MAP. Pilots must know thecapabilities of their GPS equipment and continue toidentify stepdown fixes using ATD when necessary.

(f) Missed Approach

(1) A GPS missed approach requires pilotaction to sequence the receiver past the MAWP to themissed approach portion of the procedure. The pilotmust be thoroughly familiar with the activationprocedure for the particular GPS receiver installed inthe aircraft and must initiate appropriate action afterthe MAWP. Activating the missed approach prior tothe MAWP will cause CDI sensitivity to immediatelychange to terminal (±1NM) sensitivity and thereceiver will continue to navigate to the MAWP. Thereceiver will not sequence past the MAWP. Turnsshould not begin prior to the MAWP. If the missedapproach is not activated, the GPS receiver willdisplay an extension of the inbound final approachcourse and the ATD will increase from the MAWPuntil it is manually sequenced after crossing theMAWP.

(2) Missed approach routings in which thefirst track is via a course rather than direct to the nextwaypoint require additional action by the pilot to setthe course. Being familiar with all of the inputsrequired is especially critical during this phase offlight.

(g) GPS NOTAMs/Aeronautical Informa-tion

(1) GPS satellite outages are issued asGPS NOTAMs both domestically and internation-ally. However, the effect of an outage on the intendedoperation cannot be determined unless the pilot has aRAIM availability prediction program which allowsexcluding a satellite which is predicted to be out ofservice based on the NOTAM information.

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(2) The terms UNRELIABLE and MAYNOT BE AVAILABLE are used in conjunction withGPS NOTAMs. Both UNRELIABLE and MAY NOTBE AVAILABLE are advisories to pilots indicatingthe expected level of service may not be available.UNRELIABLE does not mean there is a problemwith GPS signal integrity. If GPS service is available,pilots may continue operations. If the LNAV orLNAV/VNAV service is available, pilots may use thedisplayed level of service to fly the approach. GPSoperation may be NOTAMed UNRELIABLE orMAY NOT BE AVAILABLE due to testing oranomalies. (Pilots are encouraged to report GPSanomalies, including degraded operation and/or lossof service, as soon as possible, reference paragraph1−1−13.) When GPS testing NOTAMS are publishedand testing is actually occurring, Air Traffic Controlwill advise pilots requesting or cleared for a GPS orRNAV (GPS) approach that GPS may not beavailable and request intentions. If pilots havereported GPS anomalies, Air Traffic Control willrequest the pilot’s intentions and/or clear the pilot foran alternate approach, if available and operational.

EXAMPLE−The following is an example of a GPS testing NOTAM: !GPS 06/001 ZAB NAV GPS (INCLUDING WAAS, GBAS,AND ADS-B) MAY NOT BE AVAILABLE WITHIN A468NM RADIUS CENTERED AT 330702N1062540W(TCS 093044) FL400-UNL DECREASING IN AREAWITH A DECREASE IN ALTITUDE DEFINED AS:425NM RADIUS AT FL250, 360NM RADIUS AT10000FT, 354NM RADIUS AT 4000FT AGL, 327NMRADIUS AT 50FT AGL. 1406070300-1406071200.

(3) Civilian pilots may obtain GPS RAIMavailability information for non−precision approachprocedures by using a manufacturer-supplied RAIMprediction tool, or using the Service AvailabilityPrediction Tool (SAPT) on the FAA en route andterminal RAIM prediction website. Pilots can alsorequest GPS RAIM aeronautical information from aflight service station during preflight briefings. GPSRAIM aeronautical information can be obtained fora period of 3 hours (for example, if you are scheduledto arrive at 1215 hours, then the GPS RAIMinformation is available from 1100 to 1400 hours) ora 24−hour timeframe at a particular airport. FAAbriefers will provide RAIM information for a periodof 1 hour before to 1 hour after the ETA hour, unlessa specific timeframe is requested by the pilot. If flyinga published GPS departure, a RAIM predictionshould also be requested for the departure airport.

(4) The military provides airfield specificGPS RAIM NOTAMs for non−precision approachprocedures at military airfields. The RAIM outagesare issued as M−series NOTAMs and may be obtainedfor up to 24 hours from the time of request.

(5) Receiver manufacturers and/or data-base suppliers may supply “NOTAM” typeinformation concerning database errors. Pilotsshould check these sources, when available, to ensurethat they have the most current informationconcerning their electronic database.

(h) Receiver Autonomous Integrity Moni-toring (RAIM)

(1) RAIM outages may occur due to aninsufficient number of satellites or due to unsuitablesatellite geometry which causes the error in theposition solution to become too large. Loss of satellitereception and RAIM warnings may occur due toaircraft dynamics (changes in pitch or bank angle).Antenna location on the aircraft, satellite positionrelative to the horizon, and aircraft attitude may affectreception of one or more satellites. Since the relativepositions of the satellites are constantly changing,prior experience with the airport does not guaranteereception at all times, and RAIM availability shouldalways be checked.

(2) If RAIM is not available, use anothertype of navigation and approach system, selectanother route or destination, or delay the trip untilRAIM is predicted to be available on arrival. Onlonger flights, pilots should consider rechecking theRAIM prediction for the destination during the flight.This may provide an early indication that anunscheduled satellite outage has occurred sincetakeoff.

(3) If a RAIM failure/status annunciationoccurs pr ior to the f inal approach waypoint(FAWP), the approach should not be completed sinceGPS no longer provides the required integrity. Thereceiver performs a RAIM prediction by 2 NM priorto the FAWP to ensure that RAIM is available as acondition for entering the approach mode. The pilotshould ensure the receiver has sequenced from“Armed” to “Approach” prior to the FAWP (normallyoccurs 2 NM prior). Failure to sequence may be anindication of the detection of a satellite anomaly,failure to arm the receiver (if required), or otherproblems which preclude flying the approach.

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(4) If the receiver does not sequence intothe approach mode or a RAIM failure/statusannunciation occurs prior to the FAWP, the pilot mustnot initiate the approach or descend, but insteadproceed to the missed approach waypoint ( MAWP)via the FAWP, perform a missed approach, andcontact ATC as soon as practical. The GPS receivermay continue to operate after a RAIM flag/statusannunciation appears, but the navigation informationshould be considered advisory only. Refer to thereceiver operating manual for specific indicationsand instructions associated with loss of RAIM priorto the FAF.

(5) If the RAIM flag/status annunciationappears after the FAWP, the pilot should initiate aclimb and execute the missed approach. The GPSreceiver may continue to operate after a RAIMflag/status annunciation appears, but the navigationinformation should be considered advisory only.Refer to the receiver operating manual for operatingmode information during a RAIM annunciation.

(i) Waypoints

(1) GPS receivers navigate from onedefined point to another retrieved from the aircraft’sonboard navigational database. These points arewaypoints (5-letter pronounceable name), existingVHF intersections, DME fixes with 5−letterpronounceable names and 3-letter NAVAID IDs.Each waypoint is a geographical location defined bya latitude/longitude geographic coordinate. These5−letter waypoints, VHF intersections, 5−letterpronounceable DME fixes and 3−letter NAVAID IDsare published on various FAA aeronautical naviga-tion products (IFR Enroute Charts, VFR Charts,Terminal Procedures Publications, etc.).

(2) A Computer Navigation Fix (CNF) isalso a point defined by a latitude/longitude coordinateand is required to support Performance−BasedNavigation (PBN) operations. The GPS receiver usesCNFs in conjunction with waypoints to navigate frompoint to point. However, CNFs are not recognized byATC. ATC does not maintain CNFs in their databaseand they do not use CNFs for any air traffic controlpurpose. CNFs may or may not be charted on FAAaeronautical navigation products, are listed in thechart legends, and are for advisory purposes only.

Pilots are not to use CNFs for point to pointnavigation (proceed direct), filing a flight plan, or inaircraft/ATC communications. CNFs that do appearon aeronautical charts allow pilots increasedsituational awareness by identifying points in theaircraft database route of flight with points on theaeronautical chart. CNFs are random five-letteridentifiers, not pronounceable like waypoints andplaced in parenthesis. Eventually, all CNFs will beginwith the letters “CF” followed by three consonants(for example, CFWBG). This five-letter identifierwill be found next to an “x” on enroute charts andpossibly on an approach chart. On instrumentapproach procedures (charts) in the terminalprocedures publication, CNFs may represent un-named DME fixes, beginning and ending points ofDME arcs, and sensor (ground-based signal i.e.,VOR, NDB, ILS) final approach fixes on GPSoverlay approaches. These CNFs provide the GPSwith points on the procedure that allow the overlayapproach to mirror the ground-based sensorapproach. These points should only be used by theGPS system for navigation and should not be used bypilots for any other purpose on the approach. TheCNF concept has not been adopted or recognized bythe International Civil Aviation Organization(ICAO).

(3) GPS approaches use fly−over andfly−by waypoints to join route segments on anapproach. Fly−by waypoints connect the twosegments by allowing the aircraft to turn prior to thecurrent waypoint in order to roll out on course to thenext waypoint. This is known as turn anticipation andis compensated for in the airspace and terrainclearances. The MAWP and the missed approachholding waypoint (MAHWP) are normally the onlytwo waypoints on the approach that are not fly−bywaypoints. Fly−over waypoints are used when theaircraft must overfly the waypoint prior to starting aturn to the new course. The symbol for a fly-overwaypoint is a circled waypoint. Some waypoints mayhave dual use; for example, as a fly−by waypointwhen used as an IF for a NoPT route and as a fly-overwaypoint when the same waypoint is also used as anIAF/IF hold-in-lieu of PT. When this occurs, the lessrestrictive (fly-by) symbology will be charted.Overlay approach charts and some early stand−aloneGPS approach charts may not reflect this convention.

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(4) Unnamed waypoints for each airportwill be uniquely identified in the database. Althoughthe identifier may be used at different airports (forexample, RW36 will be the identifier at each airportwith a runway 36), the actual point, at each airport, isdefined by a specific latitude/longitude coordinate.

(5) The runway threshold waypoint, nor-mally the MAWP, may have a five−letter identifier(for example, SNEEZ) or be coded as RW## (forexample, RW36, RW36L). MAWPs located at therunway threshold are being changed to the RW##identifier, while MAWPs not located at the thresholdwill have a five−letter identifier. This may cause theapproach chart to differ from the aircraft databaseuntil all changes are complete. The runway thresholdwaypoint is also used as the center of the MinimumSafe Altitude (MSA) on most GPS approaches.

(j) Position Orientation.

Pilots should pay particular attention to positionorientation while using GPS. Distance and trackinformation are provided to the next activewaypoint, not to a fixed navigation aid. Receiversmay sequence when the pilot is not flying along anactive route, such as when being vectored ordeviating for weather, due to the proximity to anotherwaypoint in the route. This can be prevented byplacing the receiver in the non-sequencing mode.When the receiver is in the non-sequencing mode,bearing and distance are provided to the selectedwaypoint and the receiver will not sequence to thenext waypoint in the route until placed back in theauto sequence mode or the pilot selects a differentwaypoint. The pilot may have to compute the ATDto stepdown fixes and other points on overlayapproaches, due to the receiver showing ATD to thenext waypoint rather than DME to the VOR or ILSground station.

(k) Impact of Magnetic Variation on PBNSystems

(1) Differences may exist between PBNsystems and the charted magnetic courses onground−based NAVAID instrument flight procedures(IFP), enroute charts, approach charts, and StandardInstrument Departure/Standard Terminal Arrival(SID/STAR) charts. These differences are due to themagnetic variance used to calculate the magnetic

course. Every leg of an instrument procedure is firstcomputed along a desired ground track with referenceto true north. A magnetic variation correction is thenapplied to the true course in order to calculate amagnetic course for publication. The type ofprocedure will determine what magnetic variationvalue is added to the true course. A ground−basedNAVAID IFP applies the facility magnetic variationof record to the true course to get the charted magneticcourse. Magnetic courses on PBN procedures arecalculated two different ways. SID/STAR proceduresuse the airport magnetic variation of record, whileIFR enroute charts use magnetic reference bearing.PBN systems make a correction to true north byadding a magnetic variation calculated with analgorithm based on aircraft position, or by adding themagnetic variation coded in their navigationaldatabase. This may result in the PBN system and theprocedure designer using a different magneticvariation, which causes the magnetic coursedisplayed by the PBN system and the magnetic coursecharted on the IFP plate to be different. It is importantto understand, however, that PBN systems, (with theexception of VOR/DME RNAV equipment) navigateby reference to true north and display magneticcourse only for pilot reference. As such, a properlyfunctioning PBN system, containing a current andaccurate navigational database, should fly thecorrect ground track for any loaded instrumentprocedure, despite differences in displayed magneticcourse that may be attributed to magnetic variationapplication. Should significant differences betweenthe approach chart and the PBN system avionics’application of the navigation database arise, thepublished approach chart, supplemented by NOT-AMs, holds precedence.

(2) The course into a waypoint may notalways be 180 degrees different from the courseleaving the previous waypoint, due to the PBNsystem avionics’ computation of geodesic paths,distance between waypoints, and differences inmagnetic variation application. Variations indistances may also occur since PBN systemdistance−to−waypoint values are ATDs computed tothe next waypoint and the DME values published onunderlying procedures are slant−range distancesmeasured to the station. This difference increaseswith aircraft altitude and proximity to the NAVAID.

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(l) GPS Familiarization

Pilots should practice GPS approaches in visualmeteorological conditions (VMC) until thoroughlyproficient with all aspects of their equipment(receiver and installation) prior to attempting flightin instrument meteorological conditions (IMC).Pilots should be proficient in the following areas:

(1) Using the receiver autonomous integ-rity monitoring (RAIM) prediction function;

(2) Inserting a DP into the flight plan,including setting terminal CDI sensitivity, if required,and the conditions under which terminal RAIM isavailable for departure;

(3) Programming the destination airport;

(4) Programming and flying the ap-proaches (especially procedure turns and arcs);

(5) Changing to another approach afterselecting an approach;

(6) Programming and flying “direct”missed approaches;

(7) Programming and flying “routed”missed approaches;

(8) Entering, flying, and exiting holdingpatterns, particularly on approaches with a secondwaypoint in the holding pattern;

(9) Programming and flying a “route” froma holding pattern;

(10) Programming and flying an approachwith radar vectors to the intermediate segment;

(11) Indication of the actions required forRAIM failure both before and after the FAWP; and

(12) Programming a radial and distancefrom a VOR (often used in departure instructions).

TBL 1−1−5

GPS IFR Equipment Classes/Categories

TSO−C129

EquipmentClass RAIM

Int. Nav. Sys. toProv. RAIM

Equiv.Oceanic En Route Terminal

Non−precisionApproachCapable

Class A − GPS sensor and navigation capability.

A1 yes yes yes yes yes

A2 yes yes yes yes no

Class B − GPS sensor data to an integrated navigation system (i.e., FMS, multi−sensor navigation system, etc.).

B1 yes yes yes yes yes

B2 yes yes yes yes no

B3 yes yes yes yes yes

B4 yes yes yes yes no

Class C − GPS sensor data to an integrated navigation system (as in Class B) which provides enhanced guidance to an autopilot, orflight director, to reduce flight tech. errors. Limited to 14 CFR Part 121 or equivalent criteria.

C1 yes yes yes yes yes

C2 yes yes yes yes no

C3 yes yes yes yes yes

C4 yes yes yes yes no

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TBL 1−1−6

GPS Approval Required/Authorized Use

EquipmentType1

InstallationApprovalRequired

OperationalApprovalRequired

IFR En Route2

IFRTerminal2

IFR Approach3

Oceanic Remote

In Lieu ofADF and/or

DME3

Hand held4 X5

VFR Panel Mount4 X

IFR En Routeand Terminal

X X X X X

IFR Oceanic/Remote

X X X X X X

IFR En Route,Terminal, and

Approach

X X X X X X

NOTE−1To determine equipment approvals and limitations, refer to the AFM, AFM supplements, or pilot guides.2Requires verification of data for correctness if database is expired.3Requires current database or verification that the procedure has not been amended since the expiration of the database.4VFR and hand−held GPS systems are not authorized for IFR navigation, instrument approaches, or as a primary instrumentflight reference. During IFR operations they may be considered only an aid to situational awareness.5Hand−held receivers require no approval. However, any aircraft modification to support the hand−held receiver;i.e., installation of an external antenna or a permanent mounting bracket, does require approval.

1−1−18. Wide Area Augmentation System(WAAS)

a. General

1. The FAA developed the WAAS to improvethe accuracy, integrity and availability of GPSsignals. WAAS will allow GPS to be used, as theaviation navigation system, from takeoff throughapproach when it is complete. WAAS is a criticalcomponent of the FAA’s strategic objective for aseamless satellite navigation system for civilaviation, improving capacity and safety.

2. The International Civil Aviation Organiza-tion (ICAO) has defined Standards andRecommended Practices (SARPs) for satellite−basedaugmentation systems (SBAS) such as WAAS.Japan, India, and Europe are building similarsystems: EGNOS, the European GeostationaryNavigation Overlay System; India’s GPS andGeo-Augmented Navigation (GAGAN) system; andJapan’s Multi-functional Transport Satellite (MT-SAT)-based Satellite Augmentation System(MSAS). The merging of these systems will create anexpansive navigation capability similar to GPS, butwith greater accuracy, availability, and integrity.

3. Unlike traditional ground−based navigationaids, WAAS will cover a more extensive service area.Precisely surveyed wide−area reference stations(WRS) are linked to form the U.S. WAAS network.Signals from the GPS satellites are monitored bythese WRSs to determine satellite clock andephemeris corrections and to model the propagationeffects of the ionosphere. Each station in the networkrelays the data to a wide−area master station (WMS)where the correction information is computed. Acorrection message is prepared and uplinked to ageostationary earth orbit satellite (GEO) via a GEOuplink subsystem (GUS) which is located at theground earth station (GES). The message is thenbroadcast on the same frequency as GPS (L1,1575.42 MHz) to WAAS receivers within thebroadcast coverage area of the WAAS GEO.

4. In addition to providing the correction signal,the WAAS GEO provides an additional pseudorangemeasurement to the aircraft receiver, improving theavailability of GPS by providing, in effect, anadditional GPS satellite in view. The integrity of GPSis improved through real−time monitoring, and theaccuracy is improved by providing differentialcorrections to reduce errors. The performance

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improvement is sufficient to enable approachprocedures with GPS/WAAS glide paths (verticalguidance).

5. The FAA has completed installation of 3GEO satellite links, 38 WRSs, 3 WMSs, 6 GES, andthe required terrestrial communications to supportthe WAAS network including 2 operational controlcenters. Prior to the commissioning of the WAAS forpublic use, the FAA conducted a series of test andvalidation activities. Future dual frequency opera-tions are planned.

6. GNSS navigation, including GPS andWAAS, is referenced to the WGS−84 coordinatesystem. It should only be used where the AeronauticalInformation Publications (including electronic dataand aeronautical charts) conform to WGS−84 orequivalent. Other countries’ civil aviation authoritiesmay impose additional limitations on the use of theirSBAS systems.

b. Instrument Approach Capabilities

1. A class of approach procedures whichprovide vertical guidance, but which do not meet theICAO Annex 10 requirements for precision ap-proaches has been developed to support satellitenavigation use for aviation applications worldwide.These procedures are not precision and are referred toas Approach with Vertical Guidance (APV), aredefined in ICAO Annex 6, and include approachessuch as the LNAV/VNAV and localizer performancewith vertical guidance (LPV). These approachesprovide vertical guidance, but do not meet the morestringent standards of a precision approach. Properlycertified WAAS receivers will be able to fly to LPVminima and LNAV/VNAV minima, using a WAASelectronic glide path, which eliminates the errors thatcan be introduced by using Barometric altimetry.

2. LPV minima takes advantage of the highaccuracy guidance and increased integrity providedby WAAS. This WAAS generated angular guidanceallows the use of the same TERPS approach criteriaused for ILS approaches. LPV minima may have adecision altitude as low as 200 feet height abovetouchdown with visibility minimums as low as 1/2mile, when the terrain and airport infrastructuresupport the lowest minima. LPV minima is publishedon the RNAV (GPS) approach charts (see Paragraph5−4−5, Instrument Approach Procedure Charts).

3. A different WAAS-based line of minima,called Localizer Performance (LP) is being added inlocations where the terrain or obstructions do notallow publication of vertically guided LPV minima.LP takes advantage of the angular lateral guidanceand smaller position errors provided by WAAS toprovide a lateral only procedure similar to an ILSLocalizer. LP procedures may provide lower minimathan a LNAV procedure due to the narrower obstacleclearance surface.

NOTE−WAAS receivers certified prior to TSO−C145b andTSO−C146b, even if they have LPV capability, do notcontain LP capability unless the receiver has beenupgraded. Receivers capable of flying LP procedures mustcontain a statement in the Aircraft Flight Manual (AFM),AFM Supplement, or Approved Supplemental FlightManual stating that the receiver has LP capability, as wellas the capability for the other WAAS and GPS approachprocedure types.

4. WAAS provides a level of service thatsupports all phases of flight, including RNAV (GPS)approaches to LNAV, LP, LNAV/VNAV, and LPVlines of minima, within system coverage. Somelocations close to the edge of the coverage may havea lower availability of vertical guidance.

c. General Requirements

1. WAAS avionics must be certified inaccordance with Technical Standard Order (TSO)TSO−C145(), Airborne Navigation Sensors Usingthe (GPS) Augmented by the Wide Area Augmenta-tion System (WAAS); or TSO−C146(), Stand−AloneAirborne Navigation Equipment Using the GlobalPositioning System (GPS) Augmented by the WideArea Augmentation System (WAAS), and installed inaccordance with AC 20−138, Airworthiness Ap-proval of Positioning and Navigation Systems.

2. GPS/WAAS operation must be conducted inaccordance with the FAA−approved aircraft flightmanual (AFM) and flight manual supplements. Flightmanual supplements will state the level of approachprocedure that the receiver supports. IFR approvedWAAS receivers support all GPS only operations aslong as lateral capability at the appropriate level isfunctional. WAAS monitors both GPS and WAASsatellites and provides integrity.

3. GPS/WAAS equipment is inherently capableof supporting oceanic and remote operations if theoperator obtains a fault detection and exclusion(FDE) prediction program.

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4. Air carrier and commercial operators mustmeet the appropriate provisions of their approvedoperations specifications.

5. Prior to GPS/WAAS IFR operation, the pilotmust review appropriate Notices to Airmen (NOT-AMs) and aeronautical information. Thisinformation is available on request from a FlightService Station. The FAA will provide NOTAMs toadvise pilots of the status of the WAAS and level ofservice available.

(a) The term MAY NOT BE AVBL is used inconjunction with WAAS NOTAMs and indicates thatdue to ionospheric conditions, lateral guidance maystill be available when vertical guidance isunavailable. Under certain conditions, both lateraland vertical guidance may be unavailable. ThisNOTAM language is an advisory to pilots indicatingthe expected level of WAAS service (LNAV/VNAV,LPV, LP) may not be available.

EXAMPLE−!FDC FDC NAV WAAS VNAV/LPV/LP MINIMA MAYNOT BE AVBL 1306111330-1306141930EST or !FDC FDC NAV WAAS VNAV/LPV MINIMA NOT AVBL,WAAS LP MINIMA MAY NOT BE AVBL1306021200-1306031200EST

WAAS MAY NOT BE AVBL NOTAMs arepredictive in nature and published for flight planningpurposes. Upon commencing an approach atlocations NOTAMed WAAS MAY NOT BE AVBL,if the WAAS avionics indicate LNAV/VNAV or LPVservice is available, then vertical guidance may beused to complete the approach using the displayedlevel of service. Should an outage occur during theapproach, reversion to LNAV minima or an alternateinstrument approach procedure may be required.When GPS testing NOTAMS are published andtesting is actually occurring, Air Traffic Control willadvise pilots requesting or cleared for a GPS orRNAV (GPS) approach that GPS may not beavailable and request intentions. If pilots havereported GPS anomalies, Air Traffic Control willrequest the pilot’s intentions and/or clear the pilot foran alternate approach, if available and operational.

(b) WAAS area-wide NOTAMs are origin-ated when WAAS assets are out of service and impactthe service area. Area−wide WAAS NOT AVAIL-ABLE (AVBL) NOTAMs indicate loss ormalfunction of the WAAS system. In flight, Air

Traffic Control will advise pilots requesting a GPS orRNAV (GPS) approach of WAAS NOT AVBLNOTAMs if not contained in the ATIS broadcast.

EXAMPLE−For unscheduled loss of signal or service, an exampleNOTAM is: !FDC FDC NAV WAAS NOT AVBL1311160600− 1311191200EST. For scheduled loss of signal or service, an exampleNOTAM is: !FDC FDC NAV WAAS NOT AVBL1312041015- 1312082000EST.

(c) Site−specific WAAS MAY NOT BEAVBL NOTAMs indicate an expected level ofservice; for example, LNAV/VNAV, LP, or LPV maynot be available. Pilots must request site−specificWAAS NOTAMs during flight planning. In flight,Air Traffic Control will not advise pilots of WAASMAY NOT BE AVBL NOTAMs.

NOTE−Though currently unavailable, the FAA is updating itsprediction tool software to provide this site-service in thefuture.

(d) Most of North America has redundantcoverage by two or more geostationary satellites. Oneexception is the northern slope of Alaska. If there isa problem with the satellite providing coverage to thisarea, a NOTAM similar to the following example willbe issued:

EXAMPLE−!FDC 4/3406 (PAZA A0173/14) ZAN NAV WAAS SIGNALMAY NOT BE AVBL NORTH OF LINE FROM7000N150000W TO 6400N16400W. RMK WAAS USERSSHOULD CONFIRM RAIM AVAILABILITY FOR IFROPERATIONS IN THIS AREA. T-ROUTES IN THISSECTOR NOT AVBL. ANY REQUIRED ALTERNATEAIRPORT IN THIS AREA MUST HAVE AN APPROVEDINSTRUMENT APPROACH PROCEDURE OTHERTHAN GPS THAT IS ANTICIPATED TO BE OPERA-TIONAL AND AVAILABLE AT THE ESTIMATED TIMEOF ARRIVAL AND WHICH THE AIRCRAFT ISEQUIPPED TO FLY. 1406030812-1406050812EST .

6. When GPS−testing NOTAMS are publishedand testing is actually occurring, Air Traffic Controlwill advise pilots requesting or cleared for a GPS orRNAV (GPS) approach that GPS may not beavailable and request intentions. If pilots havereported GPS anomalies, Air Traffic Control willrequest the pilot’s intentions and/or clear the pilot foran alternate approach, if available and operational.

EXAMPLE−Here is an example of a GPS testing NOTAM: !GPS 06/001 ZAB NAV GPS (INCLUDING WAAS, GBAS,

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AND ADS-B) MAY NOT BE AVAILABLE WITHIN A468NM RADIUS CENTERED AT 330702N1062540W(TCS 093044) FL400-UNL DECREASING IN AREAWITH A DECREASE IN ALTITUDE DEFINED AS:425NM RADIUS AT FL250, 360NM RADIUS AT10000FT, 354NM RADIUS AT 4000FT AGL, 327NMRADIUS AT 50FT AGL. 1406070300-1406071200.

7. When the approach chart is annotated withthe symbol, site−specific WAAS MAY NOT BEAVBL NOTAMs or Air Traffic advisories are notprovided for outages in WAAS LNAV/VNAV andLPV vertical service. Vertical outages may occurdaily at these locations due to being close to the edgeof WAAS system coverage. Use LNAV or circlingminima for flight planning at these locations, whetheras a destination or alternate. For flight operations atthese locations, when the WAAS avionics indicatethat LNAV/VNAV or LPV service is available, thenthe vertical guidance may be used to complete theapproach using the displayed level of service. Shouldan outage occur during the procedure, reversion toLNAV minima may be required.

NOTE−Area−wide WAAS NOT AVBL NOTAMs apply to allairports in the WAAS NOT AVBL area designated in theNOTAM, including approaches at airports where anapproach chart is annotated with the symbol.

8. GPS/WAAS was developed to be used withinGEO coverage over North America without the needfor other radio navigation equipment appropriate tothe route of flight to be flown. Outside the WAAScoverage or in the event of a WAAS failure,GPS/WAAS equipment reverts to GPS−only opera-tion and satisfies the requirements for basic GPSequipment. (See paragraph 1−1−17 for theserequirements).

9. Unlike TSO−C129 avionics, which werecertified as a supplement to other means ofnavigation, WAAS avionics are evaluated withoutreliance on other navigation systems. As such,installation of WAAS avionics does not require theaircraft to have other equipment appropriate to theroute to be flown. (See paragraph 1−1−17 d for moreinformation on equipment requirements.)

(a) Pilots with WAAS receivers may flightplan to use any instrument approach procedureauthorized for use with their WAAS avionics asthe planned approach at a required alternate, withthe following restrictions. When using WAAS at

an alternate airport, flight planning must be basedon flying the RNAV (GPS) LNAV or circling minimaline, or minima on a GPS approach procedure, orconventional approach procedure with “or GPS” inthe title. Code of Federal Regulation (CFR) Part 91non−precision weather requirements must be used forplanning. Upon arrival at an alternate, when theWAAS navigation system indicates that LNAV/VNAV or LPV service is available, then verticalguidance may be used to complete the approach usingthe displayed level of service. The FAA has begunremoving the NA (Alternate Minimums NotAuthorized) symbol from select RNAV (GPS) andGPS approach procedures so they may be used byapproach approved WAAS receivers at alternateairports. Some approach procedures will still requirethe NA for other reasons, such as no weatherreporting, so it cannot be removed from allprocedures. Since every procedure must be individu-ally evaluated, removal of the NA from RNAV(GPS) and GPS procedures will take some time.

NOTE−Properly trained and approved, as required, TSO-C145()and TSO-C146() equipped users (WAAS users) with andusing approved baro-VNAV equipment may plan forLNAV/VNAV DA at an alternate airport. Specificallyauthorized WAAS users with and using approvedbaro-VNAV equipment may also plan for RNP 0.3 DA at thealternate airport as long as the pilot has verified RNPavailability through an approved prediction program.

d. Flying Procedures with WAAS

1. WAAS receivers support all basic GPSapproach functions and provide additional capabilit-ies. One of the major improvements is the ability togenerate glide path guidance, independent of groundequipment or barometric aiding. This eliminatesseveral problems such as hot and cold temperatureeffects, incorrect altimeter setting, or lack of a localaltimeter source. It also allows approach proceduresto be built without the cost of installing groundstations at each airport or runway. Some approachcertified receivers may only generate a glide pathwith performance similar to Baro−VNAV and areonly approved to fly the LNAV/VNAV line of minimaon the RNAV (GPS) approach charts. Receivers withadditional capability (including faster update ratesand smaller integrity limits) are approved to fly theLPV line of minima. The lateral integrity changesdramatically from the 0.3 NM (556 meter) limit forGPS, LNAV, and LNAV/VNAV approach mode, to

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40 meters for LPV. It also provides vertical integritymonitoring, which bounds the vertical error to 50meters for LNAV/VNAV and LPVs with minima of250’ or above, and bounds the vertical error to 35meters for LPVs with minima below 250’.

2. When an approach procedure is selected andactive, the receiver will notify the pilot of the mostaccurate level of service supported by the combina-tion of the WAAS signal, the receiver, and theselected approach, using the naming conventions onthe minima lines of the selected approach procedure.For example, if an approach is published with LPVminima and the receiver is only certified forLNAV/VNAV, the equipment would indicate“LNAV/VNAV available,” even though the WAASsignal would support LPV. If flying an existingLNAV/VNAV procedure with no LPV minima, thereceiver will notify the pilot “LNAV/VNAVavailable,” even if the receiver is certified for LPVand the signal supports LPV. If the signal does notsupport vertical guidance on procedures with LPVand/or LNAV/VNAV minima, the receiver annunci-ation will read “LNAV available.” On lateral onlyprocedures with LP and LNAV minima the receiverwill indicate “LP available” or “LNAV available”based on the level of lateral service available. Oncethe level of service notification has been given, thereceiver will operate in this mode for the duration ofthe approach procedure, unless that level of servicebecomes unavailable. The receiver cannot changeback to a more accurate level of service until the nexttime an approach is activated.

NOTE−Receivers do not “fail down” to lower levels of serviceonce the approach has been activated. If only thevertical off flag appears, the pilot may elect to use theLNAV minima if the rules under which the flight isoperating allow changing the type of approach being flownafter commencing the procedure. If the lateral integritylimit is exceeded on an LP approach, a missed approachwill be necessary since there is no way to reset the lateralalarm limit while the approach is active.

3. Another additional feature of WAAS receiv-ers is the ability to exclude a bad GPS signal andcontinue operating normally. This is normallyaccomplished by the WAAS correction information.Outside WAAS coverage or when WAAS is notavailable, it is accomplished through a receiveralgorithm called FDE. In most cases this operationwill be invisible to the pilot since the receiver will

continue to operate with other available satellitesafter excluding the “bad” signal. This capabilityincreases the reliability of navigation.

4. Both lateral and vertical scaling for theLNAV/VNAV and LPV approach procedures aredifferent than the linear scaling of basic GPS. Whenthe complete published procedure is flown, ±1 NMlinear scaling is provided until two (2) NM prior to theFAF, where the sensitivity increases to be similar tothe angular scaling of an ILS. There are two differ-ences in the WAAS scaling and ILS: 1) on long finalapproach segments, the initial scaling will be±0.3 NM to achieve equivalent performance to GPS(and better than ILS, which is less sensitive far fromthe runway); 2) close to the runway threshold, thescaling changes to linear instead of continuing tobecome more sensitive. The width of the finalapproach course is tailored so that the total width isusually 700 feet at the runway threshold. Since theorigin point of the lateral splay for the angular portionof the final is not fixed due to antenna placement likelocalizer, the splay angle can remain fixed, making aconsistent width of final for aircraft being vectoredonto the final approach course on different lengthrunways. When the complete published procedure isnot flown, and instead the aircraft needs to capture theextended final approach course similar to ILS, thevector to final (VTF) mode is used. Under VTF, thescaling is linear at ±1 NM until the point where theILS angular splay reaches a width of ±1 NMregardless of the distance from the FAWP.

5. The WAAS scaling is also different than GPSTSO−C129() in the initial portion of the missedapproach. Two differences occur here. First, thescaling abruptly changes from the approach scaling tothe missed approach scaling, at approximately thedeparture end of the runway or when the pilot selectsmissed approach guidance rather than ramping asGPS does. Second, when the first leg of the missedapproach is a Track to Fix (TF) leg aligned within 3degrees of the inbound course, the receiver willchange to 0.3 NM linear sensitivity until the turninitiation point for the first waypoint in the missedapproach procedure, at which time it will abruptlychange to terminal (±1 NM) sensitivity. This allowsthe elimination of close in obstacles in the early partof the missed approach that may otherwise cause theDA to be raised.

6. There are two ways to select the finalapproach segment of an instrument approach. Most

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receivers use menus where the pilot selects theairport, the runway, the specific approach procedureand finally the IAF, there is also a channel numberselection method. The pilot enters a unique 5−digitnumber provided on the approach chart, and thereceiver recalls the matching final approach segmentfrom the aircraft database. A list of informationincluding the available IAFs is displayed and the pilotselects the appropriate IAF. The pilot should confirmthat the correct final approach segment was loaded bycross checking the Approach ID, which is alsoprovided on the approach chart.

7. The Along−Track Distance (ATD) during thefinal approach segment of an LNAV procedure (witha minimum descent altitude) will be to the MAWP. OnLNAV/VNAV and LPV approaches to a decisionaltitude, there is no missed approach waypoint so thealong−track distance is displayed to a point normallylocated at the runway threshold. In most cases, theMAWP for the LNAV approach is located on therunway threshold at the centerline, so these distanceswill be the same. This distance will always varyslightly from any ILS DME that may be present, sincethe ILS DME is located further down the runway.Initiation of the missed approach on the LNAV/VNAV and LPV approaches is still based on reachingthe decision altitude without any of the items listed in14 CFR Section 91.175 being visible, and must not bedelayed while waiting for the ATD to reach zero. TheWAAS receiver, unlike a GPS receiver, willautomatically sequence past the MAWP if the missedapproach procedure has been designed for RNAV.The pilot may also select missed approach prior to theMAWP; however, navigation will continue to theMAWP prior to waypoint sequencing taking place.

1−1−19. Ground Based AugmentationSystem (GBAS) Landing System (GLS)

a. General1. The GLS provides precision navigation

guidance for exact alignment and descent of aircrafton approach to a runway. GBAS equipment provideslocalized differential augmentation to the GlobalPositioning System (GPS).

NOTE−To remain consistent with international terminology, theFAA will use the term GBAS in place of the former termLocal Area Augmentation System (LAAS).

2. GLS displays three−dimension vertical andhorizontal navigation guidance to the pilot much like

ILS. GLS navigation is based on GPS signalsaugmented by position correction, integrity parame-ters, and approach path definition informationtransmitted over VHF from the local GBAS groundstation. One GBAS station can support multiple GLSprecision approaches to nearby runways within theGBAS’s maximum use distance.

3. GLS provides guidance similar to ILSapproaches for the final approach segment, thoughthe approach service volume has different dimen-sions (see FIG 1−1−8). The GLS approach isconstructed using the RNP approach (RNP APCH)navigation specification, and may include vertically−guided turn(s) after the IAF or on the missed approachprocedure. Portions of the approach prior to an IAFand after the final approach segment may also requireArea Navigation (RNAV) typically using theRequired Navigation Performance 1 (RNP 1)navigation specification. See paragraph 1−2−1 formore information on navigation specifications.

4. GLS consists of a GBAS Ground Facility(GGF), at least four ground reference stations, acorrections processor, a VHF Data Broadcast (VDB)uplink antenna, an aircraft GBAS receiver, and acharted instrument approach procedure.

b. Procedure

1. Pilots will select the five digit GBAS channelnumber of the associated GLS approach within theFlight Management System (FMS) menu ormanually select the five digits (system dependent).Selection of the GBAS channel number also tunes theVDB.

2. Following procedure selection, confirmationthat the correct GLS procedure is loaded can beaccomplished by cross checking the chartedReference Path Indicator (RPI) or approach ID withthe cockpit displayed RPI or audio identification ofthe RPI with Morse Code (for some systems).Distance to the runway threshold will be displayed tothe pilot once the aircraft is inside the approachservice volume.

3. The pilot will fly the GLS approach usingmany of the same techniques as ILS including usinga heading or lateral steering mode to intercept theGLS final approach course and then switching to theappropriate approach navigation mode once theaircraft is within the approach service volume andprior to the glide path intercept point. See also theInstrument Procedures Handbook for more informa-tion on GLS.

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FIG 1−1−8

GLS Standard Approach Service Volume

1−1−20. Precision Approach Systems otherthan ILS and GLS

a. General

Approval and use of precision approach systemsother than ILS and GLS require the issuance ofspecial instrument approach procedures.

b. Special Instrument Approach Procedure

1. Special instrument approach proceduresmust be issued to the aircraft operator if pilot training,aircraft equipment, and/or aircraft performance isdifferent than published procedures. Special instru-ment approach procedures are not distributed forgeneral public use. These procedures are issued to anaircraft operator when the conditions for operationsapproval are satisfied.

2. General aviation operators requesting ap-proval for special procedures should contact the localFlight Standards District Office to obtain a letter ofauthorization. Air carrier operators requestingapproval for use of special procedures should contacttheir Certificate Holding District Office for authoriz-ation through their Operations Specification.

c. Transponder Landing System (TLS)

1. The TLS is designed to provide approachguidance utilizing existing airborne ILS localizer,glide slope, and transponder equipment.

2. Ground equipment consists of a transponderinterrogator, sensor arrays to detect lateral andvertical position, and ILS frequency transmitters. TheTLS detects the aircraft’s position by interrogating itstransponder. It then broadcasts ILS frequency signalsto guide the aircraft along the desired approach path.

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3. TLS instrument approach procedures aredesignated Special Instrument Approach Procedures.Special aircrew training is required. TLS groundequipment provides approach guidance for only oneaircraft at a time. Even though the TLS signal isreceived using the ILS receiver, no fixed course orglidepath is generated. The concept of operation isvery similar to an air traffic controller providing radarvectors, and just as with radar vectors, the guidanceis valid only for the intended aircraft. The TLSground equipment tracks one aircraft, based on itstransponder code, and provides correction signals tocourse and glidepath based on the position of thetracked aircraft. Flying the TLS corrections com-puted for another aircraft will not provide guidancerelative to the approach; therefore, aircrews must notuse the TLS signal for navigation unless they havereceived approach clearance and completed therequired coordination with the TLS ground equip-ment operator. Navigation fixes based onconventional NAVAIDs or GPS are provided in the

special instrument approach procedure to allowaircrews to verify the TLS guidance.

d. Special Category I Differential GPS (SCAT−I DGPS)

1. The SCAT−I DGPS is designed to provideapproach guidance by broadcasting differentialcorrection to GPS.

2. SCAT−I DGPS procedures require aircraftequipment and pilot training.

3. Ground equipment consists of GPS receiversand a VHF digital radio transmitter. The SCAT−IDGPS detects the position of GPS satellites relativeto GPS receiver equipment and broadcasts differen-tial corrections over the VHF digital radio.

4. Category I Ground Based AugmentationSystem (GBAS) will displace SCAT−I DGPS as thepublic use service.REFERENCE−AIM, Paragraph 5−4−7 f, Instrument Approach Procedures

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1−2−1Performance−Based Navigation (PBN) and Area Navigation (RNAV)

Section 2. Performance−Based Navigation (PBN) andArea Navigation (RNAV)

1−2−1. General

a. Introduction to PBN. As air travel hasevolved, methods of navigation have improved togive operators more flexibility. PBN exists under theumbrella of area navigation (RNAV). The termRNAV in this context, as in procedure titles, justmeans “area navigation,” regardless of the equipmentcapability of the aircraft. (See FIG 1−2−1.) Manyoperators have upgraded their systems to obtain thebenefits of PBN. Within PBN there are two maincategories of navigation methods or specifications:area navigation (RNAV) and required navigationperformance (RNP). In this context, the term RNAVx means a specific navigation specification with aspecified lateral accuracy value. For an aircraft tomeet the requirements of PBN, a specified RNAV orRNP accuracy must be met 95 percent of the flighttime. RNP is a PBN system that includes onboard

performance monitoring and alerting capability (forexample, Receiver Autonomous Integrity Monitor-ing (RAIM)). PBN also introduces the concept ofnavigation specifications (NavSpecs) which are a setof aircraft and aircrew requirements needed tosupport a navigation application within a definedairspace concept. For both RNP and RNAVNavSpecs, the numerical designation refers to thelateral navigation accuracy in nautical miles which isexpected to be achieved at least 95 percent of theflight time by the population of aircraft operatingwithin the airspace, route, or procedure. Thisinformation is detailed in International Civil AviationOrganization’s (ICAO) Doc 9613, Performance−based Navigation (PBN) Manual and the latest FAAAC 90−105, Approval Guidance for RNP Operationsand Barometric Vertical Navigation in the U.S.National Airspace System and in Remote andOceanic Airspace.

FIG 1−2−1

Navigation Specifications

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1−2−2 Performance−Based Navigation (PBN) and Area Navigation (RNAV)

b. Area Navigation (RNAV)

1. General. RNAV is a method of navigationthat permits aircraft operation on any desired flightpath within the coverage of ground− or space−basednavigation aids or within the limits of the capabilityof self−contained aids, or a combination of these. Inthe future, there will be an increased dependence onthe use of RNAV in lieu of routes defined byground−based navigation aids. RNAV routes andterminal procedures, including departure procedures(DPs) and standard terminal arrivals (STARs), aredesigned with RNAV systems in mind. There areseveral potential advantages of RNAV routes andprocedures:

(a) Time and fuel savings;

(b) Reduced dependence on radar vectoring,altitude, and speed assignments allowing a reductionin required ATC radio transmissions; and

(c) More efficient use of airspace.

In addition to information found in this manual,guidance for domestic RNAV DPs, STARs, androutes may also be found in AC 90−100, U.S.Terminal and En Route Area Navigation (RNAV)Operations.

2. RNAV Operations. RNAV procedures, suchas DPs and STARs, demand strict pilot awareness andmaintenance of the procedure centerline. Pilotsshould possess a working knowledge of their aircraftnavigation system to ensure RNAV procedures areflown in an appropriate manner. In addition, pilotsshould have an understanding of the variouswaypoint and leg types used in RNAV procedures;these are discussed in more detail below.

(a) Waypoints. A waypoint is a predeter-mined geographical position that is defined in termsof latitude/longitude coordinates. Waypoints may bea simple named point in space or associated withexisting navaids, intersections, or fixes. A waypointis most often used to indicate a change in direction,speed, or altitude along the desired path. RNAVprocedures make use of both fly−over and fly−bywaypoints.

(1) Fly−by waypoints. Fly−by waypointsare used when an aircraft should begin a turn to thenext course prior to reaching the waypoint separating

the two route segments. This is known as turnanticipation.

(2) Fly−over waypoints. Fly−over way-points are used when the aircraft must fly over thepoint prior to starting a turn.

NOTE−FIG 1−2−2 illustrates several differences between a fly−byand a fly−over waypoint.

FIG 1−2−2

Fly−by and Fly−over Waypoints

(b) RNAV Leg Types. A leg type describesthe desired path proceeding, following, or betweenwaypoints on an RNAV procedure. Leg types areidentified by a two−letter code that describes the path(e.g., heading, course, track, etc.) and the terminationpoint (e.g., the path terminates at an altitude, distance,fix, etc.). Leg types used for procedure design areincluded in the aircraft navigation database, but notnormally provided on the procedure chart. Thenarrative depiction of the RNAV chart describes howa procedure is flown. The “path and terminatorconcept” defines that every leg of a procedure has atermination point and some kind of path into thattermination point. Some of the available leg types aredescribed below.

(1) Track to Fix. A Track to Fix (TF) legis intercepted and acquired as the flight track to thefollowing waypoint. Track to a Fix legs aresometimes called point−to−point legs for this reason.Narrative: “direct ALPHA, then on course toBRAVO WP.” See FIG 1−2−3.

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(2) Direct to Fix. A Direct to Fix (DF) legis a path described by an aircraft’s track from an initialarea direct to the next waypoint. Narrative: “turnright direct BRAVO WP.” See FIG 1−2−4.

FIG 1−2−3

Track to Fix Leg Type

FIG 1−2−4

Direct to Fix Leg Type

(3) Course to Fix. A Course to Fix (CF)leg is a path that terminates at a fix with a specifiedcourse at that fix. Narrative: “on course 150 toALPHA WP.” See FIG 1−2−5.

FIG 1−2−5

Course to Fix Leg Type

(4) Radius to Fix. A Radius to Fix (RF)leg is defined as a constant radius circular path arounda defined turn center that terminates at a fix. SeeFIG 1−2−6.

FIG 1−2−6

Radius to Fix Leg Type

(5) Heading. A Heading leg may bedefined as, but not limited to, a Heading to Altitude(VA), Heading to DME range (VD), and Heading toManual Termination, i.e., Vector (VM). Narra-tive: “climb heading 350 to 1500”, “heading 265, at9 DME west of PXR VORTAC, right turn heading360”, “fly heading 090, expect radar vectors toDRYHT INT.”

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(c) Navigation Issues. Pilots should beaware of their navigation system inputs, alerts, andannunciations in order to make better−informeddecisions. In addition, the availability and suitabilityof particular sensors/systems should be considered.

(1) GPS/WAAS. Operators using TSO−C129(), TSO−C196(), TSO−C145() or TSO−C146()systems should ensure departure and arrival airportsare entered to ensure proper RAIM availability andCDI sensitivity.

(2) DME/DME. Operators should beaware that DME/DME position updating is depen-dent on navigation system logic and DME facilityproximity, availability, geometry, and signal mask-ing.

(3) VOR/DME. Unique VOR character-istics may result in less accurate values fromVOR/DME position updating than from GPS orDME/DME position updating.

(4) Inertial Navigation. Inertial referenceunits and inertial navigation systems are oftencoupled with other types of navigation inputs,e.g., DME/DME or GPS, to improve overallnavigation system performance.

NOTE−Specific inertial position updating requirements mayapply.

(d) Flight Management System(FMS). An FMS is an integrated suite of sensors,receivers, and computers, coupled with a navigationdatabase. These systems generally provide perfor-mance and RNAV guidance to displays and automaticflight control systems.

Inputs can be accepted from multiple sources such asGPS, DME, VOR, LOC and IRU. These inputs maybe applied to a navigation solution one at a time or incombination. Some FMSs provide for the detectionand isolation of faulty navigation information.

When appropriate navigation signals are available,FMSs will normally rely on GPS and/or DME/DME(that is, the use of distance information from two ormore DME stations) for position updates. Otherinputs may also be incorporated based on FMSsystem architecture and navigation source geometry.

NOTE−DME/DME inputs coupled with one or more IRU(s) areoften abbreviated as DME/DME/IRU or D/D/I.

(e) RNAV Navigation Specifications (NavSpecs)

Nav Specs are a set of aircraft and aircrewrequirements needed to support a navigationapplication within a defined airspace concept. Forboth RNP and RNAV designations, the numericaldesignation refers to the lateral navigation accuracyin nautical miles which is expected to be achieved atleast 95 percent of the flight time by the population ofaircraft operating within the airspace, route, orprocedure. (See FIG 1−2−1.)

(1) RNAV 1. Typically RNAV 1 is used forDPs and STARs and appears on the charts. Aircraftmust maintain a total system error of not more than1 NM for 95 percent of the total flight time.

(2) RNAV 2. Typically RNAV 2 is used foren route operations unless otherwise specified.T-routes and Q-routes are examples of this Nav Spec.Aircraft must maintain a total system error of notmore than 2 NM for 95 percent of the total flight time.

(3) RNAV 10. Typically RNAV 10 is usedin oceanic operations. See paragraph 4−7−1 forspecifics and explanation of the relationship betweenRNP 10 and RNAV 10 terminology.

1−2−2. Required Navigation Performance(RNP)

a. General. While both RNAV navigation speci-fications (NavSpecs) and RNP NavSpecs containspecific performance requirements, RNP is RNAVwith the added requirement for onboard performancemonitoring and alerting (OBPMA). RNP is also astatement of navigation performance necessary foroperation within a defined airspace. A criticalcomponent of RNP is the ability of the aircraftnavigation system to monitor its achieved navigationperformance, and to identify for the pilot whether theoperational requirement is, or is not, being met duringan operation. OBPMA capability therefore allows alessened reliance on air traffic control interventionand/or procedural separation to achieve the overallsafety of the operation. RNP capability of the aircraftis a major component in determining the separationcriteria to ensure that the overall containment of theoperation is met. The RNP capability of an aircraftwill vary depending upon the aircraft equipment andthe navigation infrastructure. For example, an aircraftmay be eligible for RNP 1, but may not be capable ofRNP 1 operations due to limited NAVAID coverage

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or avionics failure. The Aircraft Flight Manual(AFM) or avionics documents for your aircraftshould specifically state the aircraft’s RNP eligibili-ties. Contact the manufacturer of the avionics or theaircraft if this information is missing or incomplete.NavSpecs should be considered different from oneanother, not “better” or “worse” based on thedescribed lateral navigation accuracy. It is thisconcept that requires each NavSpec eligbility to belisted separately in the avionics documents or AFM.For example, RNP 1 is different from RNAV 1, andan RNP 1 eligibility does NOT mean automatic RNP2 or RNAV 1 eligibility. As a safeguard, the FAArequires that aircraft navigation databases hold onlythose procedures that the aircraft maintains eligibilityfor. If you look for a specific instrument procedure inyour aircraft’s navigation database and cannot find it,it’s likely that procedure contains PBN elements youraircraft is ineligible for or cannot compute and fly.Further, optional capabilities such as Radius−to−fix(RF) turns or scalability should be described in theAFM or avionics documents. Use the capabilities ofyour avionics suite to verify the appropriate waypointand track data after loading the procedure from yourdatabase.

b. PBN Operations.

1. Lateral Accuracy Values. Lateral Accuracyvalues are applicable to a selected airspace, route, orprocedure. The lateral accuracy value is a valuetypically expressed as a distance in nautical milesfrom the intended centerline of a procedure, route, orpath. RNP applications also account for potentialerrors at some multiple of lateral accuracy value (forexample, twice the RNP lateral accuracy values).

(a) RNP NavSpecs. U.S. standard NavSpecssupporting typical RNP airspace uses are as specifiedbelow. Other NavSpecs may include different lateralaccuracy values as identified by ICAO or other states.(See FIG 1−2−1.)

(1) RNP Approach (RNP APCH). In theU.S., RNP APCH procedures are titled RNAV (GPS)and offer several lines of minima to accommodatevarying levels of aircraft equipage: either lateralnavigation (LNAV), LNAV/vertical navigation(LNAV/VNAV), Localizer Performance with Verti-cal Guidance (LPV), and Localizer Performance(LP). GPS with or without Space−Based Augmenta-tion System (SBAS) (for example, WAAS) canprovide the lateral information to support LNAV

minima. LNAV/VNAV incorporates LNAV lateralwith vertical path guidance for systems and operatorscapable of either barometric or SBAS vertical. Pilotsare required to use SBAS to fly to the LPV or LPminima. RF turn capability is optional in RNP APCHeligibility. This means that your aircraft may beeligible for RNP APCH operations, but you may notfly an RF turn unless RF turns are also specificallylisted as a feature of your avionics suite. GBASLanding System (GLS) procedures are also con-structed using RNP APCH NavSpecs and provideprecision approach capability. RNP APCH has alateral accuracy value of 1 in the terminal and missedapproach segments and essentially scales to RNP 0.3(or 40 meters with SBAS) in the final approach. (SeeParagraph 5−4−18, RNP AR Instrument ApproachProcedures.)

(2) RNP Authorization Required Ap-proach (RNP AR APCH). In the U.S., RNP ARAPCH procedures are titled RNAV (RNP). Theseapproaches have stringent equipage and pilot trainingstandards and require special FAA authorization tofly. Scalability and RF turn capabilities aremandatory in RNP AR APCH eligibility. RNP ARAPCH vertical navigation performance is based uponbarometric VNAV or SBAS. RNP AR is intended toprovide specific benefits at specific locations. It is notintended for every operator or aircraft. RNP ARcapability requires specific aircraft performance,design, operational processes, training, and specificprocedure design criteria to achieve the requiredtarget level of safety. RNP AR APCH has lateralaccuracy values that can range below 1 in the terminaland missed approach segments and essentially scaleto RNP 0.3 or lower in the final approach. Beforeconducting these procedures, operators should referto the latest AC 90−101, Approval Guidance for RNPProcedures with AR. (See paragraph 5−4−18.)

(3) RNP Authorization Required Depar-ture (RNP AR DP). Similar to RNP AR approaches,RNP AR departure procedures have stringentequipage and pilot training standards and requirespecial FAA authorization to fly. Scalability and RFturn capabilities is mandatory in RNP AR DPeligibility. RNP AR DP is intended to providespecific benefits at specific locations. It is notintended for every operator or aircraft. RNP AR DPcapability requires specific aircraft performance,design, operational processes, training, and specificprocedure design criteria to achieve the required

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target level of safety. RNP AR DP has lateralaccuracy values that can scale to no lower than RNP0.3 in the initial departure flight path. Beforeconducting these procedures, operators should referto the latest AC 90−101, Approval Guidance for RNPProcedures with AR. (See paragraph 5−4−18.)

(4) Advanced RNP (A−RNP). AdvancedRNP is a NavSpec with a minimum set of mandatoryfunctions enabled in the aircraft’s avionics suite. Inthe U.S., these minimum functions include capabilityto calculate and perform RF turns, scalable RNP, andparallel offset flight path generation. Highercontinuity (such as dual systems) may be required forcertain oceanic and remote continental airspace.Other “advanced” options for use in the en routeenvironment (such as fixed radius transitions andTime of Arrival Control) are optional in the U.S.Typically, an aircraft eligible for A−RNP will also beeligible for operations comprising: RNP APCH,RNP/RNAV 1, RNP/RNAV 2, RNP 4, andRNP/RNAV 10. A−RNP allows for scalable RNPlateral navigation values (either 1.0 or 0.3) in theterminal environment. Use of these reduced lateralaccuracies will normally require use of the aircraft’sautopilot and/or flight director. See the latest AC90−105 for more information on A−RNP, includingNavSpec bundling options, eligibility determina-tions, and operations approvals.

NOTE−A−RNP eligible aircraft are NOT automatically eligible forRNP AR APCH or RNP AR DP operations, as RNP AReligibility requires a separate determination process andspecial FAA authorization.

(5) RNP 1. RNP 1 requires a lateralaccuracy value of 1 for arrival and departure in theterminal area, and the initial and intermediateapproach phase when used on conventional proce-dures with PBN segments (for example, an ILS witha PBN feeder, IAF, or missed approach). RF turncapability is optional in RNP 1 eligibility. This meansthat your aircraft may be eligible for RNP 1operations, but you may not fly an RF turn unless RFturns are also specifically listed as a feature of youravionics suite.

(6) RNP 2. RNP 2 will apply to bothdomestic and oceanic/remote operations with alateral accuracy value of 2.

(7) RNP 4. RNP 4 will apply to oceanic andremote operations only with a lateral accuracy value

of 4. RNP 4 eligibility will automatically conferRNP 10 eligibility.

(8) RNP 10. The RNP 10 NavSpec appliesto certain oceanic and remote operations with a lateralaccuracy of 10. In such airspace, the RNAV 10NavSpec will be applied, so any aircraft eligible forRNP 10 will be deemed eligible for RNAV 10operations. Further, any aircraft eligible for RNP 4operations is automatically qualified for RNP 10/RNAV 10 operations. (See also the latest AC 91−70,Oceanic and Remote Continental Airspace Opera-tions, for more information on oceanic RNP/RNAVoperations.)

(9) RNP 0.3. The RNP 0.3 NavSpecrequires a lateral accuracy value of 0.3 for allauthorized phases of flight. RNP 0.3 is not authorizedfor oceanic, remote, or the final approach segment.Use of RNP 0.3 by slow−flying fixed−wing aircraft isunder consideration, but the RNP 0.3 NavSpecinitially will apply only to rotorcraft operations. RFturn capability is optional in RNP 0.3 eligibility. Thismeans that your aircraft may be eligible for RNP 0.3operations, but you may not fly an RF turn unless RFturns are also specifically listed as a feature of youravionics suite.

NOTE−On terminal procedures or en route charts, do not confusea charted RNP value of 0.30, or any standard finalapproach course segment width of 0.30, with the NavSpectitle “RNP 0.3.” Charted RNP values of 0.30 or belowshould contain two decimal places (for example, RNP 0.15,or 0.10, or 0.30) whereas the NavSpec title will only state“RNP 0.3.”

(b) Application of Standard Lateral Accu-racy Values. U.S. standard lateral accuracy valuestypically used for various routes and proceduressupporting RNAV operations may be based on use ofa specific navigational system or sensor such as GPS,or on multi−sensor RNAV systems having suitableperformance.

(c) Depiction of PBN Requirements. In theU.S., PBN requirements like Lateral AccuracyValues or NavSpecs applicable to a procedure will bedepicted on affected charts and procedures. In theU.S., a specific procedure’s Performance−BasedNavigation (PBN) requirements will be prominentlydisplayed in separate, standardized notes boxes. Forprocedures with PBN elements, the “PBN box” willcontain the procedure’s NavSpec(s); and, if required:specific sensors or infrastructure needed for the

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navigation solution, any additional or advancedfunctional requirements, the minimum RNP value,and any amplifying remarks. Items listed in this PBNbox are REQUIRED to fly the procedure’s PBNelements. For example, an ILS with an RNAV missedapproach would require a specific capability to fly themissed approach portion of the procedure. Thatrequired capability will be listed in the PBN box. Theseparate Equipment Requirements box will listground−based equipment and/or airport specificrequirements. On procedures with both PBNelements and ground−based equipment require-ments, the PBN requirements box will be listed first.(See FIG 5−4−1.)

c. Other RNP Applications Outside the U.S.The FAA and ICAO member states have ledinitiatives in implementing the RNP concept tooceanic operations. For example, RNP−10 routes

have been established in the northern Pacific(NOPAC) which has increased capacity andefficiency by reducing the distance between tracksto 50 NM. (See paragraph 4−7−1.)

d. Aircraft and Airborne Equipment Eligibilityfor RNP Operations. Aircraft eligible for RNPoperations will have an appropriate entry includingspecial conditions and limitations in its AFM,avionics manual, or a supplement. Operators ofaircraft not having specific RNP eligibility state-ments in the AFM or avionics documents may beissued operational approval including special condi-tions and limitations for specific RNP eligibilities.

NOTE−Some airborne systems use Estimated Position Uncertain-ty (EPU) as a measure of the current estimatednavigational performance. EPU may also be referred to asActual Navigation Performance (ANP) or EstimatedPosition Error (EPE).

TBL 1−2−1

U.S. Standard RNP Levels

RNP Level Typical Application Primary RouteWidth (NM) −Centerline to

Boundary

0.1 to 1.0 RNP AR Approach Segments 0.1 to 1.0

0.3 to 1.0 RNP Approach Segments 0.3 to 1.0

1 Terminal and En Route 1.0

2 En Route 2.0

4 Projected for oceanic/remote areas where 30 NM horizontalseparation is applied.

4.0

10 Oceanic/remote areas where 50 NM lateral separation isapplied.

10.0

1−2−3. Use of Suitable Area Navigation(RNAV) Systems on ConventionalProcedures and Routes

a. Discussion. This paragraph sets forth policy,while providing operational and airworthinessguidance regarding the suitability and use of RNAVsystems when operating on, or transitioning to,conventional, non−RNAV routes and procedureswithin the U.S. National Airspace System (NAS):

1. Use of a suitable RNAV system as aSubstitute Means of Navigation when a Very−HighFrequency (VHF) Omni−directional Range (VOR),

Distance Measuring Equipment (DME), Tactical AirNavigation (TACAN), VOR/TACAN (VORTAC),VOR/DME, Non−directional Beacon (NDB), orcompass locator facility including locator outermarker and locator middle marker is out−of−service(that is, the navigation aid (NAVAID) information isnot available); an aircraft is not equipped with anAutomatic Direction Finder (ADF) or DME; or theinstalled ADF or DME on an aircraft is notoperational. For example, if equipped with a suitableRNAV system, a pilot may hold over an out−of−ser-vice NDB.

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2. Use of a suitable RNAV system as anAlternate Means of Navigation when a VOR, DME,VORTAC, VOR/DME, TACAN, NDB, or compasslocator facility including locator outer marker andlocator middle marker is operational and therespective aircraft is equipped with operationalnavigation equipment that is compatible withconventional navaids. For example, if equipped witha suitable RNAV system, a pilot may fly a procedureor route based on operational VOR using that RNAVsystem without monitoring the VOR.

NOTE−1. Additional information and associated requirementsare available in Advisory Circular 90-108 titled “Use ofSuitable RNAV Systems on Conventional Routes andProcedures.”

2. Good planning and knowledge of your RNAV system arecritical for safe and successful operations.

3. Pilots planning to use their RNAV system as a substitutemeans of navigation guidance in lieu of an out−of−serviceNAVAID may need to advise ATC of this intent andcapability.

4. The navigation database should be current for theduration of the flight. If the AIRAC cycle will changeduring flight, operators and pilots should establishprocedures to ensure the accuracy of navigation data,including suitability of navigation facilities used to definethe routes and procedures for flight. To facilitate validatingdatabase currency, the FAA has developed procedures forpublishing the amendment date that instrument approachprocedures were last revised. The amendment date followsthe amendment number, e.g., Amdt 4 14Jan10. Currency ofgraphic departure procedures and STARs may beascertained by the numerical designation in the proceduretitle. If an amended chart is published for the procedure, orthe procedure amendment date shown on the chart is on orafter the expiration date of the database, the operator mustnot use the database to conduct the operation.

b. Types of RNAV Systems that Qualify as aSuitable RNAV System. When installed in accor-dance with appropriate airworthiness installationrequirements and operated in accordance withapplicable operational guidance (for example,aircraft flight manual and Advisory Circularmaterial), the following systems qualify as a suitableRNAV system:

1. An RNAV system with TSO−C129/−C145/−C146 equipment, installed in accordancewith AC 20−138, Airworthiness Approval of GlobalPositioning System (GPS) Navigation Equipment for

Use as a VFR and IFR Supplemental NavigationSystem, and authorized for instrument flight rules(IFR) en route and terminal operations (includingthose systems previously qualified for “GPS in lieu ofADF or DME” operations), or

2. An RNAV system with DME/DME/IRUinputs that is compliant with the equipmentprovisions of AC 90−100A, U.S. Terminal andEn Route Area Navigation (RNAV) Operations, forRNAV routes. A table of compliant equipment isavailable at the following website:https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afx/afs/afs400/afs410/media/AC90−100compliance.pdf

NOTE−Approved RNAV systems using DME/DME/IRU, withoutGPS/WAAS position input, may only be used as a substitutemeans of navigation when specifically authorized by aNotice to Airmen (NOTAM) or other FAA guidance for aspecific procedure. The NOTAM or other FAA guidanceauthorizing the use of DME/DME/IRU systems will alsoidentify any required DME facilities based on an FAAassessment of the DME navigation infrastructure.

c. Uses of Suitable RNAV Systems. Subject tothe operating requirements, operators may use asuitable RNAV system in the following ways.

1. Determine aircraft position relative to, ordistance from a VOR (see NOTE 6 below), TACAN,NDB, compass locator, DME fix; or a named fixdefined by a VOR radial, TACAN course, NDBbearing, or compass locator bearing intersecting aVOR or localizer course.

2. Navigate to or from a VOR, TACAN, NDB,or compass locator.

3. Hold over a VOR, TACAN, NDB, compasslocator, or DME fix.

4. Fly an arc based upon DME.

NOTE−1. The allowances described in this section apply evenwhen a facility is identified as required on a procedure (forexample, “Note ADF required”).

2. These operations do not include lateral navigation onlocalizer−based courses (including localizer back−courseguidance) without reference to raw localizer data.

3. Unless otherwise specified, a suitable RNAV systemcannot be used for navigation on procedures that areidentified as not authorized (“NA”) without exception bya NOTAM. For example, an operator may not use a RNAVsystem to navigate on a procedure affected by an expired or

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unsatisfactory flight inspection, or a procedure that isbased upon a recently decommissioned NAVAID.

4. Pilots may not substitute for the NAVAID (for example,a VOR or NDB) providing lateral guidance for the finalapproach segment. This restriction does not refer toinstrument approach procedures with “or GPS” in the titlewhen using GPS or WAAS. These allowances do not applyto procedures that are identified as not authorized (NA)without exception by a NOTAM, as other conditions maystill exist and result in a procedure not being available. Forexample, these allowances do not apply to a procedureassociated with an expired or unsatisfactory flightinspection, or is based upon a recently decommissionedNAVAID.

5. Use of a suitable RNAV system as a means to navigateon the final approach segment of an instrument approachprocedure based on a VOR, TACAN or NDB signal, isallowable. The underlying NAVAID must be operationaland the NAVAID monitored for final segment coursealignment.

6. For the purpose of paragraph c, “VOR” includes VOR,VOR/DME, and VORTAC facilities and “compasslocator” includes locator outer marker and locator middlemarker.

d. Alternate Airport Considerations. For thepurposes of flight planning, any required alternateairport must have an available instrument approachprocedure that does not require the use of GPS. Thisrestriction includes conducting a conventionalapproach at the alternate airport using a substitutemeans of navigation that is based upon the use ofGPS. For example, these restrictions would applywhen planning to use GPS equipment as a substitutemeans of navigation for an out−of−service VOR thatsupports an ILS missed approach procedure at analternate airport. In this case, some other approachnot reliant upon the use of GPS must be available.This restriction does not apply to RNAV systemsusing TSO−C145/−C146 WAAS equipment. Forfurther WAAS guidance, see paragraph 1−1−18.

1. For flight planning purposes, TSO-C129()and TSO-C196() equipped users (GPS users) whosenavigation systems have fault detection andexclusion (FDE) capability, who perform a preflightRAIM prediction at the airport where the RNAV(GPS) approach will be flown, and have properknowledge and any required training and/or approvalto conduct a GPS-based IAP, may file based on aGPS-based IAP at either the destination or thealternate airport, but not at both locations. At the

alternate airport, pilots may plan for applicablealternate airport weather minimums using:

(a) Lateral navigation (LNAV) or circlingminimum descent altitude (MDA);

(b) LNAV/vertical navigation (LNAV/VNAV) DA, if equipped with and using approvedbarometric vertical navigation (baro-VNAV) equip-ment;

(c) RNP 0.3 DA on an RNAV (RNP) IAP, ifthey are specifically authorized users using approvedbaro-VNAV equipment and the pilot has verifiedrequired navigation performance (RNP) availabilitythrough an approved prediction program.

2. If the above conditions cannot be met, anyrequired alternate airport must have an approvedinstrument approach procedure other than GPS that isanticipated to be operational and available at theestimated time of arrival, and which the aircraft isequipped to fly.

3. This restriction does not apply toTSO-C145() and TSO-C146() equipped users(WAAS users). For further WAAS guidance, seeparagraph 1−1−18.

1−2−4. Pilots and Air Traffic ControllersRecognizing Interference or Spoofing

a. Pilots need to maintain position awarenesswhile navigating. This awareness may be facilitatedby keeping relevant ground−based, legacy naviga-tional aids tuned and available. By utilizing thispractice, situational awareness is promoted andguards against significant pilot delay in recognizingthe onset of GPS interference. Pilots may findcross−checks of other airborne systems (for example,DME/DME/IRU or VOR) useful to mitigate thisotherwise undetected hazard.REFERENCE−AIM Paragraph 1−1−17, Global Positioning System (GPS)AIM Paragraph 1−1−18, Wide Area Augmentation System (WAAS)

b. During preflight planning, pilots should beparticularly alert for NOTAMs which could affectnavigation (GPS or WAAS) along their route offlight, such as Department of Defense electronicsignal tests with GPS.REFERENCE−AIM Paragraph 1−1−17, Global Positioning System (GPS)AIM Paragraph 1−1−18, Wide Area Augmentation System (WAAS)

c. If the pilot experiences interruptions whilenavigating with GPS, the pilot and ATC may both

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incur a higher workload. In the aircraft, the pilot mayneed to change to a position determining method thatdoes not require GPS−derived signals (for example,DME/DME/IRU or VOR). If transitioning to VORnavigation, the pilot should refer to the current ChartSupplement U.S. to identify airports with availableconventional approaches associated with the VORMinimum Operational Network (MON) program. Ifthe pilot’s aircraft is under ATC radar or multilatera-tion surveillance, ATC may be able to provide radarvectors out of the interference affected area or to analternate destination upon pilot request. An ADS−BOut aircraft’s broadcast information may be incorrectand should not be relied upon for surveillance wheninterference or spoofing is suspected unless itsaccuracy can be verified by independent means.During the approach phase, a pilot might elect tocontinue in visual conditions or may need to execute

the published missed approach. If the publishedmissed approach procedure is GPS−based, the pilotwill need alternate instructions. If the pilot were tochoose to continue in visual conditions, the pilotcould aid the controller by cancelling his/her IFRflight plan and proceeding visually to the airport toland. ATC would cancel the pilot’s IFR clearance andissue a VFR squawk; freeing up the controller tohandle other aircraft.

d. The FAA requests that pilots notify ATC if theyexperience interruptions to their GPS navigation orsurveillance. GPS interference or outages associatedwith a known testing NOTAM should not be reportedto ATC unless the interference/outage affects thepilot’s ability to navigate his/her aircraft.REFERENCE−AIM Paragraph 1−1−13, User Reports Requested on NAVAID or GlobalNavigation Satellite System (GNSS) Performance or Interference.

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