Mission Aircrew Course Chapter 10: Electronic Search Patterns (Mar 2007)

Mission Aircrew Mission Aircrew CourseCourse

Chapter 10: Electronic Chapter 10: Electronic Search PatternsSearch Patterns

(Mar 2007)(Mar 2007)

O-2005 OPERATE THE AIRCRAFT DIRECTION FINDER (P)

O-2006 PERFORM ELT SEARCHES (P) O-2007 LOCATE AND SILENCE AN ELT ON

THE GROUND (P) O-2101 DESCRIBE HOW ELTS ARE

DETECTED (P) O-2108 ASSIST IN ELT SEARCHES (O)

Aircrew TasksAircrew Tasks

Discuss the various types of ELTs. {O; 10.1.1}

Describe how an ELT can be detected. {O; 10.2}

Describe how the aircraft DF works in both the Alarm and DF modes. {O; 10.3.1}

Discuss using the DF during a typical ELT search {O; 10.3.2}

• Response during initial phase, including signal fade• Response when getting close• Response as you pass over the beacon

ObjectivesObjectives

Describe the following ELT search methods: {O; 10.4 – 10.7}

• Homing• Wing null• Aural• Signal

Discuss signal reflection and interference. {O; 10.9}

Describe how to silence an ELT and the legal issues involved. {O; 10.10}

ObjectivesObjectives

©2000 Scott E. Lanis 5

Emergency Locator Emergency Locator TransmitterTransmitter

Direction Finding for Direction Finding for Aircrews:Aircrews:

use of equipment commonly use of equipment commonly found in CAP aircraftfound in CAP aircraft

N98987N98987


Objective: The Objective: The Elusive ELTElusive ELT

Automatic radio beacon (100 milliwatts)• Roughly equal to that of a regular flashlight

Can be heard on a line-of-sight basis. Remember that the ELT may be attached

to an aircraft or vessel in distress!

Wave Sound

Click Icon to Hear an ELT

Activated by g-force (when armed)• Some can be activated by the pilot in the cockpit

Three frequencies:• 121.5 MHz (VHF emergency)• 243 MHz (UHF emergency – military guard)• 406.025 MHz (third generation advanced

ELT/EPIRB/PLB)

General types:• General aviation aircraft• Military (“beepers” or “beacons”)• Marine EPIRB• Test station (training practice beacon)• Personal Locator Beacons (PLBs)• Advanced (406)

The The ELTELT

ELT ELT AntennaAntenna

Most aircraft have ELTs Most aircraft have ELTs installedinstalled

But they But they don’t don’t

always always survive a survive a

crashcrash

Most common type is the URT-33/C Personnel ejecting/parachuting will have

a 243 MHz beacon Some downed pilots may be able to

communicate via two-way radio on 243 MHz using a PRC-90 military survival radio

• Beacon mode transmits like an ELT on 243 MHz• You can monitor this frequency on your aircraft DF

Military Military beaconsbeacons

Personal Locator Beacon (PLB) or Personal Emergency Transmitter (PET):

• Intended for hikers and other remote wilderness travelers

• MOST Use a 406 MHz transmitter and a 121.5 MHz homing signal (at only 25 milliwatts)

• Many are also equipped with a built-in GPS receiver that provides lat/long coordinates

• Each PLB must be registered• See discussion of Advanced ELTs

Personal Personal beaconsbeacons

http://www.micro-mono.com/microplb/microplb.html

Emergency Position Indicating Radio Beacon

Similar to an ELT, an EPIRB is used on ships and boats

Mandatory on certain commercial vessels Some activate automatically and others are

manually activated Many are now 406 capable

Marine Marine EPIRBEPIRB

Designed to operate with SARSAT/COSPAS• 406.025 MHz beacons have data burst encoding that

identifies each (registered) individual beacon• Also produces a 121.5 MHz homing signal and may

transmit GPS coordinates• Sends a coded signal that can be used to obtain the

owner's name, address and type of aircraft, so AFRCC can call the number to see if the aircraft is really missing (70% resolved)

• Since geostationary satellites process the signal it will be heard more quickly and allow a much faster response (~ 6 hours). If the unit has a GPS receiver, it can transmit lat/long coordinates to further speed the search. The signal can also penetrate dense cover (e.g., trees).

• Still very expensive (~ three times as much as a 121.5 MHz ELT)

Advanced Advanced ELTsELTs

Training Practice Beacons• Includes ones used by CAP

All should be converted from 121.6 to 121.775 MHz by now (if it isn’t, don’t use it, get it fixed)

During practice searches, avoid calling the practice beacon an ‘ELT’ when communicating over the radio

• May cause confusion

Always use the term ‘Practice Beacon’

Practice Practice BeaconBeacon

Can test the aircraft’s ELT within the first five minutes after each hour

Only allowed up to three sweeps When was the last time you tested the

ELT in your aircraft? Do you regularly monitor 121.5 MHz after

you land?• Ensure your ELT didn’t activate• This isn’t considered a test, by the way, but you can

try this excuse if you like

Testing an Testing an Aircraft ELTAircraft ELT

Excessively hard landings (Welcome aboard, Ensign!)

Inadvertent change of switch position During removal/installation Malfunction Non-ELT source on 121.5 MHz (computers,

broadcast stations, even pizza ovens!) Monsieur Murphy

Inadvertent Inadvertent ActivationActivation

At least 97%+ of received ELT signals are false alarms

• For 121.5 MHz ELTs abut 1 in 1000 are actual emergencies(2 in 100 composite alerts)

• For 406 MHz ELTs abut 1 in 10 are actual emergencies

What’s the big deal?• SARSAT can only monitor 10 ELTs at once• Easy to overload the system• They block emergency communications on 121.5 and

243 MHz (guarded by towers, ARTCC, and the military)

False False AlarmsAlarms

Detection Detection TimelineTimeline

For a regular 121.5 MHz beacon:• Said to be a 12-16 nautical mile radius (~ 452 square

nm)• Actually an oval shape with a 50% probability of

being 15 nm wide and 7 nm high• System is more accurate North to South (latitude)• Average six-hour detection/alert

For a 406 MHz beacon it’s a 1-3 nm radius (~ 12.4 square nm) with 45 – 60 minute detection/alert

For a 406 MHz beacon with GPS it’s a 0.05 nm radius (within 100 yards) with an average five-minute detection/alert

Accuracy of Accuracy of SARSAT/COSPSARSAT/COSP

ASAS

SARSAT VideoSARSAT Video

QUESTIONSQUESTIONS??

AS AN EMERGENCY! Its not possible to know whether an ELT

signal is a distress signal or a false alarm Although the statistics are against it, you

must act as though it is a distress call If you take advantage of it, every ELT

mission allows you to keep your skills sharp!

OK, So How Should I OK, So How Should I Treat an ELT Mission?Treat an ELT Mission?

Route or parallel track to pick up the signal

If no SARSAT hits or definitive LKP:• 4,000 to 10,000 AGL• Large track spacing (start at 60 nm, then do halves)

Once signal is located, DF the signal

Locating the ELT Locating the ELT SignalSignal

Direction Finder Direction Finder (DF)(DF)

•A direction finder compares signal strengths from two antenna patterns to let the user know:

– When you are “centered” on a signal•headed directly towards OR away from from the signal source

– Which direction to turn when not centered

– Similar to an ADF needle, but only points left or right, hence the term “left-right homing”

L-Tronics L-Tronics DFDF

Normal: Alarm toggle in ‘up’ position DF: toggle is ‘down’

DF DF AntennaAntenna

These are mounted on the bottom, but may be on top


Step 1: Acquire the Step 1: Acquire the SignalSignal

To hear the signal you can use your L-Tronics receiver or one of your comm radios

To acquire with a comm radio, turn the squelch OFF (pull out the volume knob out or flip the appropriate switch)

• The static you hear may be annoying, but it will allow you to hear the signal at the earliest possible time

• Allows for a weak or distant signal to be heard

Proceed at a reasonable altitude to the SARSAT composite hit, or to the point designated by your incident commander


NO SIGNAL

SIGNALSIGNALHEARD!HEARD!

NO SIGNALELT

Beginning The Search: Beginning The Search: Altitude SelectionAltitude Selection

Higher altitudes allow for reception of the ELT signal at greater distances

ELTs transmit on 121.5 MHz and 243.0 MHz, both of which limit reception to “line of sight”

Terrain will block ELT signals HIGHER is therefore usually BETTER to acquire a

signal Medium altitude is generally better for searching

(after signal heard)• 3,000 to 5,000 AGL

31©2000 Scott E. Lanis

ELT RECEPTION DISTANCE

0

5000

10000

15000

20000

25000

30000

35000

40000

0 18 30 34 56 69 95 121

147

200

265

DISTANCE, Nautical Miles

ALT

ITU

DE

, Fe

et

AG

L

Altitude Altitude SelectionSelection


Step 2: Track (DF) the Step 2: Track (DF) the SignalSignal

There are many different ways to DF an ELT signal:

• Left-Right DF Homing (L-Tronics DF)• Wing Shadow Method• Aural Search• Metered Search• Combinations of the above techniques


Wing Wing ShadowingShadowing

By flying the airplane in a circle, at some point the wing will block the ELT signal to the receiver antenna

• This causes an audible decrease in volume, called a “null”

Almost any VHF-AM aircraft communications radio may be used with this method


Wing Shadowing: Wing Shadowing: AntennasAntennas

To properly use the Wing Shadowing method, you MUST know where the antenna for the radio you are using is installed & located on the aircraft

Communications radio antennas are usually, but not always, located above the wings

• Can be above the fuselage, in the tail, etc. L-Tronics Aircraft DF antennas may be

above or below the aircraft• Below the aircraft is the preferred installation


Communications Communications Antennas Antennas

Above the WingAbove the Wing

N98987N98987

Antennas Abovethe Wing


DF Antennas Below the DF Antennas Below the WingWing

N98987N98987

Antennas Belowthe Wing

QUESTIONS?


How To DF by Wing How To DF by Wing ShadowingShadowing

(Also Called Wing-Null (Also Called Wing-Null Method)Method)

Fly a constant bank angle 360° turn

the audio will “null,” or get significantly

quieter, when your wing blocks the

antenna’s reception of the ELT signal

N

SE

W

45

135

225

315


Wing Shadowing:Wing Shadowing:Signal BlockingSignal Blocking

For Antennas Above the For Antennas Above the WingsWings

SIGNAL

ELT

NULL

NULL

NULL


Wing Shadowing:Wing Shadowing:Antennas Above the Antennas Above the

WingWing

Turn in a circle until you hear the null (significant decrease in volume)

The ELT is 90º to your LEFT SUBTRACT 90º from your

heading Or, keep it simple—use the

90º index

N

S

E

W

45135

225

315

ELT


Wing Shadowing: Wing Shadowing: Signal BlockingSignal Blocking

For Antennas Below the For Antennas Below the WingsWings

SIGNAL

ELT

NULL

NULL

NULL


Wing Wing Shadowing:Shadowing:

Antennas Below the Antennas Below the WingWing

Turn in a circle until you hear the null (significant decrease in volume)

The ELT is 90º to your RIGHT: ADD 90º to your heading

N

S

E

W

45

135

225

315

ELT


Aural (Hearing) Search Aural (Hearing) Search MethodMethod

This is based on the assumption that the area of equal beacon signal strength is circular: do NOT adjust volume during this search; you will need it to determine equal levels of signal

Begin by plotting your position as soon as you receive the ELT signal

Fly that course for a short distance, then turn 90º left or right and proceed until the signal fades

Turn around (180º) and mark where the signal fades on the other side of the circle

Plot chord lines similar to that of the diagram Bisect the chord lines at a perpendicular Plot a course to the location where the perpendicular

lines intersect: this should be the location of the target!


Aural SearchAural SearchEqual signal strength circle:barely audible signal in aircraftreceiver at search altitude

chord 1

chord 2

chord

3

ELTcommence low altitude patterndescending

SIGNALFADES

SIGNALHEARD

SIGNALHEARD

SIGNALHEARD

SIGNALFADES


Metered SearchMetered Search(Build & Fade) (Build & Fade)

MethodMethod

This search requires a signal strength meter (like that on the L-Tronics DF units-if the DF portion of the unit is inoperative you can still use this type of search as long as RECeive is OK.

Note your signal strength when beginning the search.

Fly a straight line until the signal gets lower, then increases to your original level.

Turn 180º and return to the lowest level of signal, then turn 90º left or right.

You should now be headed directly towards or away from the transmitter.

If the signal increases in strength, you are headed directly for the ELT.

If the signal decreases in strength, turn 180º


Metered SearchMetered Search

FADE

MAXIMUM

SIGNAL

MAXIMUM SIGNALTHEN DROP

FIRST SIGNAL1

2

3

4

5

6

ELT

2

2

2

4

4

4

6

6

7

8

7

8

95

5


Left-Right DF Left-Right DF HomingHoming

Most CAP corporate aircraft have L-Tronics LA-Series Left-Right Homing DF units

These units operate virtually the same, but there are two major varieties:

• Single Meter Models• Dual Meter Models


L-Tronics DF L-Tronics DF TypesTypes

Single Meter Model

Dual Meter Model

L-Tronics

ALARM

OFF

243

121.6

121.775 AUX

121.5

SENS VOL

VHFDF

DF STRENGTH

L-Tronics

ALARM

OFF

SENS VOL

VHF-DF

243

121.6

121.775 AUX

121.5

DF

REC


Frequency Frequency SwitchSwitch

Selects frequency to be used Use 121.5 MHz for actual ELTs/EPIRBs 243.0 MHz may also be used for all actual

electronic searches Use 121.775 MHz for training Refer to owners manual for use of the “AUX”

position

L-Tronics

ALARM

OFF

SENS VOL

VHF-DF

243

121.6

121.775 AUX

121.5

DF

REC


Mode Mode SwitchSwitch

Only Single-meter units have this switch• Dual-meter units use two displays, so both REC and DF operate

continuously and simultaneously REC is short for RECeive mode

• REC makes the unit’s dial work as a strength meter DF is short for Direction Find

• DF gives left-right homing to the ELT/EPIRB signal ALARM is for NON-MISSION flights only

• Use only during normal flying to alert the presence of an ELT or EPIRB

L-Tronics

ALARM

OFF

SENS VOL

VHF-DF

243

121.6

121.775 AUX

121.5

DF

REC


Volume & Volume & SensitivitySensitivity

Volume controls the audio level to the speaker or headsets Sensitivity controls the amount of signal that enters into the

DF unit• It is critical that the proper amount of signal enters the

DF: half-scale, or the middle, is an optimum starting place As the signal gets stronger, reduce SENSITIVITY, not volume

• The DF will be unreliable when too much signal is received, so you must cut out part of it by reducing the sensitivity

• More than three-quarters scale is too much

L-Tronics

ALARM

OFF

243

121.6

121.775 AUX

121.5

SENS VOL

VHFDF

DF STRENGTH


DF SETTINGS FOR DF SETTINGS FOR SINGLE METER SINGLE METER

MODELSMODELS

MISSIONS• Select 121.5 (or 121.775 for training missions)• Select DF Mode• Turn Sensitivity to Maximum (Full Clockwise)• Turn Volume to About Mid-Scale (comfortable level)• DF Needle Will Move Slightly Left and Right

NON-MISSION FLIGHTS• Select 121.5• Select Alarm Mode• Turn Sensitivity To Maximum• Do not fly a mission in the alarm mode, it takes too

long to activate


DF SETTINGS FORDF SETTINGS FORDUAL METER DUAL METER

MODELSMODELS

MISSIONS• Select 121.5 (or 121.775 for training missions)

• Ensure Alarm Toggle OFF• Turn Sensitivity to Maximum (Full Clockwise)• Turn Volume to About Mid-Scale (comfortable

level)• DF Should Stay About Centered• Strength Meter Will Move Up-Scale to Right

NON-MISSION FLIGHTS• Select 121.5• Turn Alarm Toggle On• Turn Sensitivity To Maximum


PRE-FLIGHT PRE-FLIGHT FUNCTIONAL CHECKFUNCTIONAL CHECK

Just as you pre-flight the rest of the aircraft, you should preflight your DF when going on an ELT electronic search mission

These procedures are covered in the Mission Aircrew Reference Text and are summarized for premission reference in the Flight Guide.


SIX SIX STEPSSTEPS

Use these 6 steps for locating ELTs and EPIRBs with L-Tronics LA- series airborne DF equipment

Use the full procedure every time for the best results

• RECeive• HALF• DF• TURN• CHECK• SHOOT

Each of these steps will be described in detail in the slides to follow


Step 1: Step 1: RECeiveRECeive

Once you have started to receive the ELT or EPIRB signal on the proper frequency

If you have a single-meter unit, turn the mode selector to RECeive and turn the volume to a comfortable level

If you have a dual meter unit, refer to the STRENGTH window (no need to change modes)

RECeive RECeive Mode/STRENGTH Mode/STRENGTH

WindowWindow

In receive mode or in the strength window, the unit measures signal strength

• Needle to the left means low; to the right means high

Values are relative depending on the sensitivity you have selected

You may still be able to use the strength meter even if the DF is not functioning perfectly

• It is possible to locate an ELT using only the Receive Mode• Utilize Aural Search/Metered Search methods to accomplish• If the unit isn’t completely operable, try wing shadowing using

one of the aircraft’s communications radios and use the DF unit’s strength meter as a backup using the aural/metered methods


Step 2: Step 2: HALFHALF

Now that the unit is in RECeive mode and you have a good signal, turn the Sensitivity Knob to HALF SCALE

• This is in the center of the window

If you are flying with a dual-meter unit, turn the Sensitivity Knob so the needle reads HALF SCALE in the STRENGTH window

A half-scale strength reading will prevent too much signal (over sense) from entering the unit and will provide you with a good starting point

It is also the optimum for the DF homing antennas


Step 3: Step 3: DFDF

For single-meter units, turn the mode selector knob to DF

In DF mode, you can think of the needle as always pointing Direct to Follow the target.

For dual-meter models, simply refer to the DF window (no need to change modes)

A Direction Finding Primer:A Direction Finding Primer:Antenna TheoryAntenna Theory

Antennas can be more or less directional depending on their design

Imagine a car radio antenna: it is unidirectional• Its pattern looks like the one on the left

A Satellite Dish is highly directional• It would have a pattern like the one on the

right

car radio antenna(monopole)

satellite dish (parabolic reflector)

DF DF AntennaAntenna

The aircraft DF unit has a 2 or 3 “element” antenna

• Commonly, we might call this two or three antennas• It just means there are two or three rods!

This antenna setup is directional• One element actually receives the signal• The other elements (rods) reflect the signal away

from the first rod

Antenna Elements

N98987N98987

Antennas Belowthe Wing


Antenna Reception Antenna Reception PatternPattern

When viewed from the bottom, an antenna setup like the one pictured on the previous slide produces a reception pattern like the one shown here

• This pattern is called “carotid,” which means “heart-shaped”

The pattern is the same even if the antennas are mounted above the wing

Element 1 2 3

DF Unit Antenna PatternDF Unit Antenna Pattern

AIRCRAFT VIEW

TOP VIEW

RECEIVINGELEMENT

REFLECTORELEMENTS

DIRECTIONALANTENNAPATTERN

Direction Direction Finding Finding

Mode/WindowMode/Window

The DF mode rapidly alternates the receiving and reflecting antenna elements

• It chooses one element as the receiver and the other two as the reflectors, then switches to the other set

This produces a carotid pattern each time the unit switches

• one is shown in blue, the other in yellow

By comparing the two patterns, the unit will determine when they are equal

When they’re equal, the needle centers! When the needle is centered,

the target is either directly ahead or behind you!


Step 4: Step 4: TURNTURN

Turn at least one FULL circle, noting where the DF needle centers

Under good conditions, the needle will center twice

• When facing directly at the source of the signal• When facing 180º away from the target

You will solve this problem (called ambiguity) in the next step

DF DF CENTERSCENTERS

AlternatingAntennaPatterns

AlternatingAntennaPatterns

WHEN THE PATTERNS

ARE EQUAL, THE DF NEEDLE

CENTERS!

ELT (Possibility 1)

ELT (Possibility 2)


Step 5: Step 5: CHECKCHECK

Use a Turn to Tell Remembering that in DF mode the

needle always points Direct to Follow the target

When you have the needle centered, turn left or right

• If you turn left and the needle goes left, the ELT is 180º from your present heading

• If you turn left and the needle turns right, the ELT is dead ahead

AMBIGUITAMBIGUITYY

ELT (Possibility 1)

ELT (Possibility 2)

When Needle Centers

• ELT is Directly Ahead or Behind

This situation is called “ambiguity”

To Solve ambiguity:

Use Turn to Tell• Make a turn left or

right• The needle always

pointsDirect to Follow the Target (DF!)

DF DF NEEDLENEEDLE

ELT

Compare the RED (LEFT) and the BLACK (RIGHT) antenna patterns

In this case, the LEFT pattern is stronger than the RIGHT

In DF mode, the needle would thenpoint LEFT

The needle always points Direct to Follow the Target!

SOLVING SOLVING AMBIGUITAMBIGUIT

YY

Actual ELT positionis unknown to user

Make a small turn left or right

• As a teachingreminder, “Use aTURN to TELL”

ELT (Possibility 1)

ELT (Possibility 2)

SOLVING SOLVING AMBIGUITYAMBIGUITY




Example:• TURN LEFT• needle goes left

ELT (Possibility 1)

ELT (Possibility 2)


YY




Example:• TURN LEFT• If needle goes left• ELT is to your left

(behind you)

ELT (Possibility 2)


YY

If you turn Left and theneedle moves Right

The ELT is inFront of you!

ELT (Possibility 1)

ELT (Possibility 2)


YY

If you turn Left and theneedle moves Right

The ELT is inFront of you!

Example:• Turn left• Needle goes

right

ELT (Possibility 1)

ELT (Possibility 2)


YY

Solution:• If you turn Left

and the needle moves Right

• The ELT is inFront of you!

ELT (Possibility 1)


Step 6: Step 6: SHOOTSHOOT

Use your DG to determine a bearing to the target & follow it

You may need to fly through a zone of signal dropout

Be watchful for signs of signal passage• If you get signal passage, consider using the “pinpointing

the target” techniques listed in this presentation

Frequently repeat the FULL SIX STEPS to ensure you are heading in the right direction and that you didn’t inadvertently over fly the ELT

N

SE

W

45135

225

315

How A L-Tronics DF Unit How A L-Tronics DF Unit Works: Summary Works: Summary

Two Main Modes of Operation• RECeive• DF

RECeive Mode is a Strength Meter• Left is low, right is high

DF Mode Centers on Signal• Always points to the signal • Use a Turn to Tell when solving ambiguity

Aircraft and ground units work the same way

QUESTIONS?


ReflectioReflectionsns

Reflections of an ELT signal work just like a flashlight off of a mirror

Any flat, hard, or wet object can cause signal reflections

• Mountains, especially cliff faces• Hangars and other metal structures• Wet grass or ground• Snow• Large bodies of water or ice

Power lines can also have a large effect on a low-powered signal such as an ELT


Beating Beating ReflectionsReflections

Check your sensitivity at half-scale or lower• But ensure that its high enough to receive adequate signal

Reflections will generally be weaker than the most direct path to the target

Following reflections will generally take your closer to the target

If sensitivity is set to minimum, try DFing on a different frequency

• For example, if you are trying to locate an actual ELT on 121.5 MHz, try locating it on 121.6 or 121.775 MHz when you get close

When all else fails, fly somewhere else to get a good DF bearing-or try that at the first sign of problems!


Carrier-Only Carrier-Only SignalsSignals

• You don’t always need to hear the ELT or EPIRB to find it– A carrier-only signal may be broadcasting with no audible

sweep• This is especially true with low or old batteries, damaged

ELTs, or spurious transmissions• You can identify a carrier-only signal by DEFLECTION• If it looks like you’re finding an ELT, even if you can’t hear it,

you have good DEFLECTION• Good needle deflection generally indicates a signal that is

strong enough to DF• Compare your deflection to another frequency

– If you are using 121.5 MHz, try it on 121.775 MHz• If deflection is the same in both frequencies, you DON’T have

a signal, just random noise (or your DF unit may be broken)• If deflection is different, keep at it! You have a signal.• If a signal is only received on 243 MHz, it may be a

malfunctioning antenna (e.g., an FAA tower). If you DF to the location (particularly on or near an airport) and you keep ending up at an antenna, investigate. Find out who owns the antenna and its purpose. Inform the IC and let the controlling agency troubleshoot the problem.


Vertical Vertical Reflections & Reflections &

Signal DropoutSignal Dropout

The transmission pattern (similar to the reception pattern of the DF antennas, only for transmission) of an ELT is not a perfect circle or sphere (especially in the profile view)

It has lobes, or, stronger and weaker points This is accentuated when the ELT is

transmitting from a location above the surrounding ground

When you get a good DF heading and the signal fades or drops out completely you may just be outside of one of the signal lobes

When you reacquire the signal, it should be stronger than when you lost it (if its not, you’re probably going in the wrong direction!)


Signal Signal Dropout Dropout

If you encounter a signal dropout, continue to fly on your last good DF heading

You should reacquire the signal in a few minutes• Actual time will depend upon your distance to the target

If you are unable to reacquire, return to where you last heard the signal and re-DF

NO SIGNALNO SIGNAL

SIGNALSIGNALHEARDHEARD


Signal Signal StrengthStrength

The rate of change in signal strength increases as you get closer to the transmitter, and RECeive mode or the STRENGTH window measures signal strength

This is due to Maxwell’s inverse square law:• When you double the distance from an object, the energy it you

receive from it is 1/4 of what you originally received, or the inverse square: 1/(22) = 1/4

– After Scottish Physicist James Clerk Maxwell, 1831-1879 This is an inverse exponential relationship You will therefore need to turn down the sensitivity to

keep the unit at half scale in the RECeive mode or STRENGTH window much more often as you get close to the source of the signal

• This should let you know that you’re getting close


Signal Strength Rate of Signal Strength Rate of ChangeChange


Cone of Cone of ConfusionConfusion

Antennas receive best when the “pole” is perpendicular to the signal (a 30 dB loss for cross-polarized)

When you approach the directly overhead position on an ELT, your DF will become unreliable

• It may swing left and right• It may center regardless of your heading

You should practice to see what this “station passage” reading looks like

• It is similar to crossing a VOR

Cone ofConfusion


Reception in the Reception in the “Cone of Silence”“Cone of Silence”

antenna

GOOD

POOR

You may also get a significant drop in ELT signal since the antennas receive poorly directly off of their tips (a 90 dB loss)

Although called a cone of silence, you will probably only see & hear a large decrease in signal instead of complete silence


Pinpointing the Pinpointing the ELTELT

If you get a station passage indication, make an approximate 180 degree turn and DF back to the target

Repeat this process using different approach angleseach time, remembering that your path may be curved due to wind (like uncorrected NDB holding)

The point where station passage is received several timesshould be the location of the target

1

2

3


Pinpointing the Pinpointing the ELTELT

After you think you have the target located

• make a low pass over the suspected location and visually scan

• if signal strength decreases significantly or drops out, climb back and try again

• this is not the target: sometimes false targets will appear due to reflections or other interference

If you hear the ELT at low altitude, you probably have the right place

• a low pass down a runway might be a good idea if you suspect a particular airport

QUESTIONS?

Becker SAR-DF 517Becker SAR-DF 517 Completely different theory of

operation from L-Tronics DF• Pseudo Doppler Shift• Beyond the scope of this course• The advanced ELT course has an

explanation

Easy to use Displays a delayed average

heading to the beacon Can be used on 121.5, 243.0, or

406.025 MHz Able to process newest ELTs,

EPIRBs, & PLBs

Becker OperationBecker Operation

PowerModePageTuneSquelchDFLocate

PowerPower

POWER Press the ON/OFF button—unit should power up and illuminate

Be prepared to execute the next steps…

If you’re not fast enough, you may need to recycle power (turn it off and back on)

ModeMode

MODE Using the PAGE knob (upper right knob), select:

EMERGENCY for an actual SAR or TRAINING for a training mission This setting can only be changed on

power up Recycle power to change the Mode After setting EMERGENCY or

TRAINING, just WAIT until the unit automatically goes to the next page

The “wait time” is about 15 seconds

Don’t push any buttons or turn any knobs during this period

PagePage

Use the PAGE knob to cycle to desired page Page 1 is most like an ADF Page 2 is good for forward quarter only Page 3 is most easily read by the entire crew,

but only in relative bearing

TuneTune

The lower-right +/- knob changes the frequency

You want 121,500 for an actual SAR or 121,775 for training

You can alternately use 243,000 or 243,550 respectively

You will only be able to select training frequencies while in the training mode

Similarly, you can only select actual SAR frequencies in the emergency mode

156,800 is for Marine Band Channel 16 EPIRBs

Notice the commas: the Becker is made in Europe; the commas replace a decimal point

SquelchSquelch

Adjust the squelch knob on the upper left of the unit

The squelch knob may be marked SQL or DIM (depending when your Becker was made)

Adjust the small triangle arrow until it is pointing barely above the solid bar

The solid bar represents static or ambient noise, but you will want to listen and make sure that the “static” is not actually a signal

When trying to acquire a signal, you may want the squelch all the way down

You may also want to do this to make sure you can hear audio from the Becker

Turn the lower left knob to adjust the volume to a comfortable listening level

Squelch Knob

Squelch Setting Squelch Setting TriangleTriangle

Ambient Noise Ambient Noise LevelLevel

DF (Direction Find)DF (Direction Find) Follow the relative bearings to the ELT Use homing procedures like an ADF Correct for strong winds, if known Remember that these are RELATIVE bearings

with the nose of the aircraft being 360°/ 000° !!! If you are showing a >006> that means turn right

6° If the unit shows <354<, then turn LEFT 6° This is similar to a fixed-card ADF “Rub The Tub” RB + TH = TB Relative Bearing + True Heading = True Bearing This is also true if we replace magnetic bearing

and heading instead of the trues: RB + MH = MB Therefore if the Becker DF indicates >010> and

you are flying a 270° heading, the magnetic bearing of the ELT is 280°. Add right, subtract left.

Becker Direction Finding Becker Direction Finding NotesNotes

The clear marbles indicate when the Becker first and last receives the ELT signal in its circle

Watching the clear marbles will give you an indication of how coherent your DF solution is

• The marbles will always jump around; if they jump around a LOT you don’t have a good DF

• You can test this by seeing what your indications are when you reduce the squelch enough to “DF” static

• The clear marbles will jump all over the place

• Static can sometimes look like a carrier-only signal

The dark marble should be fairly stable on an actual signal because of signal-averaging software

>020>

DARK MARBLE

CLEAR MARBLES

LocateLocate

After flying over the ELT, you should get a “station passage” indication

Turn around and re-DF to locate the target

This is similar to locating with the L-Tronics DF

If you keep the signal at 090 or 270, you can fly a “turn around a point” using the DF

If the target isn’t visually significant, this will give your Scanner(s) the opportunity to put eyes on the target

Bearing on More than Bearing on More than One TransmitterOne Transmitter

If bearing from a long distance, the DF will be pointing at the middle of the two transmitters

This is because the Becker averages the signals it gets

Exactly in the middle between two transmitters, the DF will display an unusable bearing value

The clear marbles will swing WIDE (180 degrees or more) when in the middle of 2 averaged signals

Exactly over one transmitter the DF will be pointing to another (garbling cone)

Tactic for this situation: don’t fly the approach exactly following the indicated averaged bearing: fly about 20 degrees left or right

Becker ThoughtsBecker Thoughts

The Becker unit is not as sensitive as the L-Tronics DF, so you must be significantly closer to the ELT to get initial signal

Because it uses averaging functions, it will not instantaneously point to an ELT like the L-Tronics unit—there is defnitely a delayed raction

The displays on the Becker lead you to believe that it is a pseudo-RMI or ADF type pointer. This is not the case. Even when the complete circle (page 1) is displayed, the arrow only indicates left or right, NOT how much (such as an ADF). The same is true for the “pie” display, page 2

Look to the “dark marble” to indicate the relative direction of the signal; this acts as an ADF-type pointer

If you do not have an operable training beacon to practice with, pick an AWOS, ASOS, or other continuously-transmitting source that is within the training frequency range. If you tune it in (see the manual, training mode only) you can DF it. A caution with this method, however, is that an AWOS transmits at least 250 times the power level of an ELT. This makes DFing an AWOS much easier than an ELT

Be careful with the unit as it costs roughly $10,000. MAKE SURE THE UNIT IS OFF DURING ENGINE START/SHUTDOWN. Some installations have the DF independent of the avionics master and the unit is sensitive to surges from start/shutdown.

The complete user manual is available at http://www.beckerusa.com


After Locating The After Locating The ELTELT

After location, coordinate with ground teams to bring them on-scene

Use radio communication and relay GPS coordinates

Pick up the ground team at a predetermined location and lead them to the target

Alternately, coordinate a new pick up point on the radio

Practice your air-to-ground coordination skills often

• try it both with and without radio communication

Air-to-ground is CAP’s best unique ES skill!

Many times the ELT is located at an airfield where it is easier for you to land and locate the ELT than it is to get a ground team to the scene

You can use a hand-held radio or hand-held DF unit

The most commonly used handheld DF in CAP is the Little L-Per

You did remember to put one of these (with fresh batteries) in the aircraft before you left, didn’t you?

DF upon DF upon LandingLanding

Six Steps•Receive•Half•DF•Center•Turn•Shoot

Little L-Little L-PerPer

Use Little L-Per or… Use Body Shielding With any hand held aviation band radio, you can

locate an ELT A Jetstream radio also works great Same concept as wing null method, you are just

using your body to block the signal to the antenna When you get very close, there will be too much

signal to get a null Use Frequency Offset Method—try 121.6 instead of

121.5 As you home in, tune in 121.6—you can tune

further away the closer you get

OK, which of these planes is OK, which of these planes is it in?it in?

How To Body Shield: How To Body Shield: The NullThe Null

NULL!

ELT No Signal To Your Receiver

• The Sound Gets Softer!• The ELT Is Directly To Your Back• Throw your thumb over your shoulder to

point to the ELT

SIGNAL

Once you’ve narrowed the suspects down to one or two aircraft (usually side-by-side), remove the radio’s antenna and hold it next to one of the ELT antennas

Turn the volume down until you just hear the signal Don’t key the radio’s transmitter with the antenna

removed Move to the other aircraft’s ELT antenna If the signal is stronger you probably have it; if

weaker, its probably the other aircraft May also put an aluminum foil ‘sleeve’ over the

antenna Can also combine this with the frequency-offset

method

Airmobile UDF Team 101Airmobile UDF Team 101

ELTs are usually located in or near the rear of the aircraft. Also look for remote switches.

Single-engine Cessna: right side of the upper baggage area immediately aft of the baggage door

Multi-engine Cessna: left side of the fuselage just forward of the horizontal stabilizer. Accessed through a small push-plate on the side of the fuselage.

Single- and multi-engine Piper: in the aft fuselage. Accessed through a small access plate on the right side of the fuselage.

Single- and multi-engine Bonanza: in the aft fuselage. Accessed through a small access plate on the right side of the fuselage.

Large piston twins (e.g., King Air) and small jets: if installed its probably in the rear section. No visible antenna. May have a small round push-plate that lets you manipulate the ELT switch.

OK, where is the OK, where is the thing?thing?

(IN the aircraft!)(IN the aircraft!)

Silencing the ELTSilencing the ELT

The preferred method is to have the owner (or someone designated by the owner) turn it off and disconnect the battery

Second best is to just turn it off• The owner may put the switch to ‘Off’ • This may not always work since a malfunctioning

switch could be the problem• If this is done, listen to 121.5 to ensure the beacon has

been deactivated and that it doesn’t go off again• Remind the owner he will need a new battery if the ELT

has been transmitting for more than an hour

A “foil tent” is seldom used–it is temporary and last resort

Ensure that the owner is notified that the ELT was disabled

If you can’t get a phone number, you can place a note on the aircraft (not the window)

Silencing the Silencing the ELTELT

WARNING! to prevent interference with a bona fide

emergency and with the Search and Rescue Satellite System,

YOUR ELT/EPIRB HAS BEEN DEACTIVATED!by: C.A.P Search & Rescue Team

For Further Information, Contact: name, phone #

Per CAP regulations and trespassing laws, CAP members will not enter private property and should not do anything that could cause harm or damage to the distress beacon or aircraft/vessel

CAP members do not have the authority to trespass onto private property, either to gain access to the aircraft or to enter the aircraft to gain access to the ELT

Entry to the ELT should be made by the owner or operator or law enforcement

A transmitting ELT is under the legal authority of the FCC, and federal law requires that it be deactivated ASAP (a crashed aircraft is under the authority of the NTSB)

Besides the owner/operator, some owners give FBO personnel permission to enter their aircraft

Legal Legal IssuesIssues

While entry upon private property may be justified if such an act is for the purpose of saving life, every effort should be made to obtain the controlling agency's and/or the property owner's consent

If you need entry onto private property in order to search for an ELT, law enforcement authorities such as local police, the county sheriff's office or game wardens may be contacted for assistance.

Normally, local law enforcement officials are happy to assist you; if they are not familiar with CAP and your responsibilities, a simple explanation often suffices

If this doesn't work, try having your IC calling AFRCC and have them explain the situation


The most important aspect is the manner in which you approach the matter

The local civil authorities are in charge, if they tell you go home, then phone the IC and/or AFRCC and close the mission



QUESTIONS?QUESTIONS?

Good Luck and Good Luck and Good Hunting!Good Hunting!

Mission Aircrew Course Chapter 10: Electronic Search Patterns (Mar 2007)

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Transcript of Mission Aircrew Course Chapter 10: Electronic Search Patterns (Mar 2007)