Air Operations Branch Director Course

Air OperationsAir OperationsBranch Director CourseBranch Director Course

Planning Planning Air-to-Ground and Air-to-Ground and

High-Bird High-Bird Communications Communications

OperationsOperations

Calculating Line of SightCalculating Line of Sight

U.S. AIR FORCE AUXILIARY

U.S. AIR FORCE AUXILIARY

The ProblemThe Problem

VHF Communication is limited to line of VHF Communication is limited to line of sightsight

An aircraft at altitude has a great An aircraft at altitude has a great advantage over ground-based radio advantage over ground-based radio stations, but it is limitedstations, but it is limited

CaveatCaveat

VHF is basically line-of-sight limited, but…VHF is basically line-of-sight limited, but…– VHF Radio signals do actually bend slightly VHF Radio signals do actually bend slightly

towards the Earth surface, so actual reception towards the Earth surface, so actual reception range is about 15% better than geometric line range is about 15% better than geometric line of sightof sight

General Factors Impacting General Factors Impacting RangeRange

TerrainTerrain

Signal strength / radio conditionSignal strength / radio condition

WeatherWeather

Related ProblemRelated ProblemELT Airborne ReportsELT Airborne Reports

When prosecuting an ELT search, we may When prosecuting an ELT search, we may get reports of aircraft that did get reports of aircraft that did or did notor did not hear the ELThear the ELT

We can take into account the altitude of We can take into account the altitude of the reporting aircraft and draw circles on a the reporting aircraft and draw circles on a map representing line of sightmap representing line of sight

Related ProblemRelated ProblemELT Airborne ReportsELT Airborne Reports

ELT Airborne Reception RangeELT Airborne Reception Range

Variables Variables – Signal strength Signal strength

(recall that, at best, (recall that, at best, ELTs transmit at only ELTs transmit at only 300 mA)300 mA)

– WeatherWeather– TerrainTerrain– Condition of the Condition of the

beacon and beacon and antennaantenna

Altitude AGL Altitude AGL (1000 ft)(1000 ft)

Line of sightLine of sight(NM)(NM)

11 3636

22 5252

33 6363

44 7272

55 8181

1010 114114

1515 140140

2020 162162

2525 180180

3030 198198

3535 214214 Ref: AFRCC and Canadian SAR calculations

Our LOS Estimation TableOur LOS Estimation Table

We’ll introduce our own estimation tableWe’ll introduce our own estimation table– We’ll estimate slightly longer distances than We’ll estimate slightly longer distances than

the RCC table the RCC table The RCC table seems conservative (perhaps The RCC table seems conservative (perhaps because ELT signals aren’t particularly strong)because ELT signals aren’t particularly strong)

Other references seem to indicate that 15% over Other references seem to indicate that 15% over geometric line of sight would be reasonablegeometric line of sight would be reasonable

LOS Estimation TableLOS Estimation Table

Altitude Altitude AGL (ft)AGL (ft)

RCC Line of sightRCC Line of sightestimate (NM)estimate (NM)

Geometric Geometric Line of sight Line of sight (NM)(NM)

Geometric Line of Geometric Line of sight + 15% (NM)sight + 15% (NM)

1,0001,000 3636 3434 3939

2,0002,000 5252 4848 5555

3,0003,000 6363 5959 6868

4,0004,000 7272 6868 7878

5,0005,000 8181 7676 8787

6,0006,000 8383 9595

7,0007,000 9090 104104

8,0008,000 9696 110110

9,0009,000 102102 117117

10,00010,000 114114 107107 123123

Sample ProblemSample Problem

Several aircraft on a search mission are Several aircraft on a search mission are assigned to an altitude of 1000 ft AGLassigned to an altitude of 1000 ft AGL

How far away from the mission base can the How far away from the mission base can the aircraft go and still be in communications range?aircraft go and still be in communications range?

Assume terrain is no factorAssume terrain is no factor

Assume no repeaters are in useAssume no repeaters are in use

Answer: 39 NM


An airborne repeater is being sent to orbit An airborne repeater is being sent to orbit a station at an altitude of 5000 ft AGLa station at an altitude of 5000 ft AGL

Assume flat terrain for entire service areaAssume flat terrain for entire service area

What is the radius of the repeater’s service What is the radius of the repeater’s service area on the ground?area on the ground?

Answer: 87 NM

What about air-to-air range?What about air-to-air range?

Can two aircraft talk to each other if they can Can two aircraft talk to each other if they can both “see” the same point on the horizon?both “see” the same point on the horizon?

Yes, even if they are at different altitudesYes, even if they are at different altitudes– Think of the point as defining a plane-surface touching the Think of the point as defining a plane-surface touching the

Earth’s sphere; anyone on that surface will see the point as Earth’s sphere; anyone on that surface will see the point as being on the horizonbeing on the horizon

– Anyone on or above the plane will have an unobstructed line Anyone on or above the plane will have an unobstructed line of sight to anyone else on or above the planeof sight to anyone else on or above the plane

Computing Air-to-Air RangeComputing Air-to-Air Range

The horizon point The horizon point represents the represents the line of sight limit line of sight limit for each aircraft for each aircraft So, we can add So, we can add together the together the line of sight line of sight distances distances for the two for the two aircraft – aircraft – i.e. they i.e. they can talk to can talk to each othereach other

Overhead view


An airborne repeater is being sent to orbit a An airborne repeater is being sent to orbit a station at 8000 ft AGLstation at 8000 ft AGL

Search aircraft are assigned 1000 ft AGL sorties Search aircraft are assigned 1000 ft AGL sorties

How far away can the search aircraft operate How far away can the search aircraft operate and still be in-range of the airborne repeater?and still be in-range of the airborne repeater?

Assume terrain is no factorAssume terrain is no factor

Answer: 39 NM + 110 NM = 149 NM

What about terrain?What about terrain?

Determine MSL altitudes for terrainDetermine MSL altitudes for terrainNote altitude of terrain between aircraft radio Note altitude of terrain between aircraft radio stationsstations– So long as aircraft are well above terrain, ignore So long as aircraft are well above terrain, ignore

anything near to aircraftanything near to aircraft

Find the highest point in middle area (roughly Find the highest point in middle area (roughly the middle third between the aircraft)the middle third between the aircraft)Use the altitude of that highest point as the basis Use the altitude of that highest point as the basis from which to calculate the effective height of from which to calculate the effective height of the aircraft for the purpose of determining line of the aircraft for the purpose of determining line of sightsight


Example: high terrain between aircraftExample: high terrain between aircraft– Use the altitude of the highest ground between as the Use the altitude of the highest ground between as the

“imaginary surface” from which we’ll compute altitude“imaginary surface” from which we’ll compute altitude– Aircraft must fly high to stay in sight of each otherAircraft must fly high to stay in sight of each other


Another example: lower altitude between Another example: lower altitude between aircraftaircraft


Aircraft 1 (high-bird) is orbiting at 4000 ft MSL over a Aircraft 1 (high-bird) is orbiting at 4000 ft MSL over a point with a surface elevation of 1000 ft MSLpoint with a surface elevation of 1000 ft MSLAircraft 2 is searching at 1000 ft AGL over terrain at Aircraft 2 is searching at 1000 ft AGL over terrain at 2000 ft MSL2000 ft MSLTerrain in-between is no higher than 1500 ft MSLTerrain in-between is no higher than 1500 ft MSLIf the aircraft are 100NM apart, can they communicate?If the aircraft are 100NM apart, can they communicate?

3000 MSL

4000 MSL

1 2

Sample Problem (cont.)Sample Problem (cont.)

Prevailing terrain is 1500ft MSLPrevailing terrain is 1500ft MSL

Aircraft 1 is at 4000ft MSL or 2500ft over terrainAircraft 1 is at 4000ft MSL or 2500ft over terrain– Line of sight for aircraft 1 is 62 NMLine of sight for aircraft 1 is 62 NM

Aircraft 2 is at 3000ft MSL or 1500ft over terrainAircraft 2 is at 3000ft MSL or 1500ft over terrain– Line of sight for aircraft 2 is 47 NMLine of sight for aircraft 2 is 47 NM

Total line of sight is 109 NMTotal line of sight is 109 NM

Terrain in MinnesotaTerrain in Minnesota

Line of sight throughout most of Minnesota Line of sight throughout most of Minnesota can be estimated reasonably with a flat can be estimated reasonably with a flat terrain modelterrain model

Watch out, however, for some areas like Watch out, however, for some areas like river valleysriver valleys

Aircraft Platform-Specific FactorsAircraft Platform-Specific Factors

Aircraft AttitudeAircraft Attitude– Due to the placement of the VHF antenna on the Due to the placement of the VHF antenna on the

bottom of the aircraft, aircraft attitude will be bottom of the aircraft, aircraft attitude will be important. important.

– Straight and level flight usually will give good results. Straight and level flight usually will give good results. – A banking aircraft will block the signal in the direction A banking aircraft will block the signal in the direction

of the bank. of the bank. – Climbing and descending will also influence Climbing and descending will also influence

propagation. propagation. A climbing aircraft will block the signal with the tailA climbing aircraft will block the signal with the tailA descending aircraft will block the signal with the nose.A descending aircraft will block the signal with the nose.

Aircraft Platform-Specific FactorsAircraft Platform-Specific Factors

Propagation PatternPropagation Pattern

Propagation is best to either side of the Propagation is best to either side of the aircraft. aircraft.

Propagation off the nose is impacted due Propagation off the nose is impacted due to the antenna placement and the to the antenna placement and the interference of the nose and engine. interference of the nose and engine.

Flight PlanningFlight Planning

Remember aircrew should be given MSL Remember aircrew should be given MSL altitude for station altitude for station Plan timing of high-bird sortie relative to Plan timing of high-bird sortie relative to other operations (we want it there when it other operations (we want it there when it is needed)is needed)Remember a C172 sortie is limited to 3 Remember a C172 sortie is limited to 3 hours; aircraft will need to periodically land hours; aircraft will need to periodically land and refueland refuel

Flight Planning - IFRFlight Planning - IFR

As an alternative to executing a published As an alternative to executing a published holding pattern, the aircraft can request ATC for holding pattern, the aircraft can request ATC for a clearance to fly a block of airspace a clearance to fly a block of airspace corresponding to an elongated holding pattern corresponding to an elongated holding pattern (with a 2 minute in-bound leg). (with a 2 minute in-bound leg). The advantage of flying an elongated holding The advantage of flying an elongated holding pattern is two-fold:pattern is two-fold:– Reduces crew fatigueReduces crew fatigue– Reduces the amount of time with the aircraft in a bank Reduces the amount of time with the aircraft in a bank

impacting radio signal propagationimpacting radio signal propagation

High-Bird TypesHigh-Bird Types

Airborne repeaterAirborne repeater– Advantages: automatic and rapid, everyone hearsAdvantages: automatic and rapid, everyone hears– Limitations: only one aircraft in fleet equipped; cannot Limitations: only one aircraft in fleet equipped; cannot

offer continuous serviceoffer continuous service

Manual message relay (stations call “high-bird” Manual message relay (stations call “high-bird” and request message relay)and request message relay)– Advantages: can take advantage of ground-based Advantages: can take advantage of ground-based

repeaters to further extend effective rangerepeaters to further extend effective range– Limitations: slow and awkward, traffic cleared slowly, Limitations: slow and awkward, traffic cleared slowly,

stations step on each other trying to call high-birdstations step on each other trying to call high-bird

Combined – one aircraft provides both servicesCombined – one aircraft provides both services

High-Bird Crew PlanningHigh-Bird Crew Planning

An airborne repeater requires minimal crew (pilot An airborne repeater requires minimal crew (pilot plus perhaps one to monitor equipment)plus perhaps one to monitor equipment)A high-bird providing manual message relay A high-bird providing manual message relay should have a crew of three (pilot, radio-should have a crew of three (pilot, radio-operator, and radio-operator/scribe)operator, and radio-operator/scribe)– Manual message relay is a heavy workloadManual message relay is a heavy workload

Lots of time logging and writing down messagesLots of time logging and writing down messagesHeavy frequency congestion from high-bird vantage pointHeavy frequency congestion from high-bird vantage point

Other limiting factors:Other limiting factors:– Weight and balance limits for aircraftWeight and balance limits for aircraft

What about ground-based What about ground-based repeaters?repeaters?

Remember that they are often on high-Remember that they are often on high-ground and on a tall buildingground and on a tall building

We can treat them like low aircraftWe can treat them like low aircraft

Use estimate of about 25NM line of sightUse estimate of about 25NM line of sight

Distances Across MinnesotaDistances Across Minnesota

PKD

MN/NW

DLH

MN/SW

STP

MN/NE

MN/SE

MN/N

MN/WC114NM

130NM

150NM

152NM

145NM

115NM

107NM

MKT

60NM

119NM

125NM

152NM

INL

122NM

114NM


We have a mission base at STP and we We have a mission base at STP and we want to communicate with an aircraft at want to communicate with an aircraft at 1000 ft AGL in the northwest corner of the 1000 ft AGL in the northwest corner of the statestate

If we put a high-bird over PKD at 11,000 ft If we put a high-bird over PKD at 11,000 ft MSL, will that provide the communications MSL, will that provide the communications that we need?that we need?

Sample Problem (cont)Sample Problem (cont)

Distances:Distances:– PKD to MN/NW: 152 NMPKD to MN/NW: 152 NM– PKD to STP: 145 NMPKD to STP: 145 NM


Terrain:Terrain:– At PKD: 1443 MSLAt PKD: 1443 MSL– At MN/NW: 795 MSLAt MN/NW: 795 MSL– At STP 705: MSL (in river valley)At STP 705: MSL (in river valley)– Between PKD and MN/NW: ~1200 MSL (we’ll Between PKD and MN/NW: ~1200 MSL (we’ll

round that to 1000 ft)round that to 1000 ft)– Between PKD and STP: ~1200 MSLBetween PKD and STP: ~1200 MSL

(we’ll round that to 1000 ft)(we’ll round that to 1000 ft)


Air-to-air communication between PKD Air-to-air communication between PKD and MN/NW should be no problemand MN/NW should be no problem– High-bird is at about 10,000 ft above terrain, High-bird is at about 10,000 ft above terrain,

with a line of sight of 123 NMwith a line of sight of 123 NM– Search aircraft is 1000 ft above terrain with a Search aircraft is 1000 ft above terrain with a

line of sight of 39 NMline of sight of 39 NM– Combined line of sight is 162 NM which is Combined line of sight is 162 NM which is

less than distance of 152 NMless than distance of 152 NM

Sample Problem (cont)Sample Problem (cont)Direct air-to-ground communications with STP has Direct air-to-ground communications with STP has problemsproblems– High-bird is at about 10,000 ft above terrain, with a line High-bird is at about 10,000 ft above terrain, with a line

of sight of 123 NM, which is less than distance of 145 of sight of 123 NM, which is less than distance of 145 NMNM

– The location of STP in a valley wouldn’t help eitherThe location of STP in a valley wouldn’t help either

There is, however, a repeater about 2 miles There is, however, a repeater about 2 miles southeast of STPsoutheast of STP– Its line of sight can be estimated at 25NM and its Its line of sight can be estimated at 25NM and its

distance to PKD just a couple miles furtherdistance to PKD just a couple miles further– Combining the line of sight of the aircraft with that of the Combining the line of sight of the aircraft with that of the

repeater, we have 123 NM + 25 NM = 148 NM, which is repeater, we have 123 NM + 25 NM = 148 NM, which is just about exactly distance from the repeater to PKDjust about exactly distance from the repeater to PKD


Determination: We can establish the Determination: We can establish the required communicationsrequired communications– Our solution uses a ground-based repeaterOur solution uses a ground-based repeater– This requires that the high-bird provide This requires that the high-bird provide

manual message relay manual message relay (i.e. we are not using the airborne repeater)(i.e. we are not using the airborne repeater)

Final NotesFinal Notes

These line of sight estimates are inexactThese line of sight estimates are inexact– Atmospheric conditions can impact results actually Atmospheric conditions can impact results actually

seenseenSome reports indicate we can sometimes do better than the Some reports indicate we can sometimes do better than the numbers in our estimation tablenumbers in our estimation table

– Its difficult to fully account for terrain without running a Its difficult to fully account for terrain without running a computer programcomputer program

This material should, however, help you plan This material should, however, help you plan operations that require us to stretch our lines of operations that require us to stretch our lines of communicationscommunications

Questions?Questions?

Air Operations Branch Director Course

Documents

Transcript of Air Operations Branch Director Course