ELT Homing

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ELT Homing

• Air and Ground Search
• Prepared By
• Terry Cooper

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Agenda

• What does a crash look like?
• ELT and Radio basics
• Radio Direction Finding
• Basic search methods - Ground
• Basic search methods - AIR
• Things that will fool you

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What Will A Crashed Airplane Look Like?
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What Will It Look Like? (2)
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Visual Search 1

• 500 AGL Wheres the crash?

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Visual Search 2

• How about now? (200 AGL)

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What is an ELT?

• Low power radio transmitter (50-75mw, 5W on 406)
• 121.5Mhz, 243Mhz (military) or 406Mhz
• Triggered by impact/shock
• 48 Hour battery life
• External and Built-in antennas
• Typically installed in the tail of an aircraft

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Typical ELT Location
ELT
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ELT Types

• TSO C-91 (this is the most common)
• Original spec. for 121.5 ELT
• Reliability problems, poor frequency control
• Poor survivability
• TSO C-91a
• Next generation 121.5 ELT
• Remote control (panel switch)
• More reliable G switch
• Improved frequency control
• Better survivability

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ELT Types Cont.

• 406 ELTs and EPIRBs
• SARSAT/COSPAS designed for 406Mhz Beacon
  frequency
• 5W burst digital signal at 406MHz
• Low power continuous signal on 121.5MHz for
  homing
• Very accurate frequency control
• More reliable G switch
• High survivability
• Identity broadcast
• Possible GPS connection
• Personal Locator Beacons available

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Comparing ELT Types
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Radio Basics

• Radio waves travel somewhat like light
• Direct, Reflected, Absorbed, Refracted
• Slowed and attenuated by ground effect
• Horizontal or Vertical polarization

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Radio Basics
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Radio Direction Finding

• Two methods of RDF
• Triangulation (signal strength, bearing)
• Homing (signal strength and direction)

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Tools of the Trade
Handheld H Antenna
Little L-Per
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Vehicle Mount Quad
Magnetic Vehicle mount antennas
Left/Right
Fore/Aft
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A/C External Antennas
Temporary Strut mount installation
Permanent Belly mount installation
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Little L-PerHow it works

• Two modes of operation
• REC (signal strength)
• DF (signal direction and strength)
• REC Mode (only used for Handheld)
• Antenna forms directional beam (YAGI)
• Left side points to target at highest signal
• Needle indicates signal strength
• Useful for confirming multiple DF centres

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L-Per Works Cont.

• DF Mode
• Antennas switch a high rate
• Needle points to side with strongest signal
• Needle centres with target in front or behind
• Functional with very weak signal (you may not
  hear it)
• Works better with moving vehicle or aircraft

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ELT search basics

• Look for obvious target areas near SARSAT hit
• airports, heliports, Purolator depots
• Look for high ground
• Take numerous bearings
• Box the target or triangulate

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Handheld RDF

• Use handheld radio to listen for signal
• Use L-Per on DF mode
• Take multiple bearings to the target
• Triangulate with bearings
• Watch for sources of error
• Use REC mode to confirm target

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Triangulation
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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CENTRE
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Using the Quad

• Little L-Per is always on DF mode
• While vehicle is moving, average the indication
  (it will be swinging)
• Watch for centre or flip
• Keep needle at about half scale by adjusting
  sensitivity control
• Box the target
• Always look for sources of error

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Using the Quad
Target Beside
Target in Front
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Using the Quad
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Boxing the target (Quad)
Switch in Fore/Aft needle right Switch in
Right/Left Needle Left
Leave switch in Fore/Aft
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Boxing the target (Quad)
Switch in Fore/Aft needle centres Switch in
Right/Left Needle Left
Mark map
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Boxing the target (Quad)
Switch in Fore/Aft needle centres Switch in
Right/Left Needle Left
Find a road to left
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Boxing the target (Quad)
Switch in Fore/Aft needle centres Switch in
Right/Left Needle Left
Mark map
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Boxing the target (Quad)
Entire track should be done Without stopping
vehicle for Heading checks, errors are Reduced
by vehicle motion.
Switch in Fore/Aft needle centres Switch in
Right/Left Needle Left
Get as close as possible with Vehicle, then
proceed on foot with Handheld antenna
Additional sides reduces error
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Closing in

• Reduce L-Per sensitivity
• Fold H antenna
• Use Handheld Radio
• Tune off frequency
• Remove antenna
• Use signal strength meter
• Use these methods for airports or Purolator
  depots where multiple choices of target exist

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Air Search

• RDF Homing
• Use Little L-Per and Strut or belly mount or
  Spotter held antennae
• Similar to ground vehicle RDF with Quads
• Turn to centre, hold to track to target
• Fly perpendicular tracks to narrow target area.

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Boxing the target (air)
Fly tracks with needle centred at all times
Signal strength increasing, Needle moderately
sensitive
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Boxing the target (air)
Brief turns can be used to confirm station
passage.
Signal strength very high, Needle very sensitive
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Boxing the target (air)
Signal strength decreasing, Needle less sensitive
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Boxing the target (air)
Probable target area
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Boxing the target (air)
Fly second track perpendicular to first starting
roughly in the centre of probable target area.
Keep the needle centred
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Boxing the target (air)
Intersection of tracks is target location
Keep the needle centred
Call in the ground team.
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Boxing the target (air)
Additional tracks will refine target location,
reducing search altitude will also narrow the
area.
Some error will still exist due to search
altitude, local terrain, and ELT position.
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Aural Null

• Using aircraft communications radio

Procedure A
Procedure B
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Aural Null

• Procedure B is quicker, less flying
• Accurate navigation is required for either
  procedure
• Signal propagation errors will affect results
• Aircraft radio/antennas have a directional bias.

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RDF in the real world(stuff that will fool you)

• RDF in open areas
• RDF in Hills/Mountains/Wooded areas
• RDF in urban areas
• Effects of wreckage
• Effects of hangars

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Reflection Errors
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Hangar/Crash Effects
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Hawksbury East(Actual Search)
Runway, Grass
Metal open front hangars
Large Mtce hangar
Trees
Paved apron
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Canyon Effect
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Forest Effects
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Hills/Mountains
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Signal Polarization
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Airborne False Targets
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Airborne Reflections
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Information Sources

• www.ltronics.com (Maker of Little L-Per)
• www.CAP-ES.net (Scott E Lanis)

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