ELT Homing Air and Ground Search Prepared By Terry Cooper
Visual Search 1 500 AGL: Where s the crash?
Visual Search 2 How about now? (200 AGL)
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 (fixed wing).
Typical ELT Location ELT
SARSAT/COSPAS Satellites on Polar orbits (LEOS) Satellite orbits take 100 minutes Monitoring 121.5*, 243*, and 406 MHz Primarily designed for 406MHz Relay ELT signals to local user terminals (ground stations) Doppler shift used to find possible location of the beacon 121.5 and 243 monitoring will cease by Feb. 2009
Signal Confidence SARSAT hits are given a confidence value. Confidence Accuracy 1 50+ Miles 2 20-50 Miles 3 5-20 Miles 4 0-5 Miles
Comparing ELT Types TYPE 121.5 406 Location Accuracy 12nm 2nm Coverage Local Global Signal Power.1W 5W Alert time 1.5-2.0 Hours Instantaneous Doppler Location 2 Passes 1 Pass
Radio Basics
Radio Direction Finding Two methods of RDF Triangulation (signal strength, bearing) Homing (signal strength and direction)
Tools of the Trade Little L-Per Handheld H Antenna
Vehicle Mount Quad Right Left Fore Aft Magnetic Vehicle mount antennas Left/Right Fore/Aft
A/C External Antennas Temporary Strut mount installation Permanent Belly mount installation
Little L-Per How it works 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 DF Mode Antennas switched 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 well with moving vehicle or aircraft
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
Handheld RDF Use L-Per on DF mode Find centres (there should be two) More than two centres use REC mode Take multiple bearings to the target Triangulate with bearings Watch for sources of error
CENTRE
CENTRE
CENTRE
CENTRE! CENTRE
CENTRE
CENTRE
CENTRE
CENTRE
CENTRE! CENTRE
CENTRE
CENTRE
CENTRE
CENTRE
CENTRE! CENTRE
Triangulation
Using the Quad Little L-Per is always in 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
Using the Quad Right Left Fore Aft Right Left Fore Aft Right Left Fore Aft Target in Front Target Beside Target in Back
Using the Quad Right Left Fore Aft Right Left Fore Aft Right Left Fore Aft Target Left Target Front or back Target Right
Boxing the target (Quad) Switch in Fore/Aft: needle right Switch in Right/Left: Needle Left Leave switch in Fore/Aft
Boxing the target (Quad) Switch in Fore/Aft: needle centres Switch in Right/Left: Needle Left Mark map
Boxing the target (Quad) Switch in Fore/Aft: needle centres Switch in Right/Left: Needle Left Find a road to left
Boxing the target (Quad) Switch in Fore/Aft: needle centres Switch in Right/Left: Needle Left Mark map
Boxing the target (Quad) Switch in Fore/Aft: needle centres Switch in Right/Left: Needle Left Entire track should be done Without stopping vehicle for Heading checks, errors are Reduced by vehicle motion. Get as close as possible with Vehicle, then proceed on foot with Handheld antenna Additional sides reduces error
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
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.
Boxing the target (air) Fly tracks with needle centred at all times Signal strength increasing, Needle moderately sensitive
Boxing the target (air) Brief turns can be used to confirm station passage. Signal strength very high, Needle very sensitive
Boxing the target (air) Signal strength decreasing, Needle less sensitive
Boxing the target (air) Probable target area
Boxing the target (air) Fly second track perpendicular to first starting roughly in the centre of probable target area. Keep the needle centred
Boxing the target (air) Intersection of tracks is target location Keep the needle centred Call in the ground team.
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.
Aural Null Using aircraft communications radio Procedure A Procedure B
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.
Wing Blanking Using aircraft comms radio Once a signal is picked up: Turn 360 degrees Note audible drop in signal The signal drop indicates that the belly of the a/c points at the target. Repeat the process to triangulate the target. Doesn t work with all antenna installations.
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
Reflection Errors
Hangar/Crash Effects
Hawksbury East (Actual Search) Runway, Grass Metal open front hangars Large Mtce hangar Trees Paved apron
Canyon Effect
Forest Effects
Hills/Mountains
Signal Polarization
Airborne False Targets
Airborne Reflections
Information Sources www.ltronics.com (Maker of Little L-Per) www.cap-es.net (Scott E Lanis) Practice and Experience