Why 406 ELT? • Improved location accuracy and ambiguity resolution • Increased system capacity (i.e. capability to process a greater number of beacons transmitting simultaneously in field of view of satellite) • Increased probability of detection (higher power) • Global coverage • Unique identification of each beacon
406 ELT Specifics • Enhanced system with improved frequency stability at a dedicated frequency. • Beacons transmit a 5 Watt RF burst of approximately 0.5 seconds duration every 50 seconds. The carrier is phase-modulated with a digital message. High peak power increases the probability of detection. The low duty cycle provides a multiple-access capability for a large number of beacons simultaneously operating in view of a polar orbiting satellite, and low mean power consumption. • Digitally encoded message, provide information such as the country of beacon registration, identification of the vessel or aircraft in distress, and optionally, position data from onboard navigation equipment. • An auxiliary transmitter (homing transmitter) is usually included in the 406 MHz beacon to enable suitably-equipped SAR forces to home on the distress beacon
Topics to Explore • Comparison of Standard ELT, ELT Practice Beacons and 406 ELT/EPIRB Beacons • Expected Coverage Range for a 406 ELT at various search altitudes • Expected Coverage Range for the 406 ELT’s (40mw) 121.5 MHz at various search altitudes
Test Plan • Simac “Serach-Pro” 406 Practice beacon operating on 406.025 MHz was placed at French Lick Airport (FRH) • Inbound and outbound test flights were were conducted to the north at AGL altitudes of: • 1000’ • 3000’ • 5000’ • 10,000’ • Flights conducted on 3 separate sorties on July 8th & 9th 2009
Aerial Test Platform • Aerial survey was flown in N738CP a Cessna 182T with Garmin G1000 FMS Aircraft • Becker DF 715 receiver used to identify the 406 beacon reception by observing acquisition and loss of data reception • Garmin VHF Com was used to identify acquisition and loss of the 121.775MHz homing transmitter Becker 121 DF Antenna Becker 406 Antenna Becker 121MHz DF Antenna
Route Surveyed • The location was chosen for its low terrain and geographic separation from the NESA training areas in order to avoid false hits from other training beacons. • Routes were flow using the G1000 GPS and KAP140 Autopilot in OBS NAV mode on bearings of 180 and 360 to and from the north of French Lick (FRH) airport at each altitude previously mentioned. • The same course was flow on to the south of at 1000’ and 3000’ AGL and the results were similar.
Observations • Better reception going away from the 406MHz beacon than going toward • Suspect that this has to do with the rearward placement of the 406 antenna • Better reception as altitude increases but above 5000’ AGL the benefit begins to diminish • Up to 10,000’ AGL can receive 406MHz as far as 50NM from the beacon • Up to 10,000’ AGL can receive 121MHz homing signal as far as 22NM from the beacon • Tangent reception from the side on the Becker antenna was virtually identical to results of ahead or behind
Conclusions • Aircrew should approach search area above 5000’AGL initially • Once the 406 signal has been acquired, turn to the suggested heading and descend while approaching the area • As ambiguity decreases make minor course corrections and continue decent. • Monitor 121.5 (or 121.775 MHz) on the Com radio • Final DF using 121.5 (or .775) is most effective at close range.
Limitations and Shortcomings • Limited Dataset • Limited to one Aircraft and radio system • Did not get L-Tronics data • Battery life of ELT Practice Beacon unknown • 2004 Battery • Would like to compare 406 and 121.775 beacon from the same location simultaneously