VH-MDX’s ELT appears to have had an auto function that would have triggered the ELT when a certain longitudinal ‘G’ value was exceeded as would likely have been experienced during impact.

Aircraft were overhead the Barrington area within minutes of the final received radio call from VH-MDX and searched overhead during the accident night.

No ELT transmissions were reported as being received. Transcripts show that within around 20 minutes of the final received call from VH-MDX a Qantas 747 overhead the Barrington area did not receive ELT transmissions.

Automatic operation of the ELT is contingent on:

– Serviceability of the ELT (battery condition, wiring, installation etc)

– Having the ‘Auto’ arm switch position selected

– The ELT not being damaged during impact.

It is not known if the ELT had a remote arming panel in the cockpit that would allow the pilot to manually turn on the ELT. If not, the ELT would have to be manually switched on at the unit located at the rear of the aircraft or rely on the automatic triggering function.

121.5MHz ELT’s as fitted to VH-MDX had a very poor record of automatic activation during aircraft crashes with one study claiming an activation rate of 12%.