A fatal general aviation accident in which four badly injured survivors' lives were put at risk by the failure of the aircraft's emergency locator transmitter has worried the US National Transportation Safety Board.
The NTSB has voiced its concern that the widely used system is vulnerable to a similar failure in future.
The 9 August 2010 accident involved a de Havilland Canada DHC-3T single-turbine floatplane carrying nine people between remote fishing lodges in Alaska. It hit high ground in marginal visual meteorological conditions, killing the pilot and four passengers, and badly injuring the surviving four.
Almost 4h after its departure, a telephone inquiry by a manager at the departure point asking about the aircraft's anticipated return, established that the aircraft had not arrived at its destination. The NTSB found that it had crashed about 15min after take-off in high wooded ground 30km (18.6 miles) north of Dillingham in southern Alaska.
A search by volunteer aviators along the planned route, with no help from the aircraft's transmitter, established the position of the wreckage, but the weather closed in and paramedics could not access the site until the following day to recover the survivors.
The NTSB found that the Artex ME406 ELT, designed to broadcast signals via an externally mounted antenna, had become separated from its mounting tray and thus from the external antenna, so although the system was triggered by the crash, the signals were not transmitted.
The ELT is designed to send a 406MHz signal relaying the aircraft's position by satellite to emergency centres, but it also transmits a homing signal on the VHF emergency frequency 121.5 MHz for search aircraft to use.
The agency has called for the Federal Aviation Administration to require an immediate check of all general aviation ELTs to ensure that they are mounted according to specification, and in the longer term to determine whether the mounting requirements are sufficiently robust in the light of this accident.