Underwater locator beacon

[1][2][3] Research by the French Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile (BEA) has shown that it has had a 90% survival rate spanning 27 air accidents over the sea.

[4] The ULBs fitted in Air France Flight 447, which crashed on 1 June 2009, were certified to transmit at 37.5 kHz for a minimum of 30 days at a temperature of 4 °C.

After investigating the crash, the BEA recommended that FDR ULBs' transmission period be increased to 90 days and for "airplanes performing public transport flights over maritime areas to be equipped with an additional ULB capable of transmitting on a frequency (for example between 8.5 kHz and 9.5 kHz) and for a duration adapted to the pre-localisation of wreckage" (i.e. with increased range).

[5] On ships built on or after 1 July 2014, underwater locating devices must ensure a regulatory transmission time of at least 90 days.

[7] The National Transportation Safety Board reported a case in 1988, involving an Aerospatiale AS-355F-1 helicopter, when the water switch had accidentally activated during the aircraft's normal operation; as a result, the battery power had been exhausted by the time the accident happened, and the beacon was not emitting the acoustic signal when it needed to do so.