Factual Information 2015:1.6 Aircraft Information/1.6.6 ELT/1.6.6.1
This page contains an extract from MH370/01/15 Factual Information which accompanied the (first) Interim Statement released by The Malaysian ICAO Annex 13 Safety Investigation Team for MH370 on 8th March 2015.
1.6.6.1 Review of Effectiveness of ELTs
In general, ELTs are intended for use at or near the water’s surface, and neither portable nor fixed ELT signals are detectable when the ELT is submerged in deep water. Portable ELTs are equipped with a floatation device and can be activated by immersion in water. For effective signal transmission, the antenna for a fixed ELT must remain above water. Damage to an ELT or its associated wiring and antenna, or shielding by aircraft wreckage or terrain, may also prevent or degrade transmission.
a) A review of ICAO accident records over the last 30 years indicates that of the 257 accidents, only 39 cases recorded effective ELT activation. ELTs were carried in 173 of these cases. This implies that of the total accidents in which ELTs were carried, only 22.5% of the ELTs operated effectively (Appendix 1.6D).
b) The Cospas-Sarsat system has been helpful for search and rescue teams in numerous aircraft accidents on a world-wide basis. Despite these successes, the detection of ELT signals after an aircraft crash remains problematic. Several reports have identified malfunctions of the beacon triggering system, disconnection of the beacon from its antenna or destruction of the beacon as a result of accidents where aircraft was destroyed or substantially damaged. Even when the beacon and its antenna are functioning properly, signals may not be adequately transmitted to the Cospas-Sarsat satellites because of physical blockage from aircraft debris obstructing the beacon antenna or when the antenna is under water.
(Source: Global Aeronautical Distress and Safety System - GADSS6 document)
c) ELTs can be activated automatically by shock typically encountered during aircraft crashes or manually. It is possible for Flight Crew to manually activate the ELT; however existing flight operating procedures do not call for activation of the ELTs until the incident has occurred.
d) The Cospas-Sarsat system does not provide a complete coverage of the earth at all times. As a consequence, beacons located outside the areas covered by these satellites at a given moment cannot be immediately detected, and must continue to transmit until a satellite passes overhead.
e) The global distress beacon detection system, Cospas-Sarsat, no longer detects 121.5 MHz distress signals. Only 406 MHz digital distress beacons are now capable of detection by satellite. Analogue beacon signals may be received by other aircraft within VHF range but there may not be such aircraft within range at the time of beacon transmission and monitoring 121.5 MHz.
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6In the aftermath of the disappearance of MH370, following a multidisciplinary meeting in May 2014, ICAO formed an Ad-hoc Working Group on Flight Tracking with the mandate to develop a Concept of Operation on the sequence of events before and after the occurrence of an accident which should include all identified phases of such a sequence including detection of an abnormal situation, alert phase, distress phase, and search and rescue activities. This Concept of Operation is GADSS.
Source: Malaysian ICAO Annex 13 Safety Investigation Team for MH370, 8 March 2015, Factual Information MH370/01/15
The Factual Information was updated in 2018 by the Safety Investigation Report MH370/01/2018 which added new content but did not include all of the previous data.