As the search for flight MH370 persists, Europe’s aviation safety authority has, ironically, been assessing the costs of reinforcing the underwater locator features on aircraft and their flight recorders.
This assessment is part of a proposal drawn up after the similar loss of Air France flight AF447 aimed at avoiding frustrating and expensive efforts to trace aircraft missing over oceans.
European Aviation Safety Agency regulators are seeking to raise, from 30 days to 90 days, the minimum transmission duration of acoustic 37.5kHz underwater locator beacons installed on the cockpit-voice and flight-data recorders.
The measures also call for installation of 8.8kHz beacons on aircraft performing long-range overwater flights.
Both were put forwards as part of a broader package to make flight recorders more robust and easier to locate.
EASA’s comment period for the proposals closed on 20 March as search and rescue organisations struggled to cover vast areas of remote oceanic territory in the hunt for Malaysia Airlines’ missing Boeing 777.
The proposal illustrates the expense and limitations of such search operations. Use of a remotely-operated vehicle, says EASA, can run up daily costs of $150,000 to $200,000 – and such a vehicle might only cover 5km2 in 24h.
“The cost of underwater search operations is a function of their duration,” it adds. “Cost is critical when the safety investigation authority cannot dedicate large financial means to the underwater search operations.”
EASA estimates the long-term economic cost, over 10 years, at between €5 million and €50 million.
Fitting the European aircraft fleet with 90-day beacons, by the beginning of 2020, would cost around €12 million.
But even with an extended transmission time the 37.5kHz signal poses serious limitations in deep water. While a transmission range of 2,900m is theoretically possible, EASA suggests 1,500m is a more realistic figure, based on previous search operations.
Deeper water rapidly shrinks the detection radius at the surface, and severely limits the area a vessel can cover in a day. Detecting a beacon which has sunk to extreme depths requires several kilometres of cable to lower a towed pinger locator to within range.
EASA points out that, when the towing vessel reverses direction at the end of each search track, such a long cable “takes hours” to be correctly realigned. The profile of the sea floor also complicates the task of maintaining the detector at the ideal distance.
Installing a locator beacon on the aircraft which operates at the lower 8.8kHz frequency would substantially increase detection range, to around 10,700m. This would mean that the depth of the ocean would have much less impact on the area that could be covered daily. EASA calculates that a 14-day search could cover almost 30,000km2 even with an ocean depth of 6,000m.
Retrofitting the 8.8kHz beacon on the European fleet, it adds, would cost around €9.8 million by the implementation date of 2019. The missing Malaysia Airlines 777, even if it had been European-registered, was built in 2002 – the proposed retrofit would apply to aircraft from 2005.
Investigators took 692 days to recover both flight recorders of AF447, exceeded only by the 840-day hunt for the recorders of a South African Airways Boeing 747 lost in 1987. The flight-data recorder of the 747 was never found.
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