Canadian and US safety boards are recommending changes to cockpit voice and flight data recorders (CVRs and FDRs) to prevent power interruptions which have complicated recent accident investigations.
Canadian investigators say their efforts to determine the cause of last September's Swissair Boeing MD-11 crash have been compromised by missing data. The CVR and FDR on Flight 111 stopped almost 6min before the aircraft hit the water.
Canada's Transportation Safety Board and the US National Transportation Safety Board (NTSB) have both recommended that CVRs be provided with independent backup power sources and that CVRs and FDRs be driven by different electrical buses.
Investigators say the Swissair crew may have switched off the bus powering the MD-11's recorders as part of a standard emergency checklist to clear smoke from the cockpit. Boeing plans to connect the two recorders to separate power supplies on the MD-11 as well as to the 737 and 747.
The Canadian and US safety boards also recommend that CVRs be upgraded to solid-state units, with 2h recording capacity. Cock-pit events during repeated attempts by Boston air traffic control to contact Flight 111 about 1h before the crash were recorded over.
The NTSB's specific recommendations are to:
Require retrofit, after 1 January 2005, of all CVRs to a solid-state unit with 2h capacity and an independent power source providing 10min of operation; Require all aircraft manufactured after 1 January, 2003, to be equipped with two combination CVR/FDRs, with 25h data and 2h voice capacity, one to be as close to the cockpit as practicable and provided with backup power, and the other to be as far aft as practicable and powered by a separate bus.The NTSB cites 52 accidents and incidents since 1983 in which recorder information was lost because of power interruptions.
Source: Flight International
