Air France 447: New Questions About Instruments, Composite Tail

• Airbus
• NTSB
• aviation
• plane crashes
• aircraft

Last night the U.S. National Transportation Safety Board (NTSB) announced it had been investigating primary flight instrument failures aboard two separate A330s since late May. If those same instruments failed aboard AF447 when it encountered severe thunderstorms, the flight computers and the crew may have been able to inadvertently fly the aircraft beyond its structural design limits, triggering an in-flight breakup.

That hypothesis gained credence when the aircraft's tail, or vertical stabilizer, was found floating in the water June 8. Without black box data, what exactly caused the tail to come off may never be known. However, there have been other crashes involving all-composite tails. On November 12, 2001, the tail came off an American Airlines Airbus A300 as it flew through wake turbulence on climb-out from New York's JFK, killing 265. The NTSB blamed that crash on a combination of overly aggressive rudder inputs by the pilot flying, the airline's training program and "characteristics of the A300-600 rudder system." On May 12, 1997, another A300 experienced an in-flight upset, a series of rolls and stalls, severe rudder deflections and high structural loading on an approach to Miami. The aircraft landed safely and intact and was cleared for flight following an inspection using accepted techniques, but Airbus engineers requested a more thorough inspection of the composite tail. When that inspection occurred in 2002, the composite material had delaminated so severely that the $1.9 million tail was scrapped.

Both Boeing and Airbus are betting their futures on new composite aircraft, the 787 in Boeing's case and the A350 for Airbus. Composites have weight and structural strength advantages over aircraft aluminum, but aviation officials say that much remains to be learned about how they degrade over time. Earlier this month the FAA issued a draft Advisory Circular aimed at changing the certification rules for composite aircraft. In the document the FAA notes that the "nature of composites can make the determination of critical structural failure loads, modes and locations difficult." On Tuesday Boeing announced another in a series of delays for the 787 program as engineers worked to resolve structural concerns, widely believed to involve delamination where wing meets the body, following load testing.

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