Monday, June 8, 2009

Uncompleted Pitot Tube Modification is Only Part of Air France 447 Crash Story

At 35,000 feet, the Airbus A330, the Air France 447 plane that crashed, is only about 25 knots between cruise speed and aerodynamic stall. Thus, if wind shear and turbulence are sufficiently violent, the aircraft can stall and the air data computers will take the autopilot offline because the equipment senses an anomaly. The airplane will be thrown around like a feather and composite structures will fail because they have never been tested to ultimate load. That stall can also result in the aircraft becoming unrecoverable while it breaks up on its way to lower altitudes.

With all the computing power in an A330, sources outside of the aircraft should be used to supplement radar so that the computer can determine when it’s time to turn back.

It’s also time for certifying authorities to rethink how to test composite aircraft structures. It is no surprise that that the big thing found floating in the Atlantic Ocean was the composite vertical stabilizer separated from the rest of the airplane. Speculation is that the Pitot Tubes, which were unmodified as recommended for better ice resistance, permitted erroneous speed readings. I believe this is possible but unlikely. However, if the risk was so high, the modification should have been required before further flight was permissible.

Why isn’t anyone talking about the tail fuel tank modification that was designed to prevent explosions caused by lightning? Did the airline comply with that directive? There are a lot of questions…too few answers.

Arthur Alan Wolk
June 8, 2009

Watch Wolk discuss the issue on MSNBC