A TAM Airbus A330-200 landing at London Heathrow Airport
Photo: Adrian Pingstone
by Clive Irving
Last night the National Transportation Safety Board revealed that within the last five weeks two Airbus A330 airliners have had critical episodes involving speed sensors--the same kind of emergency that is at the heart of the investigation into the loss of Air France Flight 447.
The first episode involved a TAM airlines flight from Miami to Sao Paulo, Brazil on May 21. The language of the NTSB notice describing this is unusually stark:
[The airplane] "experienced a loss of primary speed and altitude information while in cruise flight. Initial reports indicate that the flight crew noted an abrupt drop in indicated outside air temperature, followed by the loss of the Air Data Reference System and disconnections of the autopilot and autothrust, along with the loss of speed and altitude information. The flight crew used backup instruments and primary data was restored in about 5 minutes. The flight landed with no further incident and there were no injuries or damage."
The second episode is more sketchily reported but involves an American carrier, Northwest Airlines, and a flight between Hong Kong and Tokyo on June 23. All the NTSB says about this is that it was "another possibly similar incident" and that the Board is now collecting all the data recorded by the airplane.
What is striking about the account of the TAM incident is that the A330's autopilot disconnected.
We know from the data sent from the doomed Air France flight before it disappeared that it, too, had a similar sequence in which, basically, the main computers shut down and gave up trying to fly the airplane. From the new TAM episode it seems that the sudden demands made of the flight crew to regain control were intense. The fact that it took a whole five minutes for them to do so is a good measure of its seriousness.
Add that scenario to the known course of Flight 447 through extremely violent turbulence at night in a storm that towered to 50,000 feet or more in its flight path which was at 35,000 feet and you see a very serious combination of threats. We don't know yet the route of the TAM flight from Miami to Brazil, whether it passed through the similar tropical storm zone and whether the episode happened in daylight or at night. What does seem clear is that the TAM crew (and now also the Northwest crew) were able to deal with a sudden emergency with great skill.
These failures are all attributable to sensors called pitot tubes made by the French company Thales that weigh about one pound each and are attached to the outside of the airplane. Pitot tubes on the A330 are being replaced because they are prone to ice at cruise altitude and then give false readings. The NTSB notice posted last night is simply an "advisory" and carries no mandatory authority.
Further reading:
* The Fate of Air France Flight 447 (Daily Traveler on CNT)
* What is a pitot tube? (Scientific American)
* National Transportation Safety Board Web Site
* On the Fly: Barbara Peterson on the airline industry
Read Clive Irving's dispatches on Flight 447 in The Daily Beast:
* Picking up the Pieces from a Midair Explosion (June 14)
* The Myth of the Black Box (June 7)
* The Secrets of Flight 447 (June 6)
* Who Was Flying Flight 447? (June 5)
* Last Words of Flight 447: From a Robot (June 3)
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