A TAM Airbus A330-200 landing at London Heathrow Airport.
Photo: Adrian Pingstone
by Clive Irving
How many Airbus A330s are flying throughout the world with a key piece of equipment that can jeopardize safety? This question became more urgent with the release last night of a statement by the National Transportation Safety Board revealing two recent incidents in which pilots had to regain control after automated controls failed.
Moreover, these incidents involve failure of speed sensors--the same kind of failure that is at the heart of the investigation into the loss of Air France flight 447.
Last night's notice from the NTSB disclosed that a TAM airlines flight from Miami to Sao Paulo, Brazil, on May 21 suffered an emergency while at cruise altitude. The A330's flight management system--the master computer that controls the whole airplane--"experienced a loss of primary speed and altitude information" said the notice. "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."
For five minutes the flight crew had to use backup instruments while rebooting the main computer until they regained control. The second episode was this week and it involved an American carrier, Northwest. There was, says the NTSB, "another possibly similar incident" on a flight between Hong Kong and Tokyo on June 23. Both flights landed with no further problems and no injuries or damage.
How the NTSB learned of these incidents shows how piecemeal and haphazard the means are for reporting potentially dangerous situations. A Safety Board spokesman told me today that it was the Brazilian government that informed them of the TAM incident. And it was not the airline that notified the board of the Northwest incident but it was reported to them by "a pilot-oriented internet publication."
There are striking similarities between the TAM and Northwest system failures and what was reported to be happening to Air France flight 447 before it disappeared. We know from data bursts sent from Air France A330 that it, too, suffered a similar sequence of failures in which, essentially, the computers shut down and gave up trying to fly the airplane. Add to that the fact that flight 447's course took it over the South Atlantic directly into the path of a monster storm that created violent turbulence, and that all this occurred at night, and you have a credible scenario for disaster.
The control failures have been attributed to sensors called pitot tubes made by the French company Thales. Air France is replacing pitot tubes on its A330 fleet because they are prone to ice at cruise altitude and then give false readings.
The NTSB is an investigative agency, not a regulatory one. Its advisories like the one issued last night carry no mandatory powers. As the Safety Board spokesman told me, "Only regulatory agencies can order mandatory refits."
So once more, the responsibility lies with the FAA to decide if there is now enough empirical evidence to show that these faulty speed gauges are an immediate threat to air safety, and order A330s grounded until they are fitted with upgraded pitot tubes. As Airbus itself said last week at the Paris Air Show, the A330 is a workhorse in wide use--"one takes off every minute" according to a company executive. From the urgent way in which the Safety Board made known these new episodes it seems that they are far from sanguine about the risks.
* 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)