Air France crash: Probe into two other A330 incidents

In the past five weeks, two Airbus A330 planes had computer anomalies that may be similar to the ones now being examined as a possible cause of the crash of Air France Flight 447 in the Atlantic Ocean on June 1.

The National Transportation Safety Board (NTSB) announced Thursday evening that it was investigating two recent incidents "in which airspeed and altitude indications in the cockpits of Airbus A330 aircraft may have malfunctioned."

Just prior to when Flight 447 apparently broke up in-flight, it sent a batch of automated messages that indicated, among other things, inconsistent speed readings. At high altitudes, the plane's speed is measured by sensors called Pitot tubes, which have a history of icing up and sending inconsistent readings. Before the crash, Air France had planned to replace the Pitot tubes on its Airbus A330s and since the accident, it has done so. But Air France and aviation analysts say the Pitot problems alone would probably not have caused a crash.

As a result, investigators are also looking at whether the A330's highly computerized flight control system may have malfunctioned as a result of the inconsistent speed indications. Last week, the Monitor reported on other cases of computer malfunctions on A330s last year that resulted in what pilots call "uncommanded" movements.

Aviation analysts say the NTSB is right to investigate these recent incidents because they appear to have similarities with the Air France crash.

They certainly tie in with various instances of the Airbus A330 making movements the pilot did not command, says Lee Gaillard, an aviation analyst. "So it's certainly very appropriate that they should be looking at them."

The first incident the NTSB is investigating occurred May 21, when a TAM Airlines A330 "experienced a loss of primary speed and altitude information while in cruise flight," according to a release from the NTSB.

"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 TAM flight was on route from Miami to São Paulo, Brazil. It took the flight crew five minutes to regain control of the aircraft, according to the NTSB.

There's less detail about the second incident. The safety board said it "became aware of another possibly similar incident" that occurred on a June 23 Northwest A330 flight between Hong Kong and Tokyo.

In both cases, the planes landed safely and there were no injuries, the NTSB said.