A recent near-fatal incident involving a similar Airbus A330 could provide clues as to the cause of the Air France crash.

Last October, a Qantas A330 plunged 650 feet in a few seconds after a computer malfunction which was possibly triggered by electrical interference.

More than 50 people were injured in the incident which happened suddenly at 37,000 feet over Western Australia.

The air data computer, which is supposed to correct mistakes by the pilot, sent the A330 into a very steep dive. The computer mistakenly thought that the pilot was trying to climb too fast.

In fact the aircraft was level and cruising normally.

The pilot managed to regain control and pull out of the dive but not before all those not strapped in had been thrown around the aircraft.

One theory being investigated is that signals from a nearby military communication station interfered with the air data computer.

Jim Morris, senior solicitor at Stewarts Law, the aviation law firm which is representing 30 people injured in the Qantas incident, said: "Electrical systems on aircraft are designed to withstand lightning strikes. But it appears that the air data inertial reference unit on the A330 is more susceptible than it should be to electro-magnetic interference."