A sophisticated flight-control system that relies on electronic instruments and computers came under growing scrutiny Thursday as investigators tried to unravel the mysterious crash of an Air France Airbus 330 into the Atlantic.
A series of messages sent automatically by the jet moments before it plunged into the ocean late Sunday with 228 passengers and crew members aboard has raised speculation that the crash might have involved a malfunction of the automated system that flies the plane most of the time.
One of the messages reported that one of the plane's navigational control units had failed and that, almost simultaneously, the autopilot system had disengaged.
The sequence of events forced the crew of Flight 447 to fly the jet manually, a difficult task on an Airbus traveling at high altitude near its maximum speed, aviation experts said. Any significant change in airspeed could have caused the plane to lose lift or stability, both potentially deadly conditions.
Meanwhile, new analysis of the weather in the vicinity at the time of the crash appears to cast doubt on earlier reports that the plane encountered severe thunderstorms, lightning and wind gusts. Though there were storms, they were almost certainly less intense than those sometimes encountered above the United States, and lightning was at least 150 miles away, said Greg Forbes, severe-weather expert for the Weather Channel.
Forbes said an examination of weather data for Sunday, including satellite images, indicated updrafts of perhaps 20 mph, far from the initial reports of 100 mph.
"I wouldn't expect it to be enough to break apart the plane," Forbes said.
Though experts generally agreed Thursday that weather alone did not explain the crash, USC aviation safety expert Michael Barr said the investigation was still wide open.
"You can never disregard any possibility until you can prove what happened," Barr said. "The key here is to determine what the crew could have done after the initial event. Or was there nothing they could have done and they were just along for the ride?"
Air France executives said the plane had sent out a series of messages indicating technical failures, confirming news reports in Brazil and data that U.S. aviation experts had already gained access to.
A series of serious electronic breakdowns occurred on the Airbus over a four-minute period before the jet plunged into the sea, said Robert Ditchey, an aeronautical engineer, pilot and former airline executive.
