As media speculation centers on lightning and air turbulence as possible causes of the disappearance of an Air France flight from Rio de Janeiro to Paris, many aviation analysts are puzzled by the circumstances of the missing plane.
The plane, a twin-engine Airbus A330-200, took off from Galeão Airport at 7:30 p.m. local time with 228 people on board. It was last heard from three hours later when it radioed to say it would enter Senegalese air space within the hour, according to a statement from Aeronautica, which is in charge of Brazilian air space.
At that point, the plane was flying "normally" at 35,000 feet. About a half hour later, Air France says the plane sent out an automatic message reporting "a loss of pressure and failures of the electrical system." Then silence.
The Airbus A330 has an excellent safety record – in fact, it's never been involved in a fatal commercial crash. One reason is the way it's designed: It has multiple redundancies that kick in if there's an electrical or any other kind of failure. And with authorities in France ruling out terrorism or a hijacking, many analysts say they are baffled by the plane's disappearance.
"These planes go through turbulence all the time and they do get hit by lightning – while it may startle the passengers it's not something that should create a problem that would cause a jet to stop flying. They're designed so things can fail and the plane can continue to fly without any problems," says Clint Oster, an aviation analyst at Indiana University in Bloomington.
"It's not adding up right now. There clearly has to be something else going on – some unusual circumstance we don't know yet."
What Airbus's backups do
The Airbus A330 is a "fly by wire" jet, which means the flight controls are not moved by pulleys and cables but are electrically controlled and hydraulically activated, according to an A330 pilot who is not authorized to speak to the press. As a result, it is more difficult to fly when it shifts into an emergency mode.
"I wouldn't want to be in emergency electrical configuration and in severe turbulence, but it is controllable – you can fly," says the pilot. "But if they lost all hydraulics for some reason, again highly, highly unlikely due to the design of the A330, then they would not be able to remain airborne. You can't fly without hydraulics."
The A330 has several backup electrical systems that are supposed to run the hydraulics. Those backups are also designed to ensure there's still some kind of radio contact that could be used to send out a Mayday call. The fact that the plane was able to send out an automatic message indicating the electrical failure has some analysts puzzled as to why there was no communication from the pilots themselves.
"Because of the fact that we had that report from the airplane itself, it indicates the plane was intact then. It also indicates there was two-way communication going on and the pilots would have had communications at least to their operations center, if not Air Traffic Control," says William Voss, president of the Flight Safety Foundation in Alexandria, Va.
"All of these things just increase the level of mystery here as to why more information wasn't communicated," he says.
The A330 pilot says that the Air France pilots may have been "task saturated," that is, too busy trying to fly the plane to put out a Mayday call, but she adds that that's unlikely. She says it's also possible the pilots did put out Mayday call but it was on a frequency that wasn't working due to the electrical problems or no other flights in the air heard it.
But it's unlikely that no other planes were in the vicinity at the time, she adds.
An electrical failure? Too soon to tell
Flight Safety Foundation's Mr. Voss says it's too early to conclude that there was a catastrophic electrical failure, despite fears expressed by some at Air France that the plane may have been hit with lightning.
"When they have a sophisticated aircraft that relies heavily on electronics like they do in the A330, they [the designers] take that into account," says Voss. "There are things that they do in the aircraft to make sure that if it does get hit, the lightning strike gets conducted around the skin [of the plane] as opposed to through the cabin or the electronics."
Other aviation analysts note that commercial planes have to be certified by the FAA that they can handle a lightning strike.
"Part of the certification requires that whatever happens, it can't result in a catastrophic failure or a loss of the aircraft," says Richard Golaszewski, executive vice president of an aviation consulting firm in Jenkintown, Pa. "They have to show that it's extremely unlikely, and the general rule for 'extremely unlikely' is ten to the minus nine – which is one in a billion." [Editor's note: The original version included an inaccurate calculation and has been corrected.]
Given the few available details about the Air France plane's situation, the commercial A330 pilot says she is surprised by the French authorities's ruling out terrorism or a hijacking.
"Given the fact that nobody heard anything from the pilots [and] they don't know much about the plane – how can they possibly rule all of that out?" she asks.
• Correspondent Andrew Downie contributed to this report from Brazil.