Computers Probed in Crash Doomed Air France Jet Suffered Cascading System Failure, In
Air investigators, running out of time to find the "black boxes" with key information on the crash of Air France Flight 447, suspect a rapid chain of computer and equipment malfunctions stripped the crew of automation today's pilots typically rely on to control a big jetliner.
An international team of experts is building a scenario in which it believes a cascade of system failures, seemingly beginning with malfunctioning airspeed sensors, rapidly progressed to what appeared to be sweeping computer outages, according to people familiar with the probe. The Airbus A330, en route from Rio de Janeiro to Paris, crashed into the Atlantic Ocean during a storm 26 days ago, killing all 228 aboard.
Based on an analysis of the sketchy information from automatic maintenance messages sent by the aircraft, these people said, the plane bucked through heavy turbulence created by a thunderstorm without the full protection of its flight-control systems -- safeguards that experts say pilots now often take for granted.
Relying on backup instruments, the Air France pilots apparently struggled to restart flight-management computers even as their plane may have begun breaking up from excessive speed, according to theories developed by investigators.
The investigators stress it is too early to pinpoint specific causes. But whatever the eventual findings, the crash already is prompting questions about how thoroughly aviators are trained to cope with widespread computer glitches midflight.
If such emergencies do occur on today's increasingly automated jetliners, many industry safety experts wonder how proficient the average crew may be in trying to rely on less-sophisticated backup systems.
"The difficulty is, they're rare enough that pilots can be unprepared, but likely enough to pose a real threat," according to Bill Voss, president of the Flight Safety Foundation, an industry-supported group based in Alexandria, Va. "We need to examine how to deal with automation anomalies."
Unlike jetliners built in previous decades -- which required pilots to frequently manipulate controls and often manually fly the planes for long stretches -- newer computer-centric aircraft such as the A330 and Boeing's 777 are designed to operate almost entirely on automated systems. From choosing engine settings and routes to smoothing out the ride during turbulence and landing in low visibility, pilots essentially monitor instruments and seldom interfere with computerized commands. So when those electronic brains begin to act weirdly at 35,000 feet, the latest crop of aviators may be less comfortable stepping in and grabbing control of the airplane.
Airlines typically use simulators to train cockpit crews for such events, but a pilot may only hone skills to deal with major computer problems every few years. Pilots hardly ever experience multiple computer failures in real-world conditions.
Crews commanding a flotilla of specially-equipped vessels are still trolling an area with a radius of at least 50 miles for the black boxes -- the digital recorders containing detailed flight data and cockpit conversations from the flight. The sea floor beneath where debris was found floating is mountainous and up to 15,000 feet deep. The recorders are designed to have enough battery power to last for at least 30 days. That deadline runs out Wednesday, though investigators and safety experts believe that signals may last for at least a couple more weeks.
Because the A330 is one of the most widely used planes in commercial aviation, crash sleuths "aren't likely to easily stick with an undetermined cause," according to John Cox, a former Airbus pilot who now works as an industry consultant. Instead, investigators "will exhaust every possibility" to pinpoint probable reasons and contributing factors, Mr. Cox said, even without the black boxes, though they may have to be cautious about a definitive assessment.
In place of that data, they would use computer simulations to try to lay out the possible sequence of events, and then work backwards, eliminating as many potential causes as possible.
A progress report from French officials leading the probe could come as early as next week. At this point, the bulk of the information made public about the Air France tragedy deals with suspected problems with external speed sensors, or so-called pitot tubes, which have a history of icing up and malfunctioning on different Airbus models.
On Thursday, U.S. investigators disclosed two recent incidents in which they believe Airbus A330 jets suffered air-speed sensor malfunctions that led to more sweeping system failures. Both of those planes landed safely.
A Northwest Airlines A330 flying from Hong Kong to Tokyo earlier this week, for example, ran into a situation which investigators believe may be a similar to what took place on the flight deck of the Air France jet.
The Northwest crew reported entering a storm in daylight and running into turbulence; in less than a minute their primary and standby airspeed indicators showed the plane had slowed dramatically. Other systems that automatically maintain speed and altitude also disengaged. Things didn't return to normal for three minutes as the captain flew the aircraft out of the rain, according to information gathered by U.S. safety officials.
The scene inside Air France Flight 447 may have been more ominous from the beginning. The crew was flying at night and the storm they tried to traverse may have been more violent.
After the initial speed warnings, the Air France pilots are believed to have quickly lost the autopilot and automated throttle-controls, which are designed to instantly disengage when speed readings are suspect. Soon after, according to people familiar with the investigation, cockpit instruments showed a series of warnings about various other equipment failures and the crew apparently shut down or tried to reboot their primary and secondary computer systems.
It's not clear what happened next. But the pilots, perhaps distracted by wildly fluctuating airspeed indications, along with the cacophony of other cockpit warnings, could have allowed the jetliner to gain excessive speed that possibly tore off sections of the plane.
The aircraft could have accelerated and run into danger because faulty instruments convinced the Air France crew the twin-engine jet was traveling so slowly that it was close to stalling. That may have prompted them to rev up the engines or point the nose down to go faster.
One difficult question is whether all three air-speed sensors located on the lower curve of A330's nose -- including a backup device -- failed. If so, investigators are trying to understand whether the pilots followed procedures that call for maintaining engine power and whether they took other steps to ride out the emergency. Planes can -- and occasionally do -- fly safely without pitot probes functioning properly. That's why industry and government investigators believe some other important factor, which hasn't been identified yet, likely contributed to the crash.
Airlines are likely to pay more attention to helping pilots better understand the ripple effect that can occur when computerized flight controls, altitude indicators and other systems go haywire. There are detailed check lists for each chain of events, but to save on training time and cost, typically airlines limit simulator time for pilots to experience the full range of things that can go wrong.
"Such issues are talked about regularly during training," according to John Goglia, a former member of the National Transportation Safety Board, but "pilots only occasionally have the chance to practice" reverting to backup cockpit instruments and flying without the usual computerized systems.