According to investigation results that have remained classified until now, the A320 apparently behaved in an unexpected way during the high-wind landing. The most likely explanation is that because one of the plane's tires had already briefly touched the ground, the flight computer switched from approach mode to ground mode. But when the computer is in ground mode, it does not permit the pilots to turn the ailerons as sharply as they would have done to handle the extreme crosswinds. The computer intervened by limiting the angle of the ailerons, causing the wing tip to suddenly scrape across the runway.
"This sort of behavior on the part of the aircraft wasn't described in any manual," says one pilot critically -- nor is it described today, because Airbus is remaining tight-lipped about the incident until the investigation is complete.
The landing could easily have ended in a disastrous accident. The computer was in control for almost three seconds. It was only through the determined intervention of the pilot, who pulled the plane back up into the air, that the aircraft, traveling at more than 200 kilometers per hour (124 mph), could be prevented at the last minute from crashing.
It is generally undisputed that digital technology on board has helped improve aviation safety. In the vast majority of cases, it helps prevent dangerous situations in the air before they become a problem.
But all of these incidents effectively show how digital equipment can also become a threat. The mysterious breakdowns have triggered a debate in aviation that both airlines and manufacturers would prefer to avoid. How much more high-tech equipment should engineers insert into the cockpit? Does more digital technology automatically result in improved safety? And how much power should flight computers be allowed to have before pilots become disastrously impotent?
The Computer Co-Pilot
Computers have a Janus-faced nature. On the one hand, they help prevent crashes, which is why no one questions their right to exist. Some experts would even like to see more computers in the cockpit. British aviation expert David Learmount, for example, believes that computers could replace one of the pilots in the cockpit one day. "Why do you need two if the computer system is the captain's copilot?" Learmount asks provocatively.
On the other hand, the computers themselves can turn into a safety problem. When the Australian accident investigators took a closer look at the details of the Qantas Flight 72 incident, they discovered that it was by no means an isolated case. Last December, just two months after the drama off the Australian coast, a similar problem occurred on board another Qantas A330. Airbus competitor Boeing is not immune to unexpected computer glitches, either. In 2005, a flight computer caused a Boeing 777 to climb 700 meters for no apparent reason. It happened twice during the flight and caused the jetliner to lose more than a third of its speed, so that it almost stalled.
"Incidents of this nature are a harbinger of what is to come," says Thomas Haueter, the director of aviation safety at the powerful US National Transportation Safety Board (NTSB), which investigates air accidents. He is alluding to the kinds of breakdowns in on-board computers that are difficult to predict. "Lots of people are very concerned that previously unknown problems could arise from the overabundance of computers and software." Haueter wants to make sure that pilots can never lose complete control over their aircraft.
There are about 2,000 computers operating in a modern Airbus A320 short-haul jetliner. They control the air-conditioning system, monitor the engines and check the toilets, but they also help fly the plane.
The days are long gone when a pilot fully understood his aircraft. "We have to make a huge effort so that we don't experience a decline in aviation safety," says Haueter. The manufacturers are well aware of the problems. "They know that automation is the way of the future, but they also know that computers have to be tested more effectively than they have been until now."
The authors of a report released by the US National Academy of Sciences (NAS) describe "several aircraft accidents" in which pilots confused various computer settings. "The software behaved the way it had been programmed to behave, but not the way the pilots expected." The US Federal Aviation Authority (FAA) agrees that the growing computerization of aircraft makes "validation and verification of software more challenging." Programs have become so complex that they can hardly be tested for all eventualities anymore.
"If you were to stack up the technical documentation for an airplane, it would create a mountain of paper three times as tall as the Eiffel Tower," says Marc Diouane, a senior vice president of the American software company PTC.
For a long time, the aviation industry could safely claim that flying had indeed become safer. Year after year, millions of tourists board planes to their vacation destination without hesitation. Even passengers who are afraid to fly now believe that the most dangerous part of flying is driving to the airport.
Statisticians have computed that this saying can be taken literally. The fact that many people switched from flying to driving after the attacks of Sept. 11, 2001 ultimately led to more deaths on the road than in the planes used in the attacks.
"An Unparalleled Success Story"
There is currently less than one accident with fatal consequences for every million takeoffs and landings. Around 1960, at the beginning of the jet age, this figure was still at 11. If aviation were as unsafe today as it was in the 1970s, an airplane would fall from the sky once a week.
Does this mean that all is well in the world of aviation, as we board our summer vacation flights this year? There is no doubt that today's airplanes are so reliable that we tend to forget that we are sitting in an aluminum tube equipped with a full tank of kerosene and traveling at just below the speed of sound. Engine failure, one of the main causes of plane crashes in the past, is a rarity today. The pressurized cabin, hydraulic system and landing gear have become much more reliable. Computers provide advance warning of the threat of ground impact or a collision with another plane. And the guide beams in the landing system direct planes down onto the runway as if they were traveling along a chain of pearls, even in heavy fog.
"When it comes to safety, aviation is an unparalleled success story," says Stefan Levedag, director of the German Aerospace Center (DLR) in Braunschweig in northern Germany. But that could be history now. There were more aviation deaths in the first half of 2009 than since 2002. After the Airbus crashes of Air France over the Atlantic and Yemenia Airways off the Comoros, the number of dead passengers, 499, was about 50 percent higher than the average for the last 10 years.
Judging by the latest accident statistics, which Flight International published last week, a historic turning point has been reached. While the crash rate decreased in every decade since the days of the Wright brothers, it appears to be stagnating for the first time between 2000 and 2010. "Is safety on the slide?" the magazine asked.
A new aviation safety debate has been raging for some time among experts. "How are we supposed to improve the high level of safety even further?" Levedag asks in exasperation. For better or for worse, this is precisely what the aviation industry is condemned to do, as the number of airplanes in the sky grows rapidly and, along with it, the risk of accidents. In a recent study, a European Union advisory panel calls for reducing the accident rate in aviation by an additional 80 percent between now and 2020.
How this goal is to be reached remains unclear. It has already become difficult to compensate for the rise in air traffic with an increase in safety. Some experts already see a trend reversal taking place. The number of minor incidents and near-accidents has risen, says the safety expert for a major airline. The rule of thumb is that for every crash or accident involving personal injury, there are hundreds of accidents involving property damage, as well as minor incidents. "And we have detected a rising trend at this lower level," says the insider.
Experts fear that the possibilities for further increasing safety through improved maintenance systems or state-of-the-art collision warning systems have been exhausted. In addition, new safety hazards are emerging, including a more crowded airspace, ruinous competition and, as a result, poor maintenance and training. Finally, the race to computerize aircraft also creates new risks arising from the complexities of the binary chatter of the thousands of computers on board an aircraft.
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