by Chris Sorensen on August 24, 2011
With low clouds and a fine mist hanging in the morning air, the pilots of Turkish Airlines Flight 1951 anticipated a routine approach to Amsterdam’s busy Schiphol Airport on Feb. 25, 2009. But instead of touching down gently on the runway, the white and red Boeing 737 dropped out of the sky and slammed into a muddy field just short of the airport, smashing into three pieces. Nine people died, including all three pilots. Another 84 were injured.
Investigators attributed the crash to a faulty radio altimeter, aggravated by pilot errors and oversights. Radio altimeters use radio waves to measure a plane’s altitude—a key piece of equipment, which is why a 737 is equipped with two of them. But what nobody in the cockpit of Flight 1951 realized was that the malfunctioning altimeter happened to control the 737’s auto-thrust systems. So while the co-pilot was busy monitoring the autopilot (which used data from a different altimeter), and Capt. Hasan Tahsin Arisan was watching the co-pilot as part of a training exercise, and a third “safety” officer was supposed to be watching everyone to make sure nothing got missed, the auto-thrust erroneously engaged its “retard” mode, thinking it was just above the runway. The throttles were cut and the plane’s nose pitched up, causing the plane to drift into an aerodynamic stall. The flight crew tried to recover by returning the throttles to full power, but their initial efforts were thwarted by the confused auto-thrust system, which they forgot to disengage. There was no time for a second try.
Statistically speaking, modern avionics have made flying safer than ever. But the crash of Flight 1951 is just one of several recent, high-profile reminders that minor problems can quickly snowball into horrific disasters when pilots don’t understand the increasingly complex systems in the cockpit, or don’t use them properly. The point was hammered home later that year when Air France Flight 447 stalled at nearly 38,000 feet and ended up crashing into the Atlantic, killing all 228 on board. Investigators recently released transcripts from the Airbus A330’s cockpit voice recorder. It reveals a flight crew gripped by confusion as they tried to diagnose and respond to what should have been a manageable mid-air emergency, but instead resulted in a terrifying 3½-minute plunge in total darkness. “I don’t have control of the airplane anymore,” the co-pilot at the controls said at one point. “Now I don’t have control of the airplane at all.”
Despite being responsible for the lion’s share of passenger deaths over the past decade, it’s only recently that the industry has begun to treat so-called “loss-of-control” accidents as a serious issue. Sunjoo Advani, an expert in flight simulation and the president of a Netherlands-based simulation and engineering consulting firm, says he received puzzled looks when, back in 2007, he suggested that Britain’s Royal Aeronautical Society (RAeS), an influential safety group, hold a conference on the issue. Not anymore. Advani has spent the past two years coordinating the International Committee for Aviation Training in Extended Envelopes, or ICATEE, a panel of experts asked by the RAeS to look into stalls and other loss-of-control accidents and find ways to prevent them. “Many of these accidents are recoverable,” he says. “They simply shouldn’t have happened. In many incidents, the airplane has gone into a stall and every automated safety procedure kicked in, but the pilots failed to recognize the situation and failed to recover.
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