WASHINGTON — Speeding down a snowy Wyoming runway after touchdown at more than 100 miles an hour, devices on the American Airlines jetliner that use engine power to slow down malfunctioned.
As the pilots struggled with that, they failed to notice an even more critical failure on the Boeing 757: panels on the wings that are essential for braking hadn’t deployed.
The Dec. 29, 2010, incident, in which a plane carrying 185 people skidded off the runway, highlights how today’s automated, normally reliable aircraft can breed complacency in pilots, the National Transportation Safety Board concluded in a hearing in Washington Tuesday.
“This incident demonstrates that experienced pilots can become distracted during unusual events,” Katherine Wilson, an NTSB investigator who specializes in human performance, said.
Blame for the accident was divided between the malfunctions of the braking systems and the American Airlines captain’s failure to notice that the panels known as speedbrakes had malfunctioned, the safety board found in a unanimous vote.
Brakes are 60 percent less effective without the speedbrakes, which push a plane’s wheels into the pavement, Wilson said. Even with the balky thrust reverser, the plane would have stopped by the end of the runway had the pilots manually switched on the speedbrakes, she said.
None of the 179 passengers and 6 crew members aboard the aircraft were injured when it slid off the 6,300-foot runway and came to rest 730 feet away in a snow-covered field, according to the NTSB. The flight was from Chicago’s O’Hare International Airport to Jackson Hole Airport.
“The airplane felt like a sled,” co-pilot Todd Brann told investigators, according to an NTSB report.
A simultaneous series of events aboard the jetliner prevented its braking systems from functioning, the investigation found. Because the plane’s computers momentarily concluded the aircraft had lifted off again after touchdown, it blocked the thrust reverser from working, the investigation concluded.
The design of the reversers prevented the pilots from reactivating them immediately, an anomaly none of the pilots interviewed in the investigation had heard of.
It wasn’t until March 31, 2011, when the same jetliner landed in San Francisco and the speedbrakes malfunctioned again, that investigators realized that the unit on that aircraft contained a manufacturing error, according to the safety board’s findings.
American’s pilots are required to check after landing to ensure the speedbrakes are working. Captain Timothy Kalcevic could be heard on the plane’s crash-proof cockpit recorder saying that they were “deployed,” Wilson said.
In fact, they hadn’t automatically switched on, the safety board found. Wilson attributed Kalcevic’s comment to the fact that he expected them to work as they had in the past.
As jetliners have become more computer-driven, pilots spend more time monitoring autopilots and other systems, NTSB Chairman Debbie Hersman said in an interview after the hearing.
“That monitoring is no less important than the hand flying they once did, and failing to be attentive to the monitoring can be just as catastrophic,” Hersman said.
Pilots need more time in simulators to practice in increasingly complex cockpits, Rory Kay, a safety consultant and airline pilot who authored a report last year on the hazards of increased automation, said in a phone interview.
“Quality training is the best solution to this,” Kay said.
The NTSB voted to recommend that all airlines develop new training on the importance of monitoring speedbrakes. A review of incident reports by the safety board found 11 cases in which the speedbrakes activated and then deactivated on their own.
The board also recommended that a warning horn be installed on jetliners to alert pilots if the speedbrakes are not working. The board doesn’t have authority to implement changes on its own.
“We’re satisfied that the NTSB took a thoughtful approach in the investigation and assessment of this incident,” Gregg Overman, a spokesman for the Allied Pilots Association, the union representing American’s flight crews, said in an interview.
American has already added training on speedbrakes, Ed Martelle, a spokesman for the carrier, said in an interview.
The U.S. Federal Aviation Administration, which regulates airlines, will review the recommendations, the agency said in an e-mail statement.
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