NTSB: Combined events caused Jackson runway mishap
CHEYENNE, Wyo. (AP) — A combination of mechanical problems and inadequate monitoring by the captain likely caused an American Airlines passenger jet to go off the end of the runway into deep snow at the Jackson Hole Airport, the National Transportation Safety Board said Tuesday.
The Boeing 757-200 overshot the runway by 730 feet after it landed Dec. 29, 2010. The plane sustained minor damage but none of the 185 passengers and crew on the flight from Chicago was hurt.
As a result of the mishap, NTSB staff recommended additional training for pilots and installing alarms that go off when plane-slowing devices known as speed brakes don't automatically deploy upon landing.
Jackson Hole Airport, in the southern end of Grand Teton National Park, is a notoriously difficult place to land, especially for larger jets. Mountain ranges crowd the relatively short runways at the only commercial airport located inside a U.S. national park.
The airport is Wyoming's busiest by virtue of handling a good chunk of Yellowstone-Grand Teton tourist traffic.
The board determined that a combination of unusual events caused the incident.
First, the plane's thrust reversers, which divert jet thrust forward to slow the plane down, did not engage after the plane touched down. No mechanical defect turned up in the plane's thrust reversers.
As the plane continued to roll down the runway, a manufacturing defect in a clutch that causes the plane's speed brakes to engage kept them from engaging automatically. Speed brakes are wing flaps that create air drag and downward force on the plane's wheels.
The plane was under the direct control of the first officer, not the captain, whose role was to monitor the first officer.
Even so, the captain intervened and tried to get the thrust reversers to engage. In doing so he failed to notice that the speed brakes hadn't deployed automatically and missed an opportunity to engage the speed brakes manually, according to the NTSB staff.
"If they had deployed their speed brakes, this plane would have stopped on the runway," Katherine Wilson, a human performance investigator for the NTSB, said at a hearing in Washington, D.C., that was webcast live.
The speed brakes on the same plane failed to deploy again three months later upon landing in San Francisco. That runway is about 4,000 feet longer than the one in Jackson Hole, however, and the plane didn't get into trouble.
Increasing reliability of aircraft equipment in recent years means problems are more likely to take pilots and crew by surprise, Wilson noted.
"Pilots become complacent and are less likely to monitor those systems," she said.
The pilot and first officer also could have followed a procedure to engage the thrust reversers. The NTSB recommended training and other guidance for pilots to address situations when speed brakes and thrust reversers don't work properly.
The captain and first officer have completed a voluntary Federal Aviation Administration accident prevention program and have returned to duty, American Airlines spokeswoman Andrea Huguely said.
"Even though incidents like this are extremely rare, all of our employees — from our pilots to our licensed mechanics to our gate attendants — we are professionals and we are committed to the safety of our customers and co-workers," she said.
