JAC Investigation
An undetected maintenance error, compounded by pilot mistakes, likely caused an American Airlines Boeing 757 to roll off the end of a Wyoming runway in snowy conditions last month, according to people familiar with the details.
Federal safety officials, these people said, are now examining whether the same maintenance lapse discovered after the Dec. 29 incidentwhich didn't injure any of the 181 people aboardmay affect some of the carrier's other planes.
Arriving at Jackson Hole, Wyo., amid light snow and low visibility, the twin-engine Boeing 757 slid more than 600 feet off the end of the strip into hard-packed snow.
Investigators are examining why the pilots didn't promptly recognize certain automation failures that allowed the jetliner to keep barreling down the runway. The probe is examining whether the maintenance lapse caused those failures. Investigators are also examining why the pilots didn't manually deploy certain panels on the wings designed to help slow the aircraft.
A spokeswoman for the AMR Corp. unit and officials at the Federal Aviation Administration declined to comment.
The incident has attracted widespread attention because earlier this month, the National Transportation Safety Board determined that American violated long-established "standards of conduct" by improperly downloading information, for its own use, from the plane's flight-data recorder before turning the device over to the government. As a result, the board took the unusual step of barring American from further participation in the federal probe.
In an update of its preliminary findings released Wednesday, the safety board disclosed that the runway incident followed problems experienced by two separate systems designed to help decelerate the jetliner.
Panels on top of the wings, known as spoilers, failed to automatically pop up and help slow the aircraft, according to investigators. The safety board said that a portion of the linkage to an electrical switch needed to automatically activate the spoilers on the ground "was improperly installed" during earlier maintenance procedures. Investigators didn't indicate when mechanics made the alleged mistake.
Contrary to American's checklists and safety procedures, the cockpit crew apparently failed to try to manually deploy the spoilers in Jackson Hole, according to people familiar with the details.
In addition, the safety board said separate devices at the rear of the engines also designed to help the plane come to stopcalled thrust reverserstook too long to deploy. "Approximately 18 seconds elapsed" from the time the plane's landing gears touched the runway "until [reversers] were fully deployed," according to the update. Typically, the devices should kick in and start redirecting engine thrust in a matter of seconds. They are controlled by the crew.
The plane's cockpit-voice recorder, however, indicates that the pilots commanded the reversers to deploy as soon as the plane touched down, according to people familiar with the details. One angle the safety board is pursuing is whether the earlier maintenance errorpotentially binding or restricting the operation of various controls in the cockpitcould have caused the delayed response from the reversers.
To help answer that question, these people said, the FAA has told American to inspect a portion of its Boeing 757 fleet for similar maintenance lapses.
According to the board's latest findings, the 18-year old jetliner experienced "no significant issues with any of these systems" prior to the incident, and all required maintenance items were up to date prior to last month's flight from Chicago to Jackson Hole.
Almost precisely a year earlier, An American Airlines Boeing 737 ran off the end of a wet runway at Kingston, Jamaica, after touching far down the strip. Unable to stop with almost half the 8,900-foot runway behind it, the plane barreled off the strip at more than 60 miles per hour and broke apart. There were no fatalities.
In that event, Jamaican and U.S. investigators have concluded that the plane's brakes, reversers and other systems basically operated as designed, but standing water on portions of the runway likely made it difficult for the pilots to stop in time.