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NTSB: Auto speed brake mechanism anomaly noted in Jackson Hole runway excursion incident
12 January 2011

The NTSB issued a second investigation update regarding the runway overrun of a Boeing 757 in Jackson Hole, Wyoming.

At about 11:38 am MT onDecember 29, American Airlines flight AA2253, a Boeing 757-200 (N668AA) inbound from Chicago O’Hare International Airport, ran off the end of runway 19 in snowy conditions while landing at Jackson Hole Airport. No injuries were reported among the 181 passengers and crew on board.

Instrument Flight Rules (IFR) weather conditions prevailed around the time of the incident with a ceiling of 400 feet, light snow and visibility of 1 mile. Winds were 10 knots from 240 degrees.

The NTSB did not find any discrepancies  in the air/ground, autobrake, and thrust reverser systems. Examination of the auto speed brake mechanism in the cockpit pedestal found that the linear actuator aft attachment was improperly installed and was missing a bushing. This loose connection allowed the cam to be rotated slightly relative to the switch, which could cause the switch roller and the notch in the cam to not always align. System operation with this condition present is being investigated.

The flight data recorder readout revealed the following factual information:

  • The FDR download contains the last 43.9 hours of data, more than the required 25 hours, and includes all of the incident flight.
  • The recorded speed brake handle position indicates that the speed brakes were manually extended by the flight crew during the approach after which the handle was left in the armed position until landing. The FDR records only the speed brake handle position and not the individual speed brake (spoiler) panel positions.
  • The FDR data indicate that the aircraft touched down at approximately 132 knots.
  • At touchdown, the air/ground parameter changes to “ground” for approximately one second and then switches to “air” for approximately ½ second before changing back to “ground” for the remainder of the recording.
  • During the time period when the air/ground parameter switched back to “air,” the speed brake handle position momentarily moved toward the down position and then returned to the armed position where it stayed for the remainder of the recording.
  • Thrust Reverser (T/R) discrete parameters indicate that the T/Rs moved into the in-transit position during the ½ second that the air/ground logic parameter indicated “air.”
  • The T/Rs remained in the in-transit position for approximately 10 seconds before transitioning to the stowed position for one second. The T/Rs then moved back to the in-transit position for an additional 6 seconds before becoming deployed.
  • The T/R discrete parameters indicate that approximately 18 seconds elapsed from the time the T/Rs began moving until they were fully deployed.

The investigation is continuing.