The US National Transportation Safety Board (NTSB) has found that a combination of mechanical defects and the captain's failure to monitor the speed brakes resulted in a runway overrun of an American Airlines Boeing 757-200 in Jackson Hole, Wyoming, in December 2010.
The aircraft stopped 222m (730ft) beyond the threshold of the 6,500ft runway in deep snow after the brakes and thrust reversers failed to deploy. None of the 185 passengers and crew onboard were injured.
The overrun was caused by the confluence of two separate mechanical issues and the captain's failure to follow company procedure to confirm that the brakes had deployed and then manually deploy them when they had not, according to the NTSB report that was released on 5 June.
The brakes did not deploy due to an assembly defect in their no-back clutch mechanism while the thrust reversers were prevented from deploying by a rare mechanical and hydraulic interaction that occurred at the moment when the first officer attempted to deploy them.
The captain, who was the monitoring pilot during landing, mistakenly stated that the brakes had deployed without observing whether they had actually deployed. He then took the controls from the first officer when the thrust reversers failed and managed to deploy them after 18 seconds.
The NTSB found that if the captain had manually deployed the brakes the aircraft could have stopped about 4,500ft down the runway without the thrust reversers.
The board recommends that air carriers include training of situations where the brakes do not deploy for pilots, new air transport aircraft include an unique aural alert when the brakes do not deploy, and Boeing provides guidance to pilots when an unintended thrust reverser lockout occurs, based on the results of its investigation.
American did not comment on the findings.