Investigators at the US National Transportation Safety Board have officially declared the probable cause in the fatal crash of a Colgan Bombardier Q400 was the captain's inappropriate response to a stickshaker activation warning that sent the aircraft into an unrecoverable stall.

The aircraft crashed on approach to Buffalo, New York on 12 February 2009.

Previously Colgan has argued that the captain in response to the stickshaker stall warning pulled back on the yoke rather than release pressure as he was trained to do.

During the board's final public hearing today to release probable cause, the director of NTSB's office of aviation safety Tom Haueter said he had never seen a pilot react to stall event in the same manner as the captain of the Colgan aircraft.

Four contributing factors were identified by the board including failure of the crew to monitor airspeed warnings, the crew's failure to adhere to sterile cockpit rules, failure by the captain to effectively manage the flight and inadequate procedures at Colgan for airspeed management and approach in icing conditions.

A request by Board chairman Deborah Hersman to add fatigue as a contributing factor was rejected by vote of NTSB staff. Hersman believes the fatigue of the pilots "chipped away at margins of safety the crew believed would insulate them".

Both pilots commuted to the Newark domicile. The first officer arrived from Seattle on the day of the flight while the captain was reportedly awake after 3:00EST on 12 February using the Colgan computer system.

Former US Airways pilot and board member Robert Sumwalt succeeded in his request to add a statement to the 45 existing findings listed by the investigators indicating the Bombardier Q400 lacked a low-speed awareness system similar to other aircraft that feature an amber light on the primary flight display to alert the crew of decreasing speed.

Sumwalt believes such a feature could have accelerated the crew's detection of the low speed situation.

Hersman was also successful in reversing one finding that originally stated an aural warning was not necessary prior to stickshaker activation.

Hersman's request was granted despite Haueter explaining during the hearing that he was not convinced pilots would have acted differently if an aural alert had activated.

The board plans to issue 23 safety recommendations to FAA as a result of its findings from the crash.

Source: Air Transport Intelligence news