The probable cause of the fatal Colgan Bombardier Q400 crash last year was the captain's inappropriate response to a stickshaker activation warning.
That is the conclusion of the US National Transportation Safety Board's investigation into the 12 February 2009 accident. The NTSB says the captain's response, which was to pull back on the control column, sent the aircraft into an "accelerated aerodynamic stall" from which it did not recover.
Contributing to the cause were the crew's failure to adhere to sterile cockpit procedures and to monitor airspeed effectively, leading to the loss of speed that caused the stickshaker stall warning system to activate. All four crew and all 45 passengers were killed in the accident, which occurred during an approach to Buffalo, New York in night visual meteorological conditions.
During the final public hearing to release the probable cause, the director of NTSB's office of aviation safety Tom Haueter said he had never seen a pilot react to a stall event in the same manner as the captain of the Colgan aircraft.
The captain's response in pulling back the control column was described as "aggressive", creating an acceleration of 1.5g. The board says it does not believe the captain's action was an attempt to deal with a perceived tailplane stall.
Four contributing factors were identified by the NTSB: failure of the crew to monitor airspeed warnings on the primary flight display; failure to adhere to sterile cockpit rules; the captain's poor management of the flight; and inadequate procedures at Colgan for airspeed management and approach in icing conditions.
A request by NTSB chairman Deborah Hersman to add fatigue as a contributing factor was rejected by a vote of the safety board's staff. Hersman believes the fatigue of the pilots "chipped away at margins of safety the crew believed would insulate them".
But the NTSB noted that the pilots had commuted a long way before this duty and had failed to ensure that they had sufficient rest. Colgan was criticised for failing to monitor crew practices relating to fatigue risk management.
The board plans to issue 23 safety recommendations to the US Federal Aviation Administration as a result of its findings from the crash. These include recommendations that aircraft should have an aural as well as a visual low-speed alert and that all pilots should receive training in professional attitudes to their job, with co-pilots being trained for captaincy to receive leadership training.
The recommendations also say that detailed records of pilot training results should be kept, and that training to address performance lapses must be provided; pilot training on type should include recovery from fully developed stalls; and airlines should be required to operate a flight operations quality-assurance programme.