By Mary Grady, Contributing Editor
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The NTSB on Wednesday released factual findings from its investigation into the Feb. 12 crash of Colgan Air Flight 3407 in Buffalo, N.Y, in which all 49 on board and one person on the ground were killed. A preliminary examination of the airplane systems has revealed no indication of pre-impact system failures or anomalies, the NTSB said. The flight data recorder shows that the stall warning and protection system, which includes a stick shaker and stick pusher, activated at an airspeed and angle-of-attack consistent with that expected. The Dash 8-Q400's stick shaker will normally activate several knots above the actual stall speed to provide the flight crew with time to initiate stall-recovery procedures, and it activates at a higher airspeed than normal when the de-ice system is active, since icing elevates stall speed. The FDR data indicates that the stick shaker activated at 130 knots, which is consistent with the de-ice system being engaged. When the stick shaker activated, there was a 25-pound pull force on the control column, followed by an up elevator deflection and increase in pitch, angle of attack, and G force. The data indicate a likely separation of the airflow over the wing and ensuing roll two seconds after the stick shaker activated while the aircraft was slowing through 125 knots and while at a flight load of 1.42 Gs. The predicted stall speed at a load factor of 1 G would be about 105 knots.
The NTSB's examination of the FDR data and preliminary evaluation of airplane performance models show that some ice accumulation was likely present on the airplane prior to the initial upset event, but that the airplane continued to respond as expected to flight control inputs throughout the flight. The board has conducted reviews of the weather conditions, the aircraft maintenance records, and tapes of ATC communications with the flight crew. Accident investigators have interviewed the air traffic controllers on duty at the time of the accident, as well as flight crew who had recently flown with and/or provided instruction to the accident crew. Investigators will perform additional examinations on the dual distribution valves in the airplane's de-ice system, which uses pneumatic boots to remove ice from the leading edges of the wings, horizontal tail and vertical tail.
The Safety Board is also examining several other areas potentially related to the accident, including the circumstances of a recent event involving a Dash 8-Q400, operated by Colgan Air, in which the airplane's stick shaker activated during approach at Burlington, Vt. That airplane subsequently landed without incident. The safety board is also reviewing reports of airplane deviations resulting from distortion of the instrument landing system (ILS) signal for Runway 23 at BUF, which was reported in a Notice to Airmen. To date, investigation into these reports has not revealed any connection to the accident flight, the NTSB said. The NTSB will conduct a public hearing on this accident, May 12-14, in Washington, D.C. The hearing will cover a wide range of safety issues, including icing effect on the airplane's performance, cold-weather operations, sterile-cockpit rules, crew experience, fatigue management, and stall-recovery training. "Flight 3407 is the deadliest transportation accident in the United States in more than seven years," said NTSB Acting Chairman Mark Rosenker, in a news release on Wednesday. "The circumstances of the crash have raised several issues that go well beyond the widely discussed matter of airframe icing, and we will explore these issues in our investigative fact-finding hearing."
This accident has been the topic of wide discussion in the aviation community. Click here to go to AVweb's Insider Blog, and find several posts about the accident. Click here for the full text of Wednesday's NTSB report.