NTSB Hearing on Buffalo Crash May Hinge on Pilot's Stall Action
The National Transportation Safety Board has scheduled a May 12-14 public hearing involving all of its board members at its Washington, D.C., headquarters to examine "a wide range of safety issues" in the Feb. 12, 2009, crash of Colgan Air flight 3407 near the Buffalo, N.Y., airport. The cause of the crash is not clear, but aviation experts speculated yesterday that what NTSB said about how the pilot responded to a stall warning and stick shaker -- exerting a 25-pound pull on the yoke, which raises the plane's nose -- appears to be the opposite of what should normally be done by a pilot to avert a stall. The crash killed all four crew members, all 45 passengers, and one person on the ground in a house struck by the plane.
NTSB's release said there is evidence ice accumulated on the plane, but the Bombardier Dash 8-Q400 "continued to respond as expected to flight control inputs throughout the accident flight. The FDR data also shows that the stall warning and protection system, which includes the stick shaker and stick pusher, activated at an airspeed and angle-of-attack (AOA) consistent with that expected for normal operations when the de-ice protection system is active."
"The airplane's stick shaker will normally activate several knots above the actual airplane stall speed in order to provide the flight crew with a sufficient safety margin and time to initiate stall recovery procedures," according to NTSB. "As a result of ice accumulation on the airframe, an airplane's stall airspeed increases. To account for this potential increase in stall speed in icing conditions, the Dash 8-Q400's stall warning system activates at a higher airspeed than normal when the de-ice system is active in-flight to provide the flight crew with adequate stall warning if ice accumulation is present. Preliminary airplane performance modeling and simulation efforts indicate that icing had a minimal impact on the stall speed of the airplane. The FDR data indicates that the stick shaker activated at 130 knots, which is consistent with the de-ice system being engaged. FDR data further indicate that 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 Gs. 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. Airplane performance work is continuing."
Post-mortem tests of the first officer were negative for alcohol, illicit substances, and a wide range of prescription and over-the-counter medications, while tests from the captain were negative for alcohol and illicit substances and positive for diltiazem, a prescription blood pressure medication that had been reported to and approved for his use by the Federal Aviation Administration, NTSB noted.
Safety issues that will be discussed at the hearing include icing effect on the airplane's performance, cold weather operations, sterile cockpit rules, crew experience, fatigue management, and stall recovery training. "The tragedy of flight 3407 is the deadliest transportation accident in the United States in more than seven years," Acting NTSB Chairman Mark Rosenker said. "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."
The board said it is also examining a recent event involving a Dash 8-Q400 operated by Colgan in which the plane's stick shaker activated during approach to the Burlington International Airport in Burlington, Vt., with the plane landing normally thereafter. NTSB investigators have conducted interviews with the pilots and check airman on board this flight and will continue to investigate the incident. Also still being investigated are reports of airplane deviations resulting from distortion of the instrument landing system signal for runway 23 at the Buffalo airport.
The Buffalo News and The Washington Post have posted discussions of the release today.