Federal investigators say the Colgan Air Bombardier Q400 that crashed on approach to the Buffalo Niagara International Airport Thursday night landed in a relatively flat attitude, despite eyewitness accounts that suggested a nose-dive.
The aircraft was also oriented in the opposite direction of the instrument approach to Runway 23 at the airport.
Colgan 3407, enroute to Buffalo from Newark as a Continental Express flight, crashed into a house in a neighborhood about 5mi from the airport after the crew experienced violent pitch and roll excursions after deploying the first increment of flaps (15 degrees) in preparation for landing, information gained from the flight data recorder.
NTSB board member Steven Chealander, speaking to reporters today from Buffalo, says further review of the cockpit voice recorder (CVR) also shows that stick shaker and stick pusher, devices that attempt to prevent pilots from entering an aerodynamic stall, had activated after the upset.
Chealander yesterday reported that intial review of the CVR showed pilots discussing "significant" ice build-up on the wings and windshied.
That evidence, combined with the aircraft attitude, may suggest the aircraft remained in a stalled state from upset at approximately 701m (2,300ft) altitude to the crash, a result that is not uncommon in fatal turboprop accidents.
An April 2006 report by the Flight Safety Foundation of stall recovery events in turboprops reveals that in three accidents that killed 134, pilots did not initially reduce the angle-of-attack on the aircraft by moving the control column to the nose-down position early in the upset sequence.
The pilots of Colgan 3407 had extended the landing gear 20 seconds before deploying the flaps, and had attempted to retract both during the upset that followed the flap extension. All 49 onboard perished in the accident as well as one person in the house.
The picture below, taken by the Buffalo News, shows the relative orientation of the aircraft at the crash site.
Chealander says investigators are reviewing maintenance records at Colgan’s base in Virginia and that earlier reports that the aircraft was delayed out of Newark because of a mechanical problem were false. High winds at Newark had delayed the flight however. The aircraft’s Pratt & Whitney Canada PW150 engines appear to have been generating torque at the time of the accident, investigators say.
The crew did not discuss any caution lights related to the pneumatic deicing boots on the wing leading edges as well as horizontal and vertical stabilizer leading edges, says Chealander, indicating that the system, as well as systems for the engine inlet cowlings and propellers, appears to have been operating properly.
A cursory look at the US Federal Aviation Administration’s service difficulty report (SDR) database for the Q400 model reveals at least three instances, all in 2002, where Q400 wing leading edge pneumatic deicing systems failed to work properly due to a faulty dual distributing valve built by Aerazur, a subsidiary of Zodiac. In each case the caution lights were illuminated however. All Nippon airways had earlier reported a high removal rate for the distributing valves, in most cases because the caution light had illuminated. Aerazur in 2007 switched parts to address the problem.
Colgan, a subsidiary of Pinnacle Airlines, purchased N200WQ nine months ago.