AMHERST, N.Y. — The crew of the plane that crashed on approach to the Buffalo airport Thursday night, killing 50, reported "significant ice buildup" on the wings and the windshield minutes before hitting a house and exploding into an intense fire, a federal transportation official said Friday.
The crew, having earlier requested a descent to avoid haze, lowered the landing gear and then extended the flaps, the movable panels on the rear edge of the wings that allow a plane to maintain lift as it slows, according to the flight data recorder.
But the plane immediately experienced "severe pitch-and-roll excursions," meaning that the nose pointed up and down and the wings wagged from side to side, said Steven Chealander of the National Transportation Safety Board.
Within 40 seconds, the plane crashed, at a steep angle, into a white and gray wood-frame house in the hamlet of Clarence Center, N.Y., about 6 miles from the airport runway, killing a 61-year-old man who lived inside.
Chealander, a former airline captain, stressed that the safety board was in a fact-gathering stage and could not yet determine the cause of the crash, but the sequence he described is consistent with that in previous icing calamities.
The plane, a Bombardier Dash 8 Q400, is certified for flight into known icing conditions, and there is no indication that the light snow and the chilly air were unusual for Buffalo in February.
The investigation was proceeding with unusual speed. Chealander described the cockpit voice recorder, which captured two hours of conversation, and the flight data recorder, with 250 instrument measurements, as being of "excellent quality." He said the data recorder documented the use of the anti-icing system on the plane, which had 74 seats and twin turboprop engines, but did not show whether it worked.
"Significant ice buildup is an aerodynamic impediment," Chealander said. "With too much buildup of ice, the shape of the wing can change, requiring different airspeeds."
Flight 3407 was scheduled to depart at 7:10 p.m. but was delayed until 9:19 p.m. because of storms. It crashed about an hour later.
Within the last 30 minutes of flight, the crew asked to descend to 12,000 feet from 16,000 because of the haze. Shortly afterward, the plane was cleared to 11,000 feet.
According to flightaware.com, a Web site that tracks commercial and private planes by radar, the plane descended steadily from 13,800 feet at 10:01 p.m. to 5,300 feet at 10:11 p.m.
The crew's final communication with the tower, according to an audiotape released by liveatc.net, came at 10:16 p.m., when the plane was to be at 2,300 feet. The controller called for the plane three times and got no response, then asked the pilot of a nearby Delta Air Lines plane whether he could see it. "Uh, negative," the Delta pilot responded.
"Colgan 3407, Buffalo Tower, how do you hear?" the controller tried again. Then the tower called for local police "to find out if anything's on the ground."
Several other pilots in the area reported seeing ice, according to the audio from the tower.
"We picked up some on the way down. I don't think we're building up any more now," said one pilot, suggesting that temperature and moisture between 6,500 and 3,500 feet had caused icing.
Experts said Friday that ice can build up several ways and that previous accidents, including the 1994 crash of an American Eagle turboprop in Roselawn, Ind., have shown that moving the flaps can lead to loss of control.
Gregory A. Feith, a former investigator with the safety board, said that on some planes, moving the flaps changes the air flow in a way that could cause the tail to stall, or lose lift, making it hard to control the angle of the nose. If the ice buildup differed on one side of the tail from the other, he said, the plane would roll; moving the flaps could make it worse.
The crash of Continental Connection Flight 3407 from Newark, N.J., came less than a month after the remarkable Jan. 15 ditching of US Airways Flight 1549 into the Hudson River, in which all 155 people aboard survived.
Thursday's accident was the first fatal crash of a commercial flight in the United States since a ComAir regional jet went down in Kentucky in 2006 and the deadliest since November 2001, when American Airlines Flight 587 landed in a neighborhood in Queens, killing 265 people, including five on the ground.