The crew earlier requested a descent to avoid haze, lowered the landing gear and then extended the flaps, the 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 six miles from the airport runway, killing the 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 previous calamities due to icing. 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 chilly air was 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 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 at a news briefing in Amherst on Friday afternoon. "With too much buildup of ice, the shape of the wing can change, requiring different airspeeds."

The crash of Continental Connection Flight 3407 from Newark came less than a month after the remarkable Jan. 15 ditching of US Airways Flight 1549 in the Hudson River, in which all 155 people aboard survived. Thursday's flight was operated for Continental by Colgan Airways.

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.

Experts said Friday that ice can build up several ways, and that moving the flaps can lead to loss of control.

This article appeared on page A - 6 of the San Francisco Chronicle