AMHERST, N.Y. — The commuter plane that crashed near Buffalo on Thursday night slammed to the ground flat on its belly, with almost no forward momentum and facing opposite its intended route, seconds after two automatic warnings to the pilots that the plane was not moving fast enough to stay aloft, the National Transportation Safety Board said on Saturday.
Officials hope to have all of the wreckage of the Continental flight in Clarence Center, N.Y., moved by Wednesday. More Photos »
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Victims of Flight 3407
The description indicates that the plane, a Bombardier Dash 8 Q400, suffered an aerodynamic stall, meaning the flow of air over the wings was either disrupted or too slow to sustain flight, but the reason why remains a mystery.
Icing, which the crew of the plane reported shortly before the crash, is one possible reason, but Steven Chealander, the safety board member assigned to the investigation and a retired airline captain, said the aircraft had a sophisticated ice protection system.
The plane was equipped, he said, with pneumatic boots, which are a bit like tires, on the front edges of the wings, the tail and the vertical stabilizer, that inflate and contract twice a minute to break ice accumulations, as well as electrically heated propellers. The system gives an indication in the cockpit if any boot is not working, and so far, investigators have found no sign of such an indication, Mr. Chealander said.
“This Dash 8 is a workhorse airplane,” he said. “It’s not really susceptible to ice.”
Investigators searching the crash site for evidence have described a fire so intense that on one of the plane’s two propellers, all six blades were completely destroyed. The blades are made of a mixture of polyurethane and carbon. Past crashes have been caused by broken blades.
The Federal Bureau of Investigation has been scouring the neighborhood for parts that were thrown off before the plane hit the ground but have not found any, investigators said.
The flight, Continental Connection Flight 3407, began from Newark Liberty International Airport and was headed for Buffalo Niagara International Airport. It crashed into a house in the hamlet of Clarence Center, about six miles from the Buffalo airport, killing all 49 people on board and one person in the house.
Firefighters had pumped water on the smoldering wreckage for so many hours that the site became covered with ice, further complicating the investigation. On Saturday, volunteer firefighters and other workers used torpedo-shaped heaters to melt some of the ice, Mr. Chealander said. They were working in a cramped space in which the wreckage of the house is mixed with that of the plane and with the remains of the dead.
The medical examiner expects to take three or four more days to remove the bodies, Mr. Chealander said.
Investigators are hoping to have all the wreckage recovered before Wednesday, when a major snowstorm is expected.
According to investigators, the last minute of flight, as described so far, unfolded this way: As the plane flew about 1,600 feet above the ground, southwest toward a runway at the Buffalo airport, the crew lowered the landing gear. Twenty seconds later, one of the two pilots set a lever to extend the flaps, movable metal panels on the back of each wing, to 15 degrees, a standard step before landing.
Immediately, the airplane’s nose began to pitch radically up and down, and soon after, the airplane rolled left and right. A stick shaker, a device that warns that the plane is flying so slowly that its wings are about to stall, losing lift, gave its warning by shaking the yoke in the pilots’ hands. Then the stick pusher came on, a system that literally takes matters out of the pilots’ hands by pushing the yoke forward, to push the nose down and increase airspeed to avoid stall.
The crew increased engine power, but never regained control: the plane hit the house, having spun around to face northeast, although it had been flying southwest. It happened so fast that the flaps never made it to 15 degrees.
And the plane was moving so slowly that it hit only a single house in the densely settled neighborhood. A garage behind the house remained intact.
The cockpit voice recorder, which investigators will examine more thoroughly on Sunday, recorded the captain and the first officer noting ice on the windshield and the leading edge of the wing. The crews of other planes also noted icing conditions. But there is nothing yet to indicate that conditions were unusual for a February night in the Buffalo area.
Icing could cause the pitch and roll investigators have described.
In the past, icing conditions have caused problems with the tail of a plane when the flaps are moved on the main wing.
In normal flight, the wing holds the plane up and the tail exerts a downward force. The plane itself is like a seesaw; downward force on the tail keeps the nose up. If the tail stops working properly, the nose drops.
When the flaps are extended on the main wing, there are at least two possible effects on the tail. One is that as the shape of the wing changes — which is the purpose of extending the flaps — the nose on a plane like the Q400 will lower a bit. That changes the angle at which the wind hits the tail and at a new angle, ice on the tail may further disrupt the tail’s function.
Extending the flaps also may slow the plane down. Every wing, as well as the tail, has a stall speed, a minimum speed below which it will not function correctly. As the wing is covered with ice, the stall speed increases. If the plane slows down, it may drop below the tail’s new stall speed.