RELATED: Remembering the victims of Flight 3407
The National Transportation Safety Board said information obtained from the craft's data recorder shows the stall warning system had activated before the accident and there was some ice accumulation, but no mechanical problems were found with the plane.
The data "shows that some ice accumulation was likely present on the airplane prior to the initial upset event, but that the airplane continued to respond as expected to flight control inputs throughout the accident flight," the board said in a statement.
Continental Connection /*Flight 3407*/ was about five miles short of the Buffalo Niagara International Airport, flying in icing conditions the night of Feb. 12 when the plane tumbled out of control and plummeted onto a house. All 49 people aboard the plane and one man in the house died.
The board said data shows the speed of the Dash 8-Q400 Bombardier, a twin-engine turboprop, had slowed to 150 mph when the aircraft's stick shaker activated - the device warns pilots of an impending stall by shaking the control yoke. When that happened, the board said, the plane continued to slow and "there was a 25-pound pull force on the control column," forcing the aircraft's nose up.
Aviation safety experts said pulling back increases a stall, and that pushing forward and increasing airspeed would have been the correct response.
"Pulling up is the wrong thing to do when the airplane is giving you a stall warning," said William Waldock, a professor of safety science at Embry Riddle Aeronautical University who has investigated accidents for more than 30 years. "You increase the airspeed by pushing the nose down. He's pulling up fairly abruptly. There's an old adage that airspeed is life."
"It's sounding more and more like a human-factors accident," Waldock said. "This is a little bit different scenario than I think what everybody thought at first."
A key question from the beginning of the board's investigation has been whether the plane experienced an aerodynamic stall caused by icing and the pilot's reaction to the stall. Ice accumulation can change the shape of a plane's wings, causing it to lose lift.
Turboprops rely on deicing boots on the leading edge of the wings that inflate and deflate to break up ice. The decades-old technology isn't as effective as the deicing systems on jetliners, which direct engine heat to the wings to melt ice.
Former NTSB accident investigator Greg Phillips said it appears so far that the ice in the Buffalo crash "wasn't anything the plane shouldn't have been able to handle."
Investigators are continuing to examine aircraft's deicing system and to probe the flight crew's training, the board statement said.
The information from the data recorder doesn't indicate any problem with "the airplane's systems, but you still have to leave the possibility of the icing system operation open until those examinations are complete," Phillips said.
The NTSB has scheduled an unusual three-day public hearing in which all five board members will be present for May 12-14 on the Buffalo crash. The hearing will cover a range of safety issues, including the icing effect on the airplane's performance, cold weather operations, sterile cockpit rules, crew experience, fatigue management, and stall recovery training, the statement said.
"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 in the statement. "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 has held only two similar hearings in the last 12 years:
-A 2002 hearing into the crash of American Airlines Flight 587 in a New York City residential neighborhood just two months after the Sept. 11, 2001, terrorist attacks. The board attributed the cause of the crash, killed 260 aboard and five people on the ground, to the copilot's response to turbulence shortly after takeoff.
-A 1997 hearing on TWA Flight 800, which broke apart off the coast of Long Island, N.Y., after a fuel tank explosion. All 230 people aboard were killed in the 1996 accident.
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Associated Press writer Seth Borenstein contributed to this report.
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