MERRILLVILLE, Ind. -- The American Eagle plane that crashed Monday night took an unexplained dip to the right, recovered, dipped again and turned upside down just before it plunged to the ground, killing all 68 people aboard, the chairman of the National Transportation Safety Board (NTSB) said at a briefing last night.
Data from the cockpit voice recorder and the flight data recorder from Flight 4184 showed that the plane began descending probably in response to instruction radioed to the pilots from the ground.
As the plane picked up speed, an alarm sounded, indicating that the plane was moving too fast to have its flaps extended.
The flight data recorder showed that the flaps began to retract, but "the onset of an abnormal event then occurred, as the airplane was descending through 9,400 feet," said James Hall, NTSB chairman.
The ailerons, devices near the ends of the wings, moved rapidly to make the right wing dip.
"A recovery from the right roll was initiated," Mr. Hall said. "Then, the airplane rolled sharply to the right. The airplane rolled over on its back, and a recovery was not accomplished."
The anti-icing devices on the wings were turned on, but Mr. Hall said investigators did not yet know if aileron movement was related to icing.
Some aviation experts have also suggested that the plane, which spent 32 minutes in a holding pattern before it disappeared from radar screens, might have been brought down by ice buildup on the wings.
The plane spent most of that time at 10,000 feet. At those altitudes, the temperature was probably below freezing, and rain was heavy at the time, conditions that can lead to ice buildup.
Investigators have not yet put all the data from the cockpit voice recorder, the flight data recorder and air traffic control together. That process will start today in Washington.
Examination of the engines shows that they were running on impact.
The plane had plenty of fuel, about 500 gallons, when it radioed in 15 minutes before the accident. Examination of maintenance records and weather data and the pilots' records have not turned up any particular problems yet, he said.
Investigators are still in the process of reassembling the wings and other critical components found in the soybean field to see if anything important is missing. If so, a wider area will be searched.
Beside a buildup of ice, aviation experts said, an engine malfunction, a collision with a bird or any number of other problems could have caused the roll. In a roll, when one wing drops, the plane loses lift and the nose points down.
For the second day, investigators wearing head-to-toe gear to protect them from disease pored over the scattered remnants of the aircraft, looking for clues to why it crashed and how it broke into such strikingly small pieces.
Trying to preserve any evidence the wreckage might hold, the investigators did not start removing the remains of the 68 victims until yesterday afternoon.