MERRILLVILLE, Ind. - The passengers of Flight 4184 spent 36 seconds in a roller coaster ride of terror before the ATR-72 smashed into the ground Monday.
Five warnings sounded rapidly as the American Eagle plane rolled on its back and fell at a 45-degree angle, investigators said Thursday.
The cockpit voice recorder shows the pilots "attempting to control the aircraft right up to the end of the tape," Jim Hall, head of the National Transportation Safety Board said.
Investigators are unsure if the plane continued spinning as it fell and are trying to recover that information from the flight data recorder.
Meanwhile, American Eagle issued a bulletin to all of its ATR crews prohibiting the use of autopilot during icing conditions. The autopilot was on until Flight 4184 began to roll.
"We issued this for precautionary reasons . . . for the sake of safety," said spokesman Marty Heires.
The NTSB also said:
-- American Eagle advised its ATR-42 and ATR-72 pilots to fly in holding patterns with wing flaps set at zero degrees, as recommended by ATR. The flaps on Flight 4184, which was holding, were set at 15 degrees, which is not prohibited.
-- Simmons Airlines, which operated Flight 4184 as American Eagle, did not give its flight crew an "air met" weather advisory that indicated icing conditions the day of the flight.
-- The captain of an ATR flight that landed in South Bend at 11:30 p.m. the night of the crash told the NTSB he had experienced ice build-up on the wings and that de-icing equipment failed to break it off. He said it produced an extra roll in a bank turn.
Meanwhile, in Washington, D.C., investigators studied the 25-hour tape from the flight data recorder - known as the "black box."
At the crash site, crews continued the task of gathering body parts of the 68 victims.
The remains were placed in plastic bags and carried to a refrigerated tractor-trailer rig parked next to the field. Others pieced the wings together.
The plane's black box was a newer model and recorded 100 parameters. It shows that the steering mechanisms on the wing - the ailerons - moved, causing the plane to roll right and recover. A second roll to the right flipped the plane onto its back as it screamed down.
Investigators have looked at the weather as a factor but decline to speculate about the role of ice that apparently built up on the wings and tail.
They may not have to.
While most crash probes don't provide answers to the icing theories, the flight data recorder on Flight 4184 monitored the de-icing equipment.
The wealth of information contrasts starkly with the crash eight weeks ago of USAir Flight 427 near Pittsburgh. It also rolled right and crashed as it descended, killing all 132 people aboard. That plane's data recorder monitored 11 parameters, and investigators still aren't sure why it crashed.
The flight data and cockpit voice recorders are actually two metal cases painted fluorescent orange.
The most basic recorders monitor altitude, airspeed, pitch and other rudimentary mechanical functions. Some measure only five plane functions, or parameters, while others can record dozens.
"The black box is extremely important," says the NTSB's Charlotte Casey. "The more information you have . . . the better able you are to get an appreciation of what happened."
Planes built before May 26, 1989, are required to have recorders with 11 parameters. Newer ones must have recorders with 17 parameters, says the Federal Aviation Administration's Druce Anderson.
But some airlines are equipping newer planes with recorders that measure 100 or more parameters, like Flight 4184.
Pilots fought for control
The unexplained movement of a steering device left the crew of American Eagle Flight 4184 fighting for control of the plane as it plunged into the ground. The plane's last few minutes:
3:24 p.m. CT Enters holding pattern at 10,000 feet because gusting winds forced a change of runways at O'Hare International Airport. 3:56 p.m. CT Cleared to descend to 8,000 feet, but asked to hold for 10 more minutes. Pilot responds with a `Thank you.' That was the last radio contact. 3:59 p.m. CT Radar contact with plane lost at 4,000 feet.
What the flight data recorder showed: 1. As Flight 4184 begins its descent, crew increases speed from 201 mph to 213 mph. Wing flaps, which regulate air speed, set at 15 degrees. De-icing boots, which clear ice off wings and tail, activated. 2. Flap over-speed alarm sounds, warning pilot plane flying too fast to have flaps extended at 15 degrees. Pilot retracts flaps to 10 degrees. 3. At 9,400 feet, ailerons -- wing surfaces near the tip, used to control rolling and banking -- move rapidly, causing right wing to dip. Crew turns off autopilot to make recovery. 4. Plane rolls sharply right, then on its back. Then it plummets to ground. 5. Plane hits ground nose first at 45 degree angle, shatters into tiny pieces, except for a 6- by 8-foot piece of tail.
Still under investigation Ailerons Controlled by pilots. But plane was on autopilot when ailerons were activated and it is unclear what caused initial dip. Icing Anti-icing device activated at time of crash. Light to moderate icing advisories in effect. Another ATR-72 landed at O'Hare with icy wings and engine trouble about 30 minutes after crash. Wind Winds gusted up to 49 mph in area. Wind shear, sudden changes in wind speed and direction, reported at time of crash. Light to moderate turbulance advisory in effect. Changing winds at 7,000 to 9,000 feet occurring all day without incident.
