ROMULUS, Mich. — Failure by the pilot to deploy the wing flaps of his aircraft may have caused the crash of Northwest Airlines Flight 255 in which at least 154 people died, federal investigators indicated Wednesday night.
John Lauber, head of the National Transportation Safety Board investigating team, said that the "black box" flight data recorder recovered from the aircraft indicated that the flaps and slats were in an "unusual" retracted position when the plane attempted to take off.
He said also that the pilot and first officer may have omitted a mandatory preflight check designed to make certain the flaps and slats were working properly.
Cockpit conversations taped by the voice recorder recovered from the wreckage indicated that, when the pilot and first officer went through their preflight check, they omitted mention of the flaps and slats, which are included on the checklist, Lauber said.
There was no explanation for those omissions.
Pilots have to rely on instruments to make such checks, because the wings are not visible from the cockpit. Thus, it is not known whether any failure to deploy might have been a deliberate decision on the part of the flight crew, an omission or some mechanical malfunction possibly overlooked during the flight check.
Flaps and slats are large metal surfaces that normally are extended during takeoff to provide a plane with extra lift.
On Wednesday night, Lauber stressed that, although the flight data recorder indicated the flaps and slats were not deployed, further evidence is needed to prove this conclusively.
Unsure of Data
"We can't even be sure that the data on the flight data recorder accurately reflected the circumstances," he said.
Lauber said his investigators would have to look at filaments in the cockpit instrument indicator lights, study the wreckage of the control surfaces themselves and compute performance data on the ill-fated flight to see if the black box readings were correct.
The MD-80 jetliner crashed Sunday on takeoff from Detroit's Metropolitan Airport on a flight to Orange County's John Wayne Airport.
Wednesday was the third straight night in which investigators offered new evidence as to what may have led to the crash.
On Tuesday night, Lauber had indicated that a weather phenomenon known as wind shear, which can generate powerful down drafts and tail winds, may have contributed. He did not discount wind shear on Wednesday night.
On Monday night, the NTSB member told of evidence that led to early speculation that the jetliner had suffered engine failure. Subsequent investigation seemed to reduce that likelihood, and Lauber said Wednesday night that the data recorder indicated that both engines were producing approximately the same thrust and there was no fire in the engines prior to impact.
In discussing the apparent lack of flap deployment, Lauber called it unusual but noted that "it is a permissible configuration in the aircraft."
However, aviation sources indicated that a "no-flaps" takeoff would normally be attempted only on extremely long runways with a relatively light load.
Flight 255 took off on a runway of average length--8,500 feet. The plane, while it has an allowable maximum gross weight of 149,500 pounds, weighed only about 5,000 pounds less than that on takeoff, according to records recovered by investigators.
Lauber said evidence was that the plane reached a maximum altitude of 48 feet.
The plane clipped a 41-foot-tall light pole, glanced off a car rental agency building and slammed into an intersection before skidding more than a quarter of a mile down the roadway in a sheet of flame, striking at least three motor vehicles.
Lauber said Tuesday night that sensing devices at the airport detected potential wind-shear conditions about a half hour before the crash, and advisories were issued on recorded weather broadcasts usually monitored by pilots before takeoff.
Witness reports of flames surrounding the plane's left engine on takeoff led to early speculation that the jetliner had suffered engine failure.
But Lauber said preliminary examination found no evidence that either of the plane's two engines had failed, and aviation experts said the flames may have resulted from an engine backfire.
It's up to Lauber's investigators to sort all this out--a job that is expected to take months.
The first step in that process is the collection of evidence, and that's what the 100 or so investigators are doing right now. That job should be largely completed within about 10 days.
The second step is inspection and interpretation. Some of that takes place at the crash site, some at safety board laboratories in Washington and some at the facilities of the various companies that have manufactured components of the plane.
Voice Recorder Removed