Crash Evidence on Wing Flaps Contradictory

Conflicting evidence began to build Thursday as to whether the cockpit crew’s failure to deploy wing flaps and slats on takeoff caused the crash of Northwest Airlines Flight 255.

John Lauber, head of the National Transportation Safety Board investigaton of the crash, said Thursday night that a new witness--the pilot of another Northwest flight--stated “very positively” that the flaps of the ill-fated MD-80 jetliner were deployed during its entire acceleration and liftoff prior to the crash that took at least 154 lives Sunday night.

Flaps Collected

Lauber said that, although all the flaps and wing structures of the stricken jet have been collected for examination by investigators, it is still too early to say whether the flaps were deployed correctly.

“What we have learned is that we have a lot of work to do,” Lauber said.

He said the new witness was a Northwest co-pilot who was wait ing in line to take off after Flight 255, which was bound for Phoenix and Orange County’s John Wayne Airport.

Lauber said another Northwest pilot and a private pilot, both also waiting for the runway, observed the takeoff but did not notice whether the flaps were deployed.

On Wednesday night, Lauber had announced 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 also said that the cockpit conversations taped by the voice recorder recovered from the craft indicated that, when the pilot and co-pilot went through the preflight check mandated under federal law, they omitted mention of the flaps and slats, which are included on the list. There was no explanation for these omissions.

There was one other piece of major evidence that the flaps may have been deployed properly.

Aviation sources noted Thursday that the cockpit crew members normally would have been alerted by an automatic takeoff warning horn if they attempted a liftoff in the wrong configuration--that is, with flaps retracted.

Do Not Hear Horn

But Lauber said Wednesday that investigators listening to the cockpit voice recorder did not hear the horn go off.

“It would be a hell of a coincidence if they forget the flaps and then the horn didn’t work too,” Barry Schiff, a Trans World Airlines pilot, said.

Pointing to the conflicting indications from the flight data recorder and cockpit voice recorder, the Air Line Pilots Assn. said Thursday that these represented “disturbing inconsistencies in evidence.”

And, in a statement released at its headquarters in Washington, the pilots’ union said that there are two “readily apparent scenarios for this inconsistency.”

One involves pilot error, with the crew failing to set the flaps and slats properly and the warning horn failing to sound. The other involves mechanical failure, with the crew setting the flaps and slats properly, but the malfunction causing them not to deploy, at the same time causing the warning system not to sound an alarm.

The union said it could not explain why the cockpit crew apparently omitted the flaps and slats from the mandatory checklist.

Will Study Evidence

Lauber said that investigators will have to study further evidence from the wreckage, recordings and witnesses to resolve these and other issues.

Flaps and slats are large metal surfaces that normally are extended during takeoff to provide a plane with extra lift. Flaps extend from the back of the wing, slats from the front.

Pilots interviewed Thursday said that takeoffs without flaps usually are attempted only when the load is light, the runway is long and the takeoff speed is high.

John Debomy, a veteran military aviator and airline pilot who currently is flying as a first officer for United Airlines, said Thursday that when a fully loaded plane like Flight 255 attempts to take off without flaps, “it can leave the runway, but it can’t fly . . . .

“There’s enough energy for it to leap into the air,” he said, “but there’s not enough lift for it to fly. . . . That’s what the flaps are for.”

Debomy said the only explanation of why the pilots might have failed to deploy the flaps is that “they just forgot . . . .

“Normally, you check the dial (on the instrument panel) and reach for the flap handle to make sure,” he said. “The co-pilot normally does that.

“You’re dealing with professionals, but, you know, they’re also human. There may have been some interruption (while they were running through the checklist) and they just forgot.”

Can’t Answer Question

Schiff, another veteran airline pilot, said he “could not answer” the question of why the cockpit crew of Flight 255 might have attempted a takeoff without first deploying the flaps.

“It’s a ritual of habit,” he said.

Records indicate that the MD-80, weighed about 149,500 pounds when it left the gate, only about 5,000 pounds less than its maximum allowable takeoff weight.

The runway used was 8,500 feet long, about average in length. The takeoff speed has been computed at 142 to 149 knots, which Lauber said is slower than normal for any takeoff without flaps.

According to witnesses, the big plane nosed up sharply as it lifted off and began yawing slowly from left to right and back to left. Lauber said the flight data recorder indicated the jetliner reached a maximum altitude of only about 48 feet before it began to sink.

The plane clipped a 41-foot light pole, glanced off a car rental building and slammed into an intersection before skidding down a roadway in a sheet of flame.

Note ‘Inconsistency’

Aviation sources said the behavior of the plane as it attempted to lift off was consistent with one taking off without flaps properly deployed. But the pilots’ union, calling the absence of a warning horn a “disturbing inconsistency” said that it was misleading to leave the impression that “the accident may have been caused solely by human error.”

FAA records in Oklahoma City disclosed Thursday that a cockpit instrument light--a separate safety device from the warning horn--on the same plane flashed an erroneous warning on June 30 that the flaps were improperly deployed.

The plane, which was approaching Minneapolis when the instrument failure occurred, landed without incident and the instrument was repaired.

Lauber, who is adhering to an NTSB policy of refusing to speculate about what may have caused the crash, has refused to rule out any possibilities.

While most of the attention is focused on the wing flaps, Lauber is continuing to indicate that a weather phenomenon known as wind shear, which can create powerful down drafts and tail winds, may have been a contributing factor.

He said Wednesday night that the pilot of a plane approaching Metropolitan Airport for a landing about 24 minutes before the crash reported encountering wind-shear conditions.