Federal investigators have found new evidence that the right engine of the USAir jet that crashed on Thursday might have malfunctioned during flight, officials of the National Transportation Safety Board said on Sunday night.
The evidence, while not conclusive, increased their suspicion that the engine's thrust reverser, a braking mechanism, might have partially deployed. They also said that engine's thrust reverser had been repaired a little more than two months ago.The Boeing 737-300 suddenly rolled to the left and plunged from more than a mile high, after an uneventful flight from Chicago. The crash killed all 132 people aboard.
The investigators said they are making a special effort to retrieve parts of the right engine to determine whether its thrust reverser, which is used to slow a plane after it lands, was inadvertently deployed.
Carl W. Vogt, a member of the National Transportation Safety Board, said on Sunday night that the investigators had now found three of the six actuators that control the position of the right engine's thrust reverser in a deployed condition and one that was not deployed.
He said that the outer part of the cowl, which allows the thrust reverser to operate, was found in a nonextended position but that the inboard part had not been found.
"We suspect, therefore, that the three extended actuators may relate to the inboard cowl or sleeve, and we have not yet found that," he said.
Each of the plane's two engines, one under each wing, is encased at the rear by a sleeve made up of two cowls.
In normal use of the thrust reversers, all the sleeves move simultaneously back, allowing deflectors to divert the engines' blast outward, creating a powerful braking force. Each of the two cowls on an engine is driven by three actuators that extend to drive the whole mechanism.
It now appears possible that the inboard cowl on the right engine was driven back by its three actuators. If that happened, the jet blast on half of the right engine would be deflected, possibly causing an unusual twisting force on the plane's right wing.
Vogt said that there was a crew report on June 28 that the right engine thrust reverser would not deploy, and subsequent reports indicated there was difficulty with it. On July 3, a portion of the mechanism on the right engine thrust reverser was replaced, and there were no subsequent reports of difficulty, he said.