PITTSBURGH -- Federal investigators say they have found more evidence to suggest that a system to reverse engine thrust may have malfunctioned on USAir Flight 427 but stressed that it was too early to tell what caused the nation's worst crash in seven years.
Parts found by investigators indicate that the plane's thrust reversers may have been activated, but officials cautioned that they don't know if this occurred in flight or only when the aircraft slammed into a hillside 6 miles from Pittsburgh International Airport on Thursday, killing all 132 on board.
The thrust reverser system is designed to reduce the speed of an airplane upon landing. The system includes "acuators" that extend to slide metal sleeves forward and backward to reverse the engine's thrust, slowing the plane. National Transportation Safety Board member Carl Vogt said that on Saturday investigators found one acuator in the right engine that had extended; yesterday, investigators found two more that were extended. Each engine has six such devices.
Investigators said it could take months before a cause is determined and stressed that it was premature to place the blame on the reverser system. "If you draw a conclusion today," said Mr. Vogt, "you'll probably be wrong when this case is over."
Briefing reporters last night, Mr. Vogt said problems with the engine's thrust reverser system were noted on June 28 when a pilot of the Boeing 737 reported that the system was "difficult" to activate. On July 3, a portion of the system was replaced, Mr. Vogt said, adding that the plane maintenance records did not show any major problems.
He said investigators are examining whether a malfunction in the thrust system would have caused the plane to roll left instead of a more likely roll to the right. Eyewitnesses interviewed by the NTSB said they saw Flight 427 roll left before plummeting 6,000 feet.
Solving the mystery to what caused the crash continued for a fourth day yesterday as investigators examined records from air-traffic control. They also announced that they had found the landing gear, wings, tail and cockpit of the downed aircraft and had determined that a second plane, a twin-engine turbo aircraft, was more than 3 1/2 miles away from Flight 427 and would not have been a factor in the crash.
Mr. Vogt also said that investigators interviewed the crew of the plane who flew it on an earlier leglast Thursday from Charlotte, N.C., to Jacksonville, Fla. "They made very positive statements" about the performance of the aircraft, said Mr. Vogt.
Today, recovery crews may begin removing parts of the wreckage from a crash site that is the size of three football fields. The pieces -- many of which are tiny shards of metal that will be pulled from a crater -- will be assembled and analyzed in a hangar near the Pittsburgh airport. Visible human remains have been transported from the site, and officials say more will be recovered as the wreckage is removed.
As crews did their work at the site, Sen. Harris Wofford, D-Pa., toured the wreckage and seemed amazed by the devastation. "It's a tragedy to see that crater," he said, "The scar is on the families who lost people."
Mr. Vogt gave an indication of the power of the crash when he told reporters that the business card of one passenger was found about 2 miles from the site. The 33 eyewitnesses interviewed told investigators that there were no flocks of birds in the sky and that no parts fell off the airplane before impact. One witness, said Mr. Vogt, said he "heard a sputtering sound" from the left engine. Another reported hearing "explosions after impact."
"We have varying accounts," Mr. Vogt added.