Workers continued the grim task of recovering dismembered bodies from the wreckage of USAir Flight 427 on Saturday as attention focused on the possibility that a malfunctioning rudder system may have caused the crash of the Boeing 737 jetliner that killed all 132 on board.
Evidence was still sketchy, but experts were studying the similarities between Thursday's crash at Pittsburgh International Airport and the crash of a United Airlines 737 four years ago near Colorado Springs.
Both planes suddenly rolled over, went into a steep dive and crashed nose first as they were preparing to land.
The cause of the 1990 crash has never officially been determined. But the National Transportation Safety Board listed two possible causes: severe rotating winds or a malfunctioning rudder system.
Investigators also found that one of six thrust reversers recovered so far had been accidentally deployed but said it may have happened on impact and it appeared to be an unlikely factor in the crash.
Barry Schiff, a veteran airline pilot who has been working on a Justice Department investigation of the Colorado accident, said the rudder failure scenario "seems to make a lot of sense" in the Pittsburgh and Colorado crashes.
He noted that while rotating winds were reported in Colorado, there were no reports of dangerous winds here, "so that sort of leaves you with the rudder in the Pittsburgh crash."
In the 737 and other planes, the rudder is a large, hinged slab on the trailing edge of the tail's vertical fin. Operated by foot pedals, the rudder swings to the right and left, helping a plane turn right or left by pushing the tail in the opposite direction.
Large jetliners like the 737 have a "yaw damper"--a mechanism that automatically deflects the rudder slightly to straighten the plane out when winds buffet the tail from side to side.
Schiff said the pedals do not move when the rudder makes these corrections, and the pilot has no sense that they are occurring.
He said there are growing suspicions that in the Colorado crash, the yaw damper suddenly made an uncommanded full deflection of the rudder--possibly due to some sort of electrical failure in the damper's hydraulic system.
"That would make a plane start to yaw (turn to the side), then roll, then go down steeply," Schiff said.
"That is what the 737 did in Colorado Springs, and apparently that is what the plane did in Pittsburgh," he added. "If . . . (full rudder deflection by the yaw damper) is what happened, the pilots wouldn't feel it on the pedals and they must have wondered what the hell was going on."
In the wake of the NTSB's investigation of the Colorado crash, the Federal Aviation Administration ordered that rudders be inspected regularly on all 737s.
The plane that crashed here was inspected four times this year, the last time less than a month ago, and the NTSB said that no problems had been found.
NTSB investigators say "black box" recordings of what the pilot and co-pilot of Flight 427 said during the final seconds of flight "does not help us much" in determining what went wrong.
NTSB investigators say the plane's other "black box"--a flight data recorder containing 14 different kinds of information on the 737's control settings and performance during the last moments of flight--is expected to provide more clues on what caused the crash.
The investigators interviewed witnesses and studied maintenance records Saturday. They also were able to identify much of the wreckage, and they talked to air traffic controllers who were on duty and flight crews of other planes that were flying near the airport when the crash occurred.
Both of the engines were located. Although one of six thrust-reverse activators from the right engine was found in a deployed position, a source close to the investigation said the deployment probably happened on impact. He said it appears unlikely that thrust reversal was a factor in the crash.
If it was deployed during the flight, the plane probably would have rolled to the right instead of the left, said NTSB member Carl Vogt. Witnesses have all reported that the plane rolled to the left.
Nevertheless, Vogt said, "any evidence that the thrust reverser accidentally deployed is something that demands serious attention."
Thrust reversers are normally deployed after landing to bring a plane to a quick stop. Much like reversing a motor on a vacuum cleaner, they direct the blast forward instead of backward.
But most of the day's efforts were concentrated on the grisly job of recovering mangled human remains on a forested ridge about seven miles northeast of the airport.
The recovery team, working under a warm sun, sweltered in the heavy yellow bio-hazard coveralls worn to protect them from blood-borne pathogens, such as AIDS or hepatitis.
Each body part had to be charted as to location and photographed before it could be removed. The job was slow, painstaking and often heartbreaking.
Most of the information did not provide enough for positive identification. Authorities weren't sure when, or if, the information would be released to the public, or if all the victims could eventually be identified.
"It's still pretty bad up there," said Fred David, chief of the Hopewell Township Police Department, which has jurisdiction in the area. "But at least the weather's better. It's stopped raining."
Human remains were sent to the morgue at a nearby Air National Guard base. There they were tested after they were taken from plastic bags. Labels containing all the information known about the parts were attached to the bags.
"We're trying our best," said Terry Tatalovich, deputy coroner of Beaver County, Pa. "It's a little early in the game to tell."
About 20 coroners from neighboring counties were helping 150 members of the Air National Guard sift through the wreckage.
"They're working as delicately as possible," said Fire Marshal John Kaus. "These are human beings. We're not stacking bodies on top of one another. We're treating these individuals with the utmost respect."
The job was about 60% finished Saturday, and it was expected to be completed on Monday, Kaus said.
Times wire services contributed to this story.
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