FAA Records of Ill-Fated USAir Jet Show History of Minor Mechanical Problems : Maintenance: Aircraft made six unscheduled landings and one in-flight engine shutdown. But incidents were considered ‘very normal.’

Minor mechanical problems caused six precautionary unscheduled landings and one in-flight engine shutdown during the seven years that USAir owned the Boeing 737-300 involved in Thursday’s fatal crash near Pittsburgh, according to Federal Aviation Administration records.

The aircraft, registered in October, 1987, by the FAA with tail number N513AU, amassed 28 “service difficulty reports” during its life span. None of the problems appeared to pose a serious threat to flight safety, nor do any of them shed light on why the plane plummeted to earth Thursday.

Twelve of the reports were filed by mechanics during the aircraft’s “heavy maintenance check,” a lengthy process that was completed on Feb. 3, 1993. They charted a couple of small cracks in the floor of the fuselage and several small areas of corrosion of floor beams. All were repaired.

As of its last flight, the plane had flown 23,846 hours since new and had made 14,489 takeoff and landing cycles, according to USAir spokesman Richard Lesman. He characterized the FAA reports as “very normal . . . nothing out of the ordinary.”

A former 737-300 pilot for a competing airline who reviewed the service difficulty reports with a Times reporter agreed that the plane had experienced comparatively few problems.

The plane’s first unscheduled landing documented in the reports happened Aug. 21, 1989, after the outer right main landing gear tires blew out on takeoff from Pittsburgh, damaging the flaps and gear landing doors. The plane flew an oval holding pattern near the airport to burn fuel and lighten its load prior to an uneventful landing.

The next incident was Nov. 17, 1989, when a warning light indicated that the anti-skid braking system was inoperative. That flight from Baltimore to Cleveland returned to Baltimore, which had the longer runway. Mechanics there replaced two electrical relays and a switch.

On Sept. 9, 1991, en route from Baltimore to Las Vegas, the pilots felt a “low frequency vibration similar to high-speed buffet” and diverted for a precautionary landing at Pittsburgh, where USAir has its main hub. Mechanics couldn’t find a cause, according to the FAA report.

A light warning that the aft cargo door was opened illuminated on ascent from Orlando, Fla., on Oct. 30, 1992, and the plane returned and landed without incident. A rear cargo door snubber spring was replaced.

While on a flight from New York’s LaGuardia Airport to Tampa, Fla., on Feb. 7, 1993, instruments indicated that the right engine of the aircraft was producing too much power for its throttle setting. The plane landed in Baltimore where mechanics replaced an engine control motor that had seized.

The last unscheduled landing documented in the reports occurred on Feb. 6, 1994, when the flight crew was unable to pressurize the plane after takeoff from Philadelphia and a flight attendant reported the sound of rushing air at the forward entry door. After returning for landing, the door was found improperly closed. The closing mechanism was tested successfully several times and the plane took off again.

The in-flight engine shutdown happened on July 5, 1989, when the flight crew saw that oil pressure in the left engine had gone to zero. The engine was immediately shut down and the flight from Pittsburgh continued for an uneventful landing at its Philadelphia destination. The plane flew 15 minutes on a single engine. Mechanics replaced an engine starter shaft seal, filled the engine with oil and put the plane back in service.

The FAA has rules governing aircraft maintenance, including one specifying that a new jetliner must undergo its first heavy maintenance at 20,000 hours of flight time, and thereafter every 11,000 hours.

USAir gave N513AU its first heavy maintenance check at 18,622 hours. The process, in which the aircraft is opened and thoroughly inspected, appears to have taken about a month to accomplish, according to the reports.