Attendant Takes Pilot's Seat, And Three Are Fired The Pilot Lost His License. He, The First Officer And The Attendant Lost Their Jobs.

To the passengers on USAir flight 528, landing at Philadelphia International Airport shortly after 6 p.m. on April 28, nothing seemed amiss.

The landing after the trip from Tampa, Fla., was routine, and the passengers filed off the Boeing 737 jet.

But behind the closed door to the flight deck, some strange - and, the Federal Aviation Administration says, dangerous - behavior was going on.

The FAA said yesterday that it had revoked the flight certificate of the captain on the flight, Jon L. Swartzentruber, a 12-year veteran pilot with USAir, for allowing an off-duty flight attendant to sit in his chair while the first officer, Kenneth C. Burkins, landed the airplane.

Swartzentruber, a resident of Schwenksville, Montgomery County, was sitting in the jump seat immediately behind flight attendant Jane Zweber while she occupied his place, the FAA said. Zweber was flying free as an off-duty USAir employee while three other flight attendants worked in the cabin of the plane.

USAir went a step further than the federal agency. It fired the three crew members, who were all assigned to USAir's flight-crew base at Philadelphia.

The airline said Burkins was in control of the airplane during the landing. In a report on the incident, the FAA said, however, that the jet's auto-pilot system was not in use during the landing, which means that Zweber could have affected the plane's operation by touching the control yoke or instruments.

The FAA said in a statement that it had determined that Swartzentruber had operated the jet "in a careless or reckless mannner."

FAA spokesman Duncan Pardue said the agency was still investigating the incident, and hadn't decided what it might do to Burkins or Zweber.

USAir chairman Seth E. Schofield said in a statement that the airline's own ''investigation assured me that this completely inexcusable action by three employees was an isolated incident. Nevertheless, this information is particularly painful for all of us . . .

"Despite the isolated nature of this incident," Schofield added, "I wish to reiterate emphatically that no deviations from or violations of safety rules and procedures will be tolerated. . . . I am writing letters to each of the passengers on the flight to apologize for the incident . . . ."

USAir said Swartzentruber was hired by the airline on Jan. 21, 1981. He had 12,300 total flight hours, including 2,600 in twin-engine 737s.

A woman answering the phone at Swartzentruber's home yesterday said, ''We're not going to talk about" the incident.

Burkins had worked for USAir since March 23, 1987, and had 12,000 total flight hours, 2,200 of them in 737s, the airline said.

Zweber had been a flight attendant since March 23, 1989. USAir did not release her hometown.