SEATTLE >> A Sea-Tac airport spokesman says all passengers were safely evacuated after a United Airlines plane caught fire before taking off.

The Seattle Times reports that firefighters responding on Saturday discovered flames coming from the auxiliary power unit of United flight 776, a Boeing 757 that was scheduled to depart at 10:30 p.m., bound for Dulles International Airport in Washington, D.C.

Sea-Tac spokesman Perry Cooper says firefighters extinguished the flames, and the plane was evacuated. A preliminary investigation indicated that the fire might be traceable to residual oil in the auxiliary power unit, which is located in the plane’s tail.

The plane was towed to cargo services for further investigation.

United’s website indicated that the flight’s passengers were to be put on another plane a couple of hours later.

The plane that caught fire came to Sea-Tac from Chicago’s O’Hare International Airport, the airline’s website said.