WASHINGTON (AP) - Passengers on a flight bound for San Francisco used emergency parachutes to evacuate a plane at Dulles International Airport outside Washington after the pilot noticed something was wrong with the engine.

Metropolitan Washington Airports Authority spokeswoman Kimberly Gibbs says the United Airlines flight was on the airport taxiway about 1 p.m. Wednesday when the pilot found a problem.

Gibbs says after the passengers were all off, the airplane headed back to the terminal.

It was not clear how many passengers and crew were on board.