An unidentified American Airlines co-pilot was arrested on Saturday at a Detroit airport terminal on suspicion of drinking before his scheduled flight to Philadelphia, officials said.

Police at the Detroit Metropolitan Airport twice had the man, in his 50s, blow into a breathalyzer, and each time his readings came back above the legal limit, said Michael Conway, a spokesman for the facility.

The Federal Aviation Administration, which prohibits pilots from flying with blood alcohol content higher than .04, said in a statement it was investigating the case.

Airport police did not give the pilot's name or the specific readings from his breathalyzer tests.

They released the Pennsylvania man from custody while they continued to investigate, Conway said, and will present evidence to prosecutors for possible charges.

Laura Nedbal, a spokeswoman for American Airlines, said the company considers the case a serious matter and was assisting local law enforcement and the FAA.

The co-pilot's flight 736, from Detroit to Philadelphia, was canceled and passengers were being accommodated on other flights, Nedbal said.

She declined to release further details, citing the pilot's privacy rights as an employee.