One of three pilots on Flight 55 to Chicago had been arrested before the flight boarded on suspicion of being intoxicated, airline spokesman Tim Wagner said.
Greater Manchester Police confirmed that a crew member, a 45-year-old man from Ohio, had been arrested. He was released on bail pending the results of tests and was due to report to a Manchester police station Tuesday, a police spokesman said.
The flight, scheduled to depart at 10:30 a.m. local time, left the northwestern English city about an hour late and was due to stop in New York to pick up a new pilot before continuing to Chicago. Three pilots are required on flights lasting longer than eight hours.
The plane was expected to land in Chicago at 3:50 p.m. CST.
Wagner said the airline had begin an internal investigation into the arrest, which he called an "isolated incident."
There have been a number of cases of pilots and co-pilots being arrested for allegedly trying to fly planes while drunk.
In 2002, a drunk America West pilot and co-pilot were arrested at Miami International Airport as they boarded a flight. A judge sentenced them in July to prison terms of five years and 2 1/2 years, respectively.
A pilot with the Finnish national airline Finnair was jailed for six months after an August 2004 incident in which he tried to fly a packed passenger jet drunk. When he was arrested, he had almost 2 1/2 times the legal limit of alcohol in his blood, prosecutors said.
In June, a Norwegian court sentenced the pilot of a British Airways jet to six months in prison for preparing to fly in November 2003 even though his co-pilot and members of his crew were drunk.
In October, a United Airlines pilot was removed from the cockpit and questioned by police in October after security screeners at Miami's airport reported smelling alcohol. The pilot was not arrested and no breath test was done, but the airline suspended him pending an ongoing internal investigation.