It is amazing how this can happen, especially on an international flight. The pilots have 24 hours at a minimum layover, enough time to have some drinks and sober up. But another idiot  is risking his 200,000 dollar a year job(edited: It was brought to my attention that American Pilots took a 40% pay caut in March of 2002, and my estimate of their pay rate was grossly exagerated. Apologies) by showing up at the airport  intoxicated.

An American Airlines pilot was arrested in Britain on Saturday on suspicion of being drunk before a scheduled flight to Chicago, the airline said.
A statement by the world’s No. 1 airline said the crew member was a relief pilot on the Boeing 767-300 with 198 passengers, meaning he was a backup to the captain and first officer. The crew member was not identified.
He was arrested on suspicion of being under the influence of alcohol after reporting for duty at Manchester airport, the carrier said. A court appearance was scheduled for Monday.
American said in a statement it was investigating and would not provide additional details. via  Reuters.com.