Japan Airlines says one of its pilots was detained by London police last month. He was found to be under the influence of alcohol just before he was about to pilot a flight to Tokyo.
The airline apologized for the incident at a news conference in Tokyo on Thursday.
The 42-year-old copilot was taking a bus from a terminal at London's Heathrow Airport to the tarmac on Sunday when the driver noticed that he smelled of alcohol.
Police found 0.93 milligrams of alcohol per liter of breath, or more than 10 times the legal limit under the UK's Aviation Law. The police took him into custody for questioning.
The flight bound for Tokyo's Haneda Airport was scheduled to have 3 pilots in the cockpit, but took off an hour late without the copilot.
The copilot admitted to airline officials that he had drunk more than 1.5 liters of wine and more than 1.8 liters of beer in a hotel bar and in his room the night before.
But Japan Airlines said its preflight test did not detect alcohol on his breath. JAL officials said they suspect that the copilot rigged the test to mask his drinking. They said they will change their testing method to prevent fraud.
In a separate case last week, the captain of a Japanese domestic flight missed his flight because he was too hung over to work. He had violated his airline's ban on drinking alcohol within 12 hours of a flight.