The tipsy copilot, identified as Katsutoshi Jitsukawa, was arrested Sunday at London's Heathrow Airport after a test administered just 50 minutes before takeoff revealed the level of alcohol in his system, the BBC reports.
The Japan Airlines plane was delayed and took off 69 minutes after its scheduled departure from London.
He was caught after the driver of a crew bus smelled alcohol and called the police, according to Japanese broadcaster NHK.
The pilot pleaded guilty to drunk in the municipal court of Uxbridge on Thursday.
It was found that his body contains 189 mg of alcohol per 100 ml of blood, although the allowable limit for pilots of 20 milligrams.
A Japan Airlines pilot who was arrested in Britain shortly before a flight for being drunk was nearly 10 times over the legal blood alcohol limit for a pilot, London police said.
The limit for drivers in Britain is 80mg.
Two planes collide MID-AIR over Canada
Police walk on to a property as they work at the site of a small plane crash in the Carp area of Ottawa on November 4, 2018. Investigators will be taking the Cessna to their laboratory in Ottawa to help determine the cause of the accident.
The co-pilot acknowledged he drank about two bottles of wine and a pitcher of beer the previous night, NHK said.
Sentencing for the pilot is set for November 29. The flight took off more than an hour late.
"The company sincerely apologises to the passengers and to all affected by the employee's actions", JAL said in a press release.
The almost 12-hour flight from London to Tokyo normally has two captains and a co-pilot.
"We will implement immediate actions to prevent any future occurrence and to regain our customer's trust".
The apology came a day after another major Japanese airline, All Nippon Airways, apologised for causing delays to five domestic flights after a pilot became unwell due to heavy drinking the night before.