Jitsukawa was found to have 189mg of alcohol per 100ml of his blood - surpassing the legal alcohol limit of 20mg for pilots nearly ten times.
Tests found the 42-year-old first officer had 189 milligrams of alcohol per 100 millilitres of blood in his system, nearly 10 times the 20mg limit for a pilot.
JAL said the level of alcohol in the 42-year-old co-pilot's system sharply exceeded the legal limit in Britain after drinking two bottles of wine and five cans of beer for six hours from 6pm the night before the flight to Haneda airport.
Just 50 minutes before a flight from London to Japan was scheduled to depart, the pilot was arrested for having nearly 10 times the legal amount of alcohol allowed in his system.
Japan's Transport Ministry on Thursday issued a document directing all Japanese airlines to report by month-end measures being taken to control drinking by flight staff.
For road drivers in England, Wales and Northern Ireland, the drink-drive limit is 80mg. He will be sentenced at Isleworth Crown Court on November 29.
A Japanese pilot, who was on his way to fly a plane out of Heathrow Airport, has admitted to being drunk.
And not just drunk, he was 10 times over the permissible alcohol limit for pilots.
JAL's company rules prohibit its pilots from drinking alcohol less than 12 hours before flying any planes.
'We are certain (the in-house breath test) wasn't conducted properly, ' Muneaki Kitahara, JAL's head of communications, told a press conference.
It apologised on Thursday for the incident.
Due to the arrest, the flight's departure for Haneda, scheduled for 7 p.m. Sunday local time, was delayed by 1 hour and 9 minutes.
The male pilot in his 40s called in sick after a night of drinking on the remote resort island of Ishigaki in southern Okinawa prefecture, the company said.