A Japan Airlines co-pilot who was due to fly a passenger plane from London to Tokyo has been charged for being almost 10 times over the legal alcohol limit shortly before take-off.

Katsutoshi Jitsukawa will be sentenced later this month after pleading guilty at Uxbridge Magistrates Court in west London on Thursday to exceeding the alcohol limit.

The airline said the co-pilot was arrested on Sunday at Heathrow Airport for failing a breath test, causing a flight delay of one hour and 9 minutes.

Mr Jitsukawa cleared an earlier breath test, according to Japan Airlines.

The driver of a crew bus that was transporting him to the plane from Heathrow airport alerted police after smelling alcohol on him, Japan’s NHK public television said.

Tests found the 42-year-old first officer had 189 milligrams of alcohol per 100 millilitres of blood in his system, almost 10 times the 20mg limit for a pilot.

The limit for drivers in Britain is 80mg.

The airlines’ head of communications told reporters that it was “certain” the first breath test was not conducted properly.

Mr Jitsukawa acknowledged he had drunk about two bottles of wine and a pitcher of beer the previous night, NHK said.

He has been detained until his hearing on November 29.

Japan Airlines said the flight had to be operated by the remaining two pilots.

“The company sincerely apologises to the passengers and to all affected by the employee’s actions,” an airline representative told reporters.

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.

The last-minute sickie affected 619 passengers travelling from Japan’s southern Okinawa prefecture to smaller regional islands.

-with AAP