He was removed from the cockpit in handcuffs after some passengers had already boarded.
Monaghan was sentenced to eight months in prison at Lewes Crown Court yesterday.
After he was arrested aboard the jet due to take off at 8.20pm police found a reading of 86mg of alcohol per 100mg of blood.
Julian Monaghan, who worked for British Airways, went to work with a blood alcohol level far above the legal limit and has now been jailed.
The night before, Monaghan had been on an overnight flight from Cape Town to Heathrow, during which he drank a glass of red wine.
Pilots must follow a strict "bottle to throttle" policy forbidding them from drinking eight hours before a flight.
Mr Monoghan had drank three miniature bottles of vodka with a Pepsi in his hotel room on an empty stomach, before heading to the airport, it was heard in court. "The lives of the people on board are in the hands of the pilot‚" she told Monaghan.
He had worked for British Airways for 17 years and has resigned. He had not eaten and barely slept.
Amy Packham, prosecuting, said the reading taken at 22:30 GMT remained so high that he must have drunk a "significant amount" just before the eight-hour limit.
His childhood dream was to be a pilot and he was "proud and delighted" to work for BA, where he was "well-liked" and "trusted" by colleagues.
But he had been "extremely stupid" and bitterly regretted his actions, and wanted to apologise to the court, the public, passengers and his family, Mr Jones said.
He added: "He didn't knowingly arrive at work over the limit".
"Certainly he will never fly as a commercial pilot again". He appears before your honour as a shadow of the man he once was.
Mr Jones said Monaghan's "career and livelihood and personal and professional reputation are all up in smoke".
Emlyn Jones, defending, said Monaghan, "was not falling down drunk, making mistakes, being rude, picking fights".
Det Con Stuart Macpherson, of Sussex Police, said: "Had Monaghan been required to take control of the aircraft in the event of an emergency on the flight deck in the early stages of the flight, his judgement and abilities would have been impaired".