An on duty Ryanair steward drank whiskey from an aircraft's drinks trolley and a small bottle of wine, a court heard.
Sam Thompson, 26, from Cheshunt, in Hertfordshire, was working on a flight from Poland to Stansted Airport in May when a witness reported him.
He has admitted to performing an aviation function as a member of cabin crew while his ability to do so was impaired by drink.
He is due to be sentenced next month.
At a hearing on Monday, at Chelmsford Magistrates' Court heard Mr Thompson, of Warrenfield Close, was seen drinking Jack Daniels from the trolley before taking a small bottle of wine from his pocket and "necking the whole bottle".
The allegation relates to a flight from Rzeszow in Poland to Stansted Airport on 18 May.
Prosecutor Nishma Khan said police were called at around 18:10 BST after the witness saw him drink the whiskey before they "proceeded to film" him.
Police took a breath test from Mr Thompson at Stansted Airport, in Essex, where a reading of 50mcg of alcohol in 100ml of breath was recorded.
He then gave a lower reading of 39mcg at Harlow police station.
Ms Khan said the legal limit is 9mcg of alcohol per 100ml of breath, which is lower than the legal limit for driving of 35mcg of alcohol per 100ml of breath.
Defence solicitor Michael Carroll said the defendant and alcohol are "not the best of friends".
Magistrate Kristien Chafer ordered a pre-sentence report to be prepared on the defendant, exploring all sentencing options, including custody.
Mr Thompson has been bailed Thompson until his sentencing.