Long-haul flights are a rare situation in which it appears to be socially acceptable to day-drink. It's been part of the culture since the golden days of flying. But how many drinks is "reasonable"?
Is there a set limit on the number allowed?
No. Technically, on most airlines at least, it's an open bar that's there for (almost) the duration of the flight. "Alcohol is included and can be requested at any time when the drinks service is open," a spokesman for Air France told us. "As long as the customer is not disturbing other passengers or engaging in anti-social behaviour, this service is available." The sentiment was echoed by BA, Virgin Atlantic and Lufthansa.
So, how many drinks is acceptable?
A survey of our Travel department aroused varying responses: "Four or five: a few beers, a couple of glasses of wine and a whisky," said one. More sensibly, three of our travel experts don't drink at all on flights - but one makes sure he pockets a mini wine bottle or two, to use in cooking back home.
Why is free alcohol served?
The simple answer is that putting up a booze paywall on lengthy flights just wouldn't be tolerated. Look what happened when United Airlines attempted to do away with tomato juice: it triggered an uproar and they quickly performed a U-turn.
Can I ask for a Bloody Mary at breakfast?
According to former BA flight attendant Andy Sparrow, it's the most irritating drink to prepare: "That was the order we dreaded. It takes an age to sort out all the trimmings, and it's infectious. As soon as one person asks for one, half the cabin fancy their own."
How do the cabin crew judge your intoxication levels?
The same way anyone would: slurring, swaying and giggling all being red flags. But also, according to one, they watch for passengers who go to the bathroom more often than normal, or who switch between galleys when they ask for more, assuming the staff at both don't share notes.
Does altitude have an effect?
Dr Nick Knight, a GP registrar with a special interest in sports, exercise and lifestyle medicine, explains: "At cruising altitude, most cabins are pressurised to the equivalent of 6000ft to 8000ft above sea level. Under such conditions, less oxygen will be taken up into your bloodstream compared with if you were at sea level. The knock-on effect of this is that your brain may experience a very mild reduction in the amount of oxygen it is used to. This is called 'hypoxia' and is more likely to give you that sensation of being more drunk."
What are the licensing laws?
There are none. Airlines can make their own rules, which usually mirror the country in which they are based. So United, being an American airline, doesn't allow drinking under the age of 21. For British Airways, the age limit is 18. And many Arab airlines don't serve alcohol at all. A Qantas spokesperson told us, "Our crew will always ensure any alcohol is only served to those over 18 years of age. Every crew member must also have a Responsible Service of Alcohol (RSA) certificate."
- Telegraph Media Group