In most circumstances, it’s the law of the nation where the airplane is signed up that applies on board. Therefore, a United States traveler aged 18 travelling aboard a Qantas airplane in US airspace can lawfully consume alcohol, although US law specifies a minimum legal age of 21. Nevertheless, there are abnormalities. A traveler found to be in ownership of controlled substances on a Singapore Airlines flight from Singapore to Frankfurt would be prosecuted under mahanyertl, not Singapore’s.
Likewise, if an offence takes place while the airplane is on the ground, local laws bypass the laws of the nation of registration. That’s what took place to Pakistan International Airlines’ Captain Irfan Faiz, who was found to be 3 times over the United Kingdom’s legal blood-alcohol limitation for pilots before he removed from Leeds Airport.
Although his airplane was signed up in Pakistan, and he would have been allowed to fly under that nation’s air travel laws since he was not in offense of their 12 hour “bottle-to-throttle” requirement for pilots, he was condemned under British law and invested 11 months as a visitor of Her Majesty.