Once you are on the airport, in uniform with the intention of flying and your name is on the crew manifest you are fair game for a violation.
And in recent years, the absolute best place for an American pilot to blow over the limit without getting jail time is Heathrow:
No jail for US pilot caught in plane over alcohol limit
A US pilot who was over the alcohol limit as he prepared to take off from Heathrow Airport has been given a 10-month suspended jail sentence.
BBC News - No jail for US pilot caught in plane over alcohol limit
Heathrow pilot caught drunk at 9am about to fly to America is spared jail
A pilot who was three times over the alcohol limit in the cockpit of a Boeing 747 at Heathrow was spared jail yesterday after pleas from his bosses.
Heathrow pilot was caught drunk at 9am about to fly to America | Daily Mail Online
Captain Joseph C******, 57, said the unfamiliar tipple was stronger than alcoholic beverages he usually drank and he did not realise it would put him over the limit when he turned up at Heathrow the next morning.
..."One doesn't know how that alcohol will affect someone if something unexpected happens. As you ought to know, it could have catastrophic results.
"For that reason the courts always take a dim view of this offence. Usually the sentence is one of imprisonment."
The judge said because of his distinguished track record and glowing references from colleagues, he would instead impose a fine of £1,500, with £300 costs.
American pilot blames 'British beer' - Telegraph