Hong Kong airline Cathay Pacific says it is investigating claims a couple travelling first class from Toronto used the crew rest area in a Boeing 777 to join the "mile-high club".
A purser allegedly invited the couple to use the off-limits area to have sex when he saw them getting intimate in their seats that fold out into beds in the new-style first class cabin.
The passenger, an American doctor in his 20s, posted pictures on a blog of himself lying on the bunk - used by pilots to rest between shifts on long-haul flights - as evidence of what he calls his "amorous adventure."
The unnamed passenger, who has posted several previous blogs describing his front-end flying experiences, says the visit to the rest area on board the Cathay 777-300ER was made possible by a purser called Alvin who he knew from previous flights.
Three other people were in he first class compartment on the flight and the passenger wrote on his blog: "On these long, long flights there isn't really anything to do after the meal service so my gf (girlfriend) and I were cuddling and watching movies.
"With the magnificent large bed one thing led to another and soon my friend Alvin was at our side saying would you like the privacy of our crew rest upstairs? It is currently unoccupied..."
Two photographs which appear to have been taken by his girlfriend show the suited blogger - with his face deliberately obscured - sitting in the seat in front of the crew bunk and lying down on one of the bunks, which has ruffled sheets and blankets.
"I felt like a celebrity," he wrote on his blog which also features pictures of the First Class bathroom, the pilots in the cockpit and every plate of food served up the flight which costs more than 4000 pounds sterling for a one-way ticket.
Cathay Pacific said it was examining the blog, posted earlier this month, to see if the purser broke the rules by allowing passengers into the crew rest area.
An airline spokeswoman said, "We are looking into the case. It is a company's policy that the cabin crew and cockpit crew rest bunks can only be used by operating crew and not for any staff or passengers."
Pilots reacted with surprise to the claims with one Hong Kong pilot writing on the www.airliners.net website where the blog was posted: "I have seen the crew rest area opened to a very ill and sick passenger but never for a passenger - even in First Class - just because he was getting frisky in the cabin."
A senior Cathay Pacific pilot, speaking on condition of anonymity, said, "I frankly think it's unlikely this really happened.
"On a flight from Toronto there will be someone in the cockpit crew rest area almost all the time. There are four pilots and two will be in there at a time apart from the breaks between shifts which will only be about 15 minutes."