Air New Zealand says one of its pilots fell into a deep sleep while at the controls of an international flight but insisted safety aboard the aircraft was never compromised.

He was one of two pilots flying a 332-seat Boeing 777-300ER from London to Los Angeles in November 2011, according to a report released after a freedom of information request.

The Civil Aviation Authority (CAA) document said the pilot voluntarily submitted a "fatigue report" with the regulator, recounting how he slept on the job.

The pilot, who was not identified, blamed a poor night's rest in London, when air-conditioning problems in his hotel meant he had to change rooms three times, for his exhausted state on the flight.

"I suddenly, and without any warning, fell into a deep sleep on the flight deck. The same event occurred twice," he said.

Air New Zealand said safety was paramount for the airline and it encouraged staff to report instances of fatigue as part of a program to manage shift rosters to address the issue.

It said the flight in question had three pilots aboard.

"During the cruise phase of the flight, one of the two operating pilots nodded off twice for around a minute and woke spontaneously," it said in a statement.

"The other operating pilot on the flight deck was aware of this and safety was not compromised at any point."

Air New Zealand said the pilot would not face disciplinary action as it did not want to discourage staff from reporting such incidents.

AFP