Air New Zealand has said that one of its pilots fell into a deep sleep twice while at the controls of a passenger flight between London and Los Angeles.
The airline said the incident happened on a Boeing 777 flight between London and LA in 2011.
The pilot, who has not been named, is reported to have said he fell asleep twice during the flight after not being able to rest properly because London hotel rooms were either "too hot or too cold".
The airline has insisted that safety was not compromised during the flight as the pilot was not alone at the cockpit's flight deck at the time.
According to the New Zealand Herald the pilot has the backing of the Air Line Pilots' Association, which said the incident showed the importance of air crew being "provided with quality hotel rest".
Speaking to the New Zealand television channel 3 News, Transport Minister Gerry Brownlee called on Air New Zealand to prove its safety standards: "You need to satisfy the public you're making sure your pilots aren't asleep on the job. You've got big reputation issues here; this doesn't look good."
An airline spokeswoman told the New Zealand Herald that a second pilot on the flight deck was aware his colleague had fallen asleep and "safety was not compromised at any point".
She said the pilot had "nodded off twice for around a minute and woke spontaneously".
Local media reports said details only emerged after a request was made under the official information act.
In a statement quoted by the New Zealand Herald, Air New Zealand said: "During the cruise phase of the flight one of the two operating pilots nodded off twice for around a minute and woke spontaneously."
"The other operating pilot on the flight deck was aware of this and safety was not compromised at any point."