The Australian Transport Safety Bureau (ATSB) is investigating a Jetstar flight which flew lower than it was supposed to part way through its descent into Queenstown.
The incident happened on an Airbus A320 flight from Auckland to Queenstown on July 16.
"During descent, the crew had an incorrect descent profile selected and subsequently descended below the minimum safe altitude," the ATSB said.
Jetstar said the plane's pilots had reported that on approach an incorrect autopilot setting resulted in the aircraft going off its pre-determined track.
"This never put the aircraft in danger and the incident didn't trigger any cockpit alerts. The pilots realised the error and corrected it promptly. Even if the error had not been corrected, the aircraft would still have landed safely," Jetstar said.
The two pilots had a combined total of 23,000 hours experience and have been flying in-and-out of Queenstown for the past two years without incident.
A company spokesman said that for a short time when the plane was supposed to be at 7300 feet (2225 metres) it had dropped down to 6300 feet, and had then gone back up to 7300 feet.
The ATSB expects to have its investigation finished by November.