The Australian Transport Safety Bureau is investigating a Jetstar flight into Queenstown which descended below the safe level.
The incident happened last month.
During the descent of the Airbus A320 from Auckland into the South Island airport, "the crew had an incorrect descent profile selected and subsequently descended below the minimum safe altitude", the Australian Transport Safety Bureau said.
A report was expected to be completed by November, a spokeswoman said.
Jetstar, as an Australian company, falls under the jurisdiction of aviation authorities in that country.
In a statement Jetstar said an incorrect autopilot setting resulted in the plane going off its pre-determined track.
This never put the aircraft in danger and the error was picked up and quickly corrected, it said.