The Australian Transport Safety Bureau is investigating the landing of an Air New Zealand flight in Brisbane earlier this month.
The flight reportedly descended "below the radar lowest safe altitude" which the ATSB considers an 'incident'.
The aircraft involved was ZK-OKN, a Boeing 777-300 owned by Air New Zealand. The landing took place at Brisbane Airport on 18 November.
A preliminary report from the ATSB says: "The flight crew were cleared to descend to 3,000 ft. Shortly after the aircraft was observed to have descended to 2,500 ft. The flight crew were alerted to the error, but the aircraft continued descent to about 2,000 ft."
The investigation will involve reviewing flight data and interviewing the flight crew on board. It’s expected to be completed by April 2018.
Air New Zealand has been approached for comment.