Air New Zealand is trying to determine what caused the windscreen of a passenger jet to crack, forcing the trans-Tasman flight to be diverted.
Flight NZ171 carrying 118 passengers, two pilots and four cabin crew left Auckland for Cairns on Sunday, but was forced to land in Brisbane after a windscreen on the left side of the plane cracked.
A passenger says the plane plummeted momentarily before diverting to Brisbane at a lower altitude and reduced speed.
Air New Zealand says the pilot followed standard operating procedure, descending gradually from about 34,000ft to about 23,000ft over a seven-minute period.
The airline says the crack developed in the cockpit window that is 4cm thick and made up of three panes of glass. It says only the inside pane was cracked, which in no way risked the whole windscreen.
The Australian Transport Safety Bureau says a crack in itself is not serious, and at this stage does not intend to investigate.
The bureau is waiting for a written report from the flight operator, which must be submitted within 72 hours of the incident.
Air New Zealand says a replacement windscreen has been fitted and the plane is back in service.
Passengers were flown to Cairns on Monday.