Air New Zealand crew failed to follow emergency procedure when a domestic flight lost cabin pressure, the Transport Accident Investigation Commission has found.
The plane from Wellington was descending to Auckland in August 2013, when emergency oxygen equipment was deployed.
The commission released its findings on the incident today, but said it was not able to identify the cause of the low pressure.
It found the pilot did not warn the cabin crew of an emergency descent, and the passenger oxygen switch was not turned on.
It said two cabin crew members also delayed fitting their masks, which could have led to loss of consciousness.
The senior flight attendant had a mask on, but did not know it was not operating because of lack of training.
The commission said Air New Zealand had since addressed the problems.