It is still not clear what caused an Air New Zealand plane to lose cabin pressure, forcing more than 80 passengers and crew to don oxygen masks.
Five crew members and 76 passengers were on board Flight 414 from Wellington to Auckland on Friday when the pilots had to take emergency action.
They were forced to plunge the plane more than 25,000 feet over a few minutes.
The plane landed in Auckland without any further incident.
Transport Accident Investigation Commission staff are looking at the Boeing 737-300 again.
TAIC chief accidents investigator Tim Burfoot says the problem could be an intermittent one, which would make it harder to find.