The Air New Zealand plane that lost cabin pressure and plunged thousands of feet is back flying passengers.
However, the cause of the incident on 30 August, during which passengers had to don oxygen masks, is still unknown.
Flight NZ414 was flying from Wellington to Auckland when pressure was lost and pilots dropped the plane more than 25,000 feet over just a few minutes.
The Transport Accident Investigation Commission says it has been an exhaustive process trying to find the problem.
Chief accidents investigator Tim Burfoot says some parts of the plane have been replaced and the original components are undergoing more testing.
Mr Burfoot says Air New Zealand flight-tested the plane before it was put back into service.