The Civil Aviation Authority (CAA) has ruled out engine failure as the cause of a plane crash in the Ruahine ranges on Monday.
The authority says the engine of the light plane was still producing power when it crashed.
The CAA says it is now looking at other possible causes.
Flying instructor Gary Skedgwell, 30, is in critical condition after surgery in Wellington hospital. He has head and leg injuries.
Trainee pilot Samual Metzger, 18, is in a stable condition in Palmerston North hospital. He has chest and leg injuries.