A helicopter probably crashed into Bluff Harbour because the student pilot made a mistake in a low-speed manoeuvre, an investigation has found.
Instructor Jason Wright, 29, of Bluff, and his pupil Allan Munro, 67, of Avondale, 75km north of Invercargill, were killed when their Robinson R22 crashed in the harbour in October, 2010.
The Civil Aviation Authority (CAA) report into the crash was released on Tuesday.
It found the engine was not producing power and the rotors were not turning when the helicopter hit the water at such a speed no one could have survived.
It said Mr Munro, who had bought the helicopter the year before, probably did not know enough about the helicopter's reaction to low rotor speed and may have mishandled the entry into an autorotation - where the rotors are spun by the air passing through them rather than the engine.
He may have reacted as if flying an aeroplane and it was likely Mr Wright did not have time to intervene before it was too late.
The CAA did not make any safety recommendations.
NZN