The Civil Aviation Authority has called for a report from the pilot of a helicopter that took off without him, at Tarras, on April 10.
CAA spokesman Matthew Shore told the Otago Daily Times the Robinson R22 helicopter had been "left unattended" with the engine running.
"It became airborne, spun around and struck the ground."
In the process, the helicopter's tail clipped the pilot on the back of the head.
The pilot was shocked but not injured, Mr Shore said.
The ODT understands the pilot was Dan Perriam, of Wanaka.
Mr Shore said the matter was regarded as a "relatively routine incident".
Most likely once the authority had seen the report and all questions had been answered, no further investigation would be required.
"We will get a full report from the operator and we will review it from there and see if we need to take any more action."
He would not provide the name of the pilot and could not say how much damage was done to the helicopter although it "nosed down and overturned".
Mr Shore said there had been "a couple" of similar incidents recently and it was "remarkably common".