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.