A glider that crashed in Blenheim in 2009, killing the pilot, is likely to have been brought down by turbulence and downdraughts.
The 55-year-old pilot died when the aircraft hit the side of a steep hill, nose first.
The Civil Aviation Authority's investigation could not determine the cause of the crash, but its report does not attribute it to mechancial failure.
The report indicates the pilot had to navigate in winds of up 30 knots before the crash and that turbulence at the time is likely to have been severe.
The CAA says the accident serves as a reminder to the gliding community to ensure conditions will be good before taking off on flights.