A witness reported that as the aircraft approached a ridge line about 5 kilometres from the DEPARTURE point he observed a marked "wing wobble". This was then seen to cease briefly, then recommence. Shortly afterwards, the aircraft collided with the top of the ridge line and cartwheeled down the slope before coming to rest against a tree. An inspection of the aircraft did not reveal any fault that may have contributed to the occurrence. At the time of the accident the wind velocity was north-westerly at about 15 knots and thus was blowing across the ridge struck by the aircraft. It is likely that the aircraft, while being flown at a low altitude, was affected by mechanical turbulence in the lee of the ridge line and collided with the ground.
