Unknown

In the light of the investigation, the cause of this accident was considered to be unknown, and was, therefore, classified as "undetermined". However, the reasons which may have caused the aircraft to enter a spin are listed hereunder: One probable cause was a failure of the suction pump or the vacuum system. If the vacuum system had failed the artificial horizon, directional gyro and turn-and-bank indicator would have become inoperative. A failure of this sort, aggravated by turbulence, would deprive the pilot of the means to control the aircraft which, in these conditions, might have stalled one or more times. Another cause which might have produced a spin was flying into very severe turbulence with loss of control leading to a stall. Engine failure was not considered probable, although a malfunctioning of one of the propellers was not ruled out. It was considered that the pilot would have alerted the tower if an emergency has occurred, whereas it was considered unlikely that he would have done so if the instruments failed or if he encountered severe turbulence, as in these circumstances his entire attention would have been concentrated on trying to restore the aircraft to a normal attitude.