NTSB Probable Cause

A LOSS OF AIRPLANE CONTROL INITIATED BY INADVERTENT CONTROL INTERFERENCE BY THE PASSENGER PILOT WHILE APPARENTLY ATTEMPTING TO QUELL A DISTURBANCE OF AN UNKNOWN NATURE. AS A RESULT, THE PILOT DID NOT, OR WAS UNABLE TO, MAINTAIN SUFFICIENT CONTROL OF THE AIRPLANE TO PREVENT A STALL/SPIN. A FACTOR WHICH CONTRIBUTED TO THE ACCIDENT WAS THE DARK NIGHT CONDITION.