Incident
An aircraft crashed during thunderstorm activity after it was observed leaving a cloud in a steep dive. During the descent, a wing folded, leading to the crash.
Investigation
The investigation believed that the aircraft experienced inadvertent negative G forces while in the thunderstorm. This negative G loading likely caused the bottom wing strut bolt to shear, resulting in the wing no longer being correctly braced. The subsequent structural failure led to the wing folding and the crash.
It was noted that the US Military Beaver fleet had also experienced several similar fatal accidents under comparable circumstances, although no further details about those incidents were provided.
Possible Cause
The probable cause, as determined by the investigation, was the shearing of the bottom wing strut bolt due to inadvertent negative G forces encountered during thunderstorm activity, which led to the loss of wing bracing and structural failure.