What happened
During a banner towing operation, the pilot attempted the first tow of the day. Upon deploying the tow hook—a grappling hook attached to a rope—the tow line became entangled in the rudder controls, interfering with the movement of the rudder bell crank. As the aircraft captured the banner, the weight of the banner placed significant tension on the tow hook line. This tension prevented the use of the aircraft's hook release mechanism and caused the rudder to deflect. Consequently, the aircraft entered a stall and spin, resulting in impact with the ground.
The investigation
The investigation examined the interaction between the tow line and the aircraft's control surfaces. Evidence showed that the weight of the captured banner created enough tension on the line to preclude its release via the existing STC-installed hook release mechanism. Additionally, the investigation noted that according to FAA Circular AC 43.13-2A, the system should have been tested to ensure no interference existed with the tailwheel or adjacent structures. Personnel from the operating company noted that the pilot failed to visually verify that the line was clear of the rudder bell crank after deployment and proceeded with the tow rather than landing to clear the entanglement.