What happened
During the takeoff roll, the pilot's seat unexpectedly slid toward the rear of the cockpit. This movement prevented the pilot from reaching the controls necessary to maintain directional control of the aircraft. As a result, the airplane veered left off the runway surface and came to rest in an inverted position. There were no injuries reported.
The investigation
An examination of the seat track following the accident revealed that the seat locking pin had positively engaged with all available holes in the track. However, a bolt had been installed in the most forward hole to serve as a seat stop, preventing the seat from sliding too far forward. Because of this bolt, the seat pin could not achieve full depth engagement in that specific hole. Physical evidence, including rub marks on the bolt shank visible through the track hole, indicated movement had occurred.
While the pilot typically operated the aircraft with the seat in the most forward position, investigation showed the manufacturer did not design this specific seat stop, and maintenance records contained no installation history for the bolt. Additionally, although the aircraft was equipped with an aftermarket backup seat stop intended to prevent rearward sliding in the event of a primary mechanism failure, this device was not secured to the seat track.