Incident Description
During the takeoff roll, as the pilot powered the airplane for takeoff, his seat slid aft. He was unable to reach the controls to maintain control of the airplane. The airplane veered left off the runway surface and came to rest inverted after nosing over.
Examination Findings
Post-accident examination of the seat track revealed that the seat locking pin positively engaged in all of the seat track holes. However, the most forward hole contained a bolt used as a forward seat stop to prevent the seat from coming off the seat track. When the seat pin was engaged in this hole, full depth engagement was not possible. Rub marks were present on the bolt shank that was visible through the seat track hole. The pilot normally flew the airplane with the seat in its forwardmost position.
Maintenance Issues
The airplane manufacturer did not design the seat stop, and there was no installation record of the bolt used as a seat stop in the airplane maintenance records. The airplane was equipped with an after-market backup seat stop to prevent the seat from slipping aft if the primary seat locking mechanism failed. Although there were no mechanical problems noted with the device, the backup stop was not secured to the seat track.