Event Description
The pilot initiated the takeoff roll. As the airplane accelerated, the pilot's seat slid back to its aftmost limit. Consequently, the airplane departed the runway, impacted bushes, and sustained substantial damage.
Investigation Findings
A review of the airplane's maintenance logbooks revealed that a new set of seat rails had been installed approximately 31 flight hours before the accident. Examination of the seat rails showed that the inboard rail had been modified with the addition of five locking pin holes.
The airplane was originally equipped with a single locking pin type seat. However, a dual locking pin type seat had been installed. Selection of any seat position other than the three most aft positions resulted in partial engagement of a single locking pin, while the other locking pin rested on top of the opposite seat rail. This combination of seat and seat rails was improper.