Primary finding
Probable cause
The inadequate maintenance of the seat locking mechanism, which resulted in the pilot’s seat sliding back during takeoff and a subsequent loss of control.
Investigator assessment
Analysis narrative
During the takeoff roll the pilot’s seat suddenly slid backward, and she was unable to reach the pedals, which resulted in a loss of control and runway excursion. Examination of the airplane revealed substantial damage to the engine mount, fuselage, and horizontal stabilizer. The pilot’s seat tracks were a newer heat-treated version. There were wear marks on the seat lock pin tip indicative of previous alignment issues. The spring that held the lock pins in place was installed incorrectly and the corresponding push-pull rod was bent. This incorrect spring placement shortened the travel of the spring and reduced the tension on the lock pins. The seat brackets that attach to the spar exhibited worn and elongated bolt holes, which created a misalignment of the seat support. It’s likely that the condition of the seat locking mechanism prevented the seat from locking correctly, which resulted in the seat sliding back during takeoff. A review of the available airframe maintenance records did not reveal any entries regarding inspections or work performed on the seats or the seat tracks. The investigation was unable to determine when the pilot’s seat was last inspected, when the lock pin spring was incorrectly installed, and by whom.
Source record
Factual narrative
On July 11, 2024, about 1000 central daylight time, a Grumman AA-5B airplane, N23JK, was substantially damaged when it was involved in an accident near Camdenton, Missouri. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that before starting the engine, she adjusted her seat to the appropriate position to reach the flight controls, and then wiggled the seat to ensure it was secure. After taxiing to the runway, she wiggled her seat again and prepared for takeoff. During the takeoff roll her seat suddenly slid backward, and she was no longer able to reach the pedals. The airplane departed the side of the runway and came to rest upright in a ravine. Examination of the airplane revealed substantial damage to the engine mount, fuselage, and horizontal stabilizer. The pilot’s seat tracks were a newer heat-treated version. There were wear marks on the seat lock pin tip indicative of previous alignment issues. The spring that held the lock pins in place was installed incorrectly and the corresponding push-pull rod was bent. The seat brackets that attach to the spar exhibited worn and elongated bolt holes, which created a misalignment of the seat support. The most recent annual inspection was completed on January 8, 2024, at airframe total time of 4,423.7 hours. A review of the available airframe maintenance records did not reveal any entries regarding inspections or work performed on the seats or the seat tracks.