What happened
During the landing roll of an agricultural airplane, the aircraft departed the right side of the runway and entered soft terrain. The momentum caused the aircraft to nose over into an inverted position.
The pilot reported that during the landing roll, his seat became dislubricated from the seat track. Because the pilot's left leg is shorter than his right leg, the rearward movement of the seat caused his left foot to lose contact with the rudder pedal.
The investigation
An FAA inspector examined the seat and found that the forward left seat roller housing assembly had spread open to nearly the width of the seat rail. This condition allowed the seat to dislodge from its locked position.
While maintenance records indicated that AD 87-20-03 R2—a directive intended to ensure proper engagement of the seat locking mechanism and prevent inadvertent slippage—had been performed during the last annual inspection, the inspector determined the AD had not been properly accomplished. The examination revealed the seat did not meet the required locking pin engagement standards. At the time of the accident, 249.4 hours had elapsed since the last annual inspection.