What happened
During a departure from a remote lake, a pilot-witness observed a Cessna 180 performing a westerly takeoff run. As the aircraft lifted off, the nose appeared abnormally high. The witness reported that the wings began to wobble as the aircraft moved behind hilly, tree-covered terrain at the west end of the lake. The airplane subsequently struck trees, which severed the right wing. Following this impact, the aircraft became inverted and collided with tundra-covered rock. The wreckage was located approximately 800 feet from the west shoreline. There were no fatalities reported.
The investigation
During the on-scene investigation, investigators found the pilot's seat in the full aft position. Post-accident inspections of the engine and flight controls revealed no evidence of mechanical problems. However, an examination of the seat locking mechanism and tracks was conducted in relation to FAA airworthiness directive 87-20-03 R2, which defines maximum acceptable wear limits. Using a specialized gauge, the NTSB IIC measured all 17 seat rail holes and discovered that 4 of the 17 holes exceeded the 0.42-inch limit. These worn holes were located from the 8th through the 11th position from the front.
Testing conducted with an exemplar Cessna 180 and a pilot of similar height to the accident pilot revealed that the 9th seat track rail hole was selected after adjusting the seat for comfortable control operation. Although Cessna had issued service bulletin SEB07-5 to install a secondary seat stop kit, the aircraft was not equipped with this kit at the time of the accident.