Aircraft Accident/Incident Report

Whittier, Alaska 99693
Saturday, September 22, 2007 14:20 AKD

The float-equipped airplane was departing from a remote lake as a pilot-witness watched its westerly takeoff run from the shoreline. The witness said that during the takeoff run, the nose appeared abnormally high as it lifted off, then "the wings began to wobble" as it disappeared behind an area of hilly, tree-covered terrain at the west end of the lake. The airplane subsequently collided with trees, which severed the right wing. It became inverted before colliding with an area of tundra-covered rock. The airplane's wreckage was about 800 feet from the west shoreline. During the NTSB's on scene investigation, the pilot's seat was found in the full aft position. There was no evidence of mechanical problems with the airplane's engine or flight controls during postaccident inspections. An FAA airworthiness directive (AD), 87-20-03 R2, defines the maximum acceptable wear limits on the seat locking mechanism and seat tracks. The AD states, in part: "...If the wear dimension across any hole exceeds 0.36 inches but does not exceed 0.42 inches, continue to measure each hole every 100 hours for excessive wear. ...If the wear dimension across any hole exceeds 0.42 inches, prior to further flight, replace the seat track." The NTSB IIC measured each of the 17 seat rail holes using a McFarlane seat rail wear gauge, revealing that 4 of the 17 holes were in excess of 0.42 inches. The 4 excessively worn holes were the 8th through 11th holes [from front to back]. Using an exemplar Cessna 180 and a pilot that was the same height as the accident pilot, it was discovered that the 9th seat track rail hole was selected after the seat was adjusted to comfortably operate the flight controls. Cessna issued service bulletin SEB07-5, which provides for the installation of a secondary seat stop kit for the pilot seat, free of charge. Compliance is mandatory within the next 200 hours of operation or 12 months, whichever occurs first. The bulletin was issued about 4 months before the accident, and the airplane had flown about 22.4 hours since its issuance. The accident airplane was not equipped with the secondary seat stop kit. Given the lack of mechanical deficiencies with the airplane's engine or flight controls, and the discovery of the worn seat rail holes, it is likely that the pilot's seat moved aft during the takeoff run, making it difficult for him to properly operate the airplane's controls.

The failure of the pilot's seat to engage, or remain engaged, and the pilot's inadvertent stall/mush during takeoff-initial climb. Contributing to the accident was the failure of maintenance personnel to comply with an FAA AD regarding the pilot's seat rails.