Incident Details
On July 26, 2012, about 1630 central daylight time, an American Champion Aircraft model 8KCAB airplane, N60GK, experienced seat tubing separation during an air show maneuver over Wittman Regional Airport (OSH), near Oshkosh, Wisconsin. The airline transport pilot, the sole occupant, was uninjured, and the airplane sustained no damage. The airplane’s registration to the pilot was pending, and the pilot operated the aircraft under 14 Code of Federal Regulations Part 91 as an air show flight. Visual flight rules (VFR) conditions prevailed, and the flight was not operated on a VFR flight plan. The local flight originated from OSH about 1625.
According to the pilot’s incident report, he was cleared into the air show box. He performed a roll on takeoff followed by a half Cuban eight, four-point roll, hammerhead, and a one-and-a-half roll to an inverted turn-out/climb away from the crowd. The pilot climbed to 1,300 feet above ground level and entered the aerobatic box from the south with a 45-degree descending roll. At 150 mph he pulled into a 4g loop and initiated a snap-on-top-a-loop at the 60-degree inverted climb point. At that time, the seat broke, immediately laying the pilot back onto the rear seat and rear control stick. The rear controls were temporarily jammed by the pilot and the broken seat back. The airplane recovered by itself after one and a half rolls to the right-side-up position with wings level. The pilot established level flight away from the crowd, assessed the situation, and once confident of control, requested landing clearance from the air boss, landing on runway 36L without incident.
Investigation Findings
Federal Aviation Administration (FAA) inspectors examined the incident airplane and found that the seat bottom frame had separated. Additionally, the seat bottom frame, serial number A02443, was not equipped with a reinforcement truss. The manufacturer reported that the incident adjustable seat assembly part number was 7-1499, revision K. The bottom and back adjustable seat sub-assembly frame part number was 7-1513, revision D. The seat bottom sub-assembly was missing its reinforcement truss, a welded stiffener with part number 2-2166, revision C.
The manufacturer reviewed production work orders and discovered that a batch of 10 seats had been produced that were not constructed with the stiffener and were non-conforming in reference to the production type certificate. The non-conforming batch of seats were marked with serial numbers A02437 through A02446. The manufacturer identified affected stock seats and which other airplanes were affected by the installation of non-conforming seats.
Manufacturer Response
The manufacturer made arrangements for the return of all installed non-conforming seats. According to the manufacturer, the nine remaining seats would be reworked by welding on the reinforcement truss stiffener. With the stiffener in place, the seat bottom frame conforms to the type certificate design. The manufacturer further indicated that steps were added to the paperwork for seat production to ensure assemblers pull all the parts when making a batch of seat assemblies. Inspection had the same type of step added to their paperwork. Another change in manufacturing was that the seat welding fixture now has a locater for the reinforcement truss stiffener parts, serving as a visual cue in addition to the paperwork. The manufacturer believed that this visual cue would reduce complacency regarding memorized paperwork associated with repetitive assembly operations.
Service Letter 437 was published, indicating that owners should conduct a one-time inspection of the folding front seat bottom to ensure that the seat bottom frame contains the required 2-2166 reinforcement truss. In follow-up communications with a manufacturer’s representative in March 2013, he reported that the nine remaining seats had been reworked and conformed with the type certificate. Additionally, by that time, the improved assembly and inspection paperwork and welding fixture locators had been implemented.