What happened
The pilot was performing a landing on a frozen lake in a wheel/ski equipped airplane to wait for weather conditions to improve. During the landing roll, the pilot heard a "whump" sound, after which the aircraft settled onto its left wing.
The investigation
Post-accident inspection of the aircraft revealed that the main landing gear attaching bolt had suffered an overload fracture across a threaded area. Investigators determined that the installed NAS-147R bolt was not the correct part specified for the installation. This NAS-147R bolt featured a shorter smooth shank section of 1.3 inches, whereas the required AN bolt required a 1.43-inch smooth shank. Because of this discrepancy, when the NAS-147R bolt is installed in the landing gear, a portion of the threaded area remains inside the bolt hole. Records indicated that this bolt had been installed three weeks before the accident during the aircraft's most recent annual inspection.