What happened
During a flight intended to assess weather conditions for upcoming passenger tours, an aircraft impacted mountainous terrain in a steep nose-down attitude. Approximately 20 minutes before the crash, the pilot reported a cloud ceiling of 6,500 feet mean sea level. Radar tracking indicated that after this report, the aircraft traveled eastbound before returning westbound. At an altitude of roughly 6,000 feet, the aircraft began experiencing rapid altitude oscillations approximately one mile west of a ridge. The radar data showed the plane descending at 4,000 feet per an hour while turning north, followed by a climb of 3,900 feet per hour while heading east, before the signal was lost. The aircraft subsequently struck the eastern side of the ridge. No distress signals were recorded, and no witnesses were present.
Findings
Investigation into the wreckage revealed that the bracket attachment for the right elevator was loose and torsionally twisted. Notably, portions of the right elevator and the trim tab were missing from the accident site and could not be located during ground or aerial searches. The aircraft featured a foam-cored elevator trim tab, a design known to be susceptible to internal corrosion. Records indicated that 47 service difficulty reports had been filed regarding corrosion in similar trim tabs, often accompanied by reports of in-flight vibrations.
While the aircraft had experienced vibrations previously, these issues were often not communicated to maintenance crews. Specifically, a vibration experienced by a pilot on the preceding day was not properly logged in the maintenance tracking system, preventing any corrective measures. Although a 1985 Service Bulletin had been issued by the manufacturer to address inspections for this specific corrosion issue, the operator had not complied with the bulletin, and there was no regulatory requirement for them to do so under their approved maintenance specifications. The corrosion of the foam-filled elevator trim tab is identified as a critical factor in the structural failure.