Accident Overview
On September 23, 2021, at approximately 1500 Pacific daylight time, a Hiller UH-12E helicopter, registration N5334V, sustained substantial damage in an accident near Bovill, Idaho. The aircraft was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot, the sole occupant, was not injured.
Pilot Report
The pilot reported that he had been applying dry fertilizer over trees under a timber company contract and had flown about 5.7 hours that day, refueling every hour. About 20 minutes after the last refueling, while on approach to the fertilizer service truck to refill the bucket, at approximately 40 ft above ground level and 20 ft from the truck, he felt a “sudden jolt,” and the helicopter “dropped” to the sloping terrain below. The pilot stated he had no time to react and that the helicopter did not yaw after the jolt. He recalled the torque gauge indicated between 85% and 90% at the time. After impact, the helicopter came to rest on its side, and the pilot noted that “everything” on the helicopter automatically shut down before he exited.
Witness Statement
A witness staffing the truck stated he did not hear anything abnormal regarding the engine and that the wind was light and variable at the time of the accident.
Maintenance History
Review of maintenance logbooks revealed that an annual inspection was accomplished on the day before the accident, and the engine was determined to be in an airworthy condition. At the time of inspection, the airframe had accumulated 21,096 total flight hours, and the engine had 15,415 total hours.
Postaccident Examination
Examination of the helicopter found that the cabin area and windshield structure were bent and distorted. The tailboom separated near the midsection, and the main rotor blades were buckled in multiple areas. No evidence of mechanical malfunctions or failures that would have precluded normal operation was found in the airframe or engine. The engine was shipped to the manufacturer for further examination, which confirmed fuel was present throughout the engine fuel system, including the spray nozzle. A test run demonstrated that the engine was capable of producing sufficient power.