WPR21LA354

The helicopter was performing an aerial application flight. While approaching the fertilizer service truck to refill the bucket, the pilot felt a “sudden jolt,” and the helicopter lost altitude. The pilot was unable to regain control, and the helicopter did not yaw after the jolt. The helicopter subsequently impacted the terrain below. The helicopter sustained substantial damage to its main rotor blades and fuselage. Before the pilot could exit the helicopter, “everything” on the helicopter, including the engine, automatically shut down. Postaccident examination of the wreckage, including the engine, revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Also, the examination yielded no evidence to explain why the engine automatically shut down after the accident. As a result, the reason for the pilot’s loss of helicopter control could not be determined based on the available evidence for this accident investigation.

On September 23, 2021, about 1500 Pacific daylight time, a Hiller UH-12E helicopter, N5334V, was substantially damaged when it was involved in an accident near Bovill, Idaho. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot reported that he had been applying dry fertilizer over trees as part of a timber company contract and had flown about 5.7 hours that day. The pilot also reported that he refueled the helicopter every hour. About 20 minutes after the last refueling, the pilot was on approach to the fertilizer service truck to refill the bucket. About 40 ft above ground level and about 20 ft from the truck, the pilot felt a “sudden jolt,” and the helicopter “dropped” to the sloping terrain below. The pilot stated that he had no time to react and that the helicopter did not yaw after the jolt. He recalled that the torque gauge indicated between 85% and 90% at the time. The helicopter impacted the ground and came to rest on its side. The pilot further stated that “everything” on the helicopter automatically shut down before he exited. A witness, who was staffing the truck, stated that he did not hear anything abnormal regarding the engine. The witness also stated that the wind was light and variable at the time of the accident. Review of the maintenance logbooks revealed that an annual inspection was accomplished on the day before the accident and that the engine was determined to be in an airworthy condition. At the time of the inspection, the airframe had a total time of 21,096 hours, and the engine had a total time of 15,415 hours of total time. Postaccident 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. The examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The engine was shipped to the manufacturer for further examination, which found that fuel was present throughout the engine fuel system, including the spray nozzle. A test run showed that the engine was capable of producing sufficient power.