Accident Overview
On July 6, 2022, at about 1015 central daylight time, a Hiller UH-12E helicopter, registration N64272, sustained substantial damage in an accident near Becker, Minnesota. The helicopter was operating under 14 Code of Federal Regulations Part 137 as an aerial application flight. The pilot, who was the sole occupant, was seriously injured.
According to information collected by a Federal Aviation Administration (FAA) inspector, the pilot was applying product to a potato field when he felt a small jolt, and the helicopter subsequently collided with terrain.
Post-Accident Actions
The operator transported the helicopter back to their facility approximately one week before notifying the National Transportation Safety Board (NTSB) or the FAA of the accident. As a result, neither agency was able to perform on-scene documentation. The operator reported that the main rotor mast had failed. The yellow blade was found about 500 ft west of the main wreckage, and the blue blade was found about 300 ft east of the main wreckage. The mast, along with a part of the transmission, was located about 150 ft northeast of the blue blade.
Attempts to retrieve the parts from the operator were unsuccessful. When the NTSB reestablished contact with the owner, he had already disposed of the parts.
Maintenance History
An FAA review of maintenance records revealed that the main rotor hub (part number 51437-23) was installed on the helicopter on December 14, 2018. Four days before the accident, a mechanic performed a 100-hour inspection, which included compliance with Airworthiness Directive (AD) 73-20-03. This AD requires dye penetrant inspection of the main rotor hub at 50-hour intervals to detect cracks. The helicopter had accumulated 9 flight hours since the inspection.
Rotor Hub Examination
The NTSB Materials Laboratory reviewed photographs of the broken rotor hub. The photos showed evidence of several preexisting, progressive fatigue failures.