History of Flight
On February 2, 2010, at approximately 1320 Pacific standard time, a Hiller UH-12E helicopter, registration N36MV, experienced a hard landing near Los Banos, California. The aircraft was operated by S and S Helicopters under Title 14 Code of Federal Regulations Part 137 for an aerial application flight. The certificated commercial pilot was not injured, but the helicopter sustained substantial damage. The local flight had departed from a field near Los Banos. Visual meteorological conditions prevailed, and no flight plan had been filed.
The pilot reported that he had just completed an aerial application over a wheat field and was returning to land. As he approached the landing area at an altitude of about 30 feet above ground level, he began to apply power, but the engine did not respond. He continued to twist the throttle, but it felt loose with no resistance, and engine speed did not change. He aborted the landing approach and turned the helicopter towards a larger open field. He circled the field about three times while attempting to diagnose the problem. He then elected to perform a run-on landing; during the landing approach, engine speed began to decrease, and the helicopter landed hard.
Damage and Examination
During the landing sequence, the tailboom separated from the aft bulkhead, and the lower fuselage sustained crush damage.
Post-accident examination revealed that the throttle control fitting, located at the aft end of the collective stick assembly, had become separated from the cam lever rod bearing. According to the Hiller service manual applicable to this helicopter, the throttle control fitting is connected to the cam lever rod with an AN23-16A bolt, NAS43DD3-4 spacer, AN960PD10L washer, and a NAS679A3 nut. None of these fittings were located on the engine deck, and examination of the control arm mating surfaces revealed no gouges or fretting signatures.
Maintenance History
According to maintenance logbook entries, the helicopter underwent an annual inspection on February 25, 2009, at an airframe total time of 6,815 flight hours. According to the FAA inspector who responded to the accident, the helicopter’s total flight time at the time of the accident was 7,064 hours.