Accident Details
On March 28, 2015, at approximately 1800 Pacific daylight time, a Hiller UH-12E helicopter, registration N130HA, sustained substantial damage after losing engine power and executing a forced landing about 6 miles east of Firebaugh, California. The aircraft was operated by Mid-Cal AG Aviation, Inc., under 14 Code of Federal Regulations Part 137 for agricultural aerial application. Day visual meteorological conditions prevailed, and no flight plan was filed. The local flight originated from a loading site approximately 6 miles east of Firebaugh around 1700.
Pilot Report
The pilot reported conducting a preflight check about 2 hours before takeoff, noting no anomalies. Prior to departing with the first load of insecticide, the fuel gauge indicated 24 gallons of fuel. Over 45 minutes, the pilot dispersed 10 loads. For the 11th load, he attempted a normal landing from a hover with 8 gallons remaining. During the landing flare, the engine momentarily sputtered. The pilot attributed this to fuel movement in the tank allowing air into the system. A graduated fuel stick then indicated 5 gallons remaining.
After adding 18 gallons of fuel and more insecticide, the engine ran for about 5–7 minutes at 2,500 rpm. The pilot visually scanned engine instrumentation before and during takeoff, observing no abnormalities. Following dispersal of the 11th load, the engine began to shake violently. The pilot turned left and oriented the helicopter into the wind, but the helicopter descended as engine power was lost. He performed an autorotation, and the helicopter impacted terrain, resulting in substantial damage to the tailboom.
Inspection Findings
The helicopter and engine were inspected on October 21, 2015, at the operator's facility. Examination revealed a separated throttle cable bracket mounted on the intake duct. Three rivets securing the bracket were sheared, and a fourth rivet was missing. A longitudinal snubber used as an engine mount was also sheared. Microscopic examination of the rivets (5–50X stereo-zoom) showed fracture surfaces consistent with overstress. The complete engine examination report is in the public docket. No evidence of pre-impact mechanical malfunctions that would have prevented normal operations was found.