ANC19LA027

On June 11, 2019, about 2230 Alaska daylight time, a Helio H-391B airplane, N10CJ, sustained substantial damage when it was involved in an accident near Hope, Alaska. The private pilot and pilot-rated passenger were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that, while flying over a natural gas pipeline, the engine started to surge and run rough, and the engine manifold pressure decreased. He cycled the throttle lever, increased the mixture lever to full rich, and turned on the electric fuel boost pump, but full power was not restored. The pilot-rated passenger pulled the carburetor heat lever out (carburetor heat on) with no effect on engine performance. The pilot was able to maintain altitude, but engine power was limited, so he searched for a precautionary landing site. He located an abandoned airstrip along the pipeline road and performed an approach to the north. The pilot reported that during the approach, he reduced power too late, which resulted in an overshoot of the best landing area, and that the airplane drifted right during the landing. During the landing roll, the right wingtip impacted vegetation, and the airplane ground looped and impacted trees, resulting in substantial damage to the left aileron and both sides of the stabilator. The pilot stated that the engine surged slightly during the takeoff before the accident, but not enough to concern him. About two months before the accident, the airplane experienced a surge and partial loss of power during takeoff. A mechanic inspected the engine and conducted compression tests with no anomalies noted. After the accident, the engine was intact and attached to the airframe with all fuel, oil, ignition and air lines secure. A fuel sample drained from the gascolator contained no contamination and was consistent with aviation fuel. The fuel filter was clear of debris. Continuity of the engine and the flight control system was established. The propeller blades were secure in the hub with no oil leaks observed. The engine started and accelerated smoothly and the propeller control cycled three times with corresponding change in manifold pressure, rpm, and oil pressure. The rpm was advanced to a maximum of 3,400 rpm for 5 seconds with no surges noted. The propeller governor (Hartzell B-3) was removed and bench-tested at a Hartzell facility with no anomalies noted. There was no evidence of any preexisting engine, propeller, or airframe discrepancies that would have precluded normal operation.