Accident Overview
On June 11, 2019, at about 2230 Alaska daylight time, a Helio H-391B airplane, registration N10CJ, was involved in an accident near Hope, Alaska. The private pilot and a pilot-rated passenger were uninjured. The airplane sustained substantial damage during the landing. The flight was conducted as a personal operation under Title 14 Code of Federal Regulations Part 91.
Sequence of Events
The pilot reported that while flying over a natural gas pipeline, the engine began to surge and run rough, accompanied by a decrease in manifold pressure. He cycled the throttle lever, set the mixture 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 (engaging carburetor heat) with no effect on engine performance.
Although the pilot was able to maintain altitude, engine power remained limited. He located an abandoned airstrip along the pipeline road and initiated an approach to the north. The pilot stated that during the approach, he reduced power too late, causing an overshoot of the best landing area, and the airplane drifted right during the landing. During the landing roll, the right wingtip struck vegetation, and the airplane ground looped, impacting trees. The accident resulted in substantial damage to the left aileron and both sides of the stabilator.
Previous Engine Issues
The pilot noted that the engine surged slightly during the takeoff before the accident but not enough to cause concern. Approximately two months before the accident, the airplane had experienced a surge and partial loss of power during takeoff. A mechanic inspected the engine and conducted compression tests at that time, with no abnormalities found.
Post-Accident Examination
After the accident, the engine remained attached to the airframe, with all fuel, oil, ignition, and air lines secure. A fuel sample from the gascolator showed no contamination and was consistent with aviation fuel. The fuel filter was clear of debris. Continuity of the engine and flight control systems was confirmed. The propeller blades were secure in the hub with no oil leaks. The engine started and accelerated smoothly, and the propeller control cycled three times with corresponding changes in manifold pressure, RPM, and oil pressure. The RPM was increased to a maximum of 3,400 for 5 seconds with no surges noted.
The propeller governor (Hartzell B-3) was removed and bench-tested at a Hartzell facility, revealing no anomalies.
Inspection Findings
No evidence of any preexisting engine, propeller, or airframe discrepancies that would have precluded normal operation was found.