Accident Overview
On October 27, 2020, at about 1133 Hawaii standard time, a Hughes 369D helicopter, registration N58251, was substantially damaged when it was involved in an accident near Honolulu, Hawaii. The pilot was not injured. The helicopter was operating as a Title 14 Code of Federal Regulations Part 133 external load flight.
Sequence of Events
The pilot reported that as he began to lift the external load off the ground, he heard the main rotor rpm start to decrease. The ENGINE OUT horn activated, and the ENGINE OUT light illuminated. Realizing something was wrong, he jettisoned the external load. The main rotor rpm continued to decrease. He maneuvered the nose of the helicopter downhill to gain airspeed and lowered the collective. The main rotor rpm did not recover, so he increased collective to cushion the impact with trees. The main rotor blades impacted the trees, and the helicopter came to rest upright in heavy vegetation on a ridge. After the impact, the engine was still operating, and the pilot pulled the fuel shut-off lever and closed the throttle to shut down the engine.
Damage
The helicopter sustained substantial damage to the main rotor blades, the fuselage, and the tail boom.
Post-Accident Examination
Examination of the helicopter after recovery revealed anomalies in the start fuel pump. The fuel system was a suction-type system with two interconnected fuel cells. The start pump was a submersible, single stage, centrifugal, constant displacement type mounted in the left fuel cell. A small piece of fibrous debris was observed on one of the slots in the bypass inlet cover. No debris was found on the screen filter over the pump inlet. During removal of the bypass inlet cover and pump inlet screen filter, the circlip (retaining ring) and pin that held the flapper valve in place in the bypass inlet were missing. The flapper valve was wedged against the sidewall of the bypass inlet, obstructing about 50% of the discharge port. The pin was later located in the fuel line between the start pump and the engine-driven fuel pump, lodged on an elbow where the fuel line went through the firewall. The circlip was not found. No other anomalies with the start pump or other mechanical malfunctions were found that would have precluded normal operation.
Maintenance History
The start fuel pump manufacturer reported that the unit was originally manufactured in December 2014. It was received at an FAA-certified Part 145 repair station in April 2019 for overhaul. The overhauled start fuel pump was reinstalled by the operator on October 4, 2019, and the helicopter was returned to service.
Prior Event
About 30.5 flight hours before the accident, the engine lost power during a test flight, resulting in an off-airport autorotation. After the engine failure, the company performed a series of checks on the helicopter and engine runs, and the helicopter was returned to service on October 20, 2020. The company reported that after this event, they operated the helicopter during normal operation with the start fuel pump ON.
Maintenance Inspection
The operator’s director of maintenance reported that no maintenance was performed to the start fuel pump. Inspection included ensuring that the screen was not clogged and turning the pump on to listen for proper function. Their inspections revealed no anomalies before the accident.