Honolulu, HI, USA
N58251
HUGHES 369
During longline operations, the helicopter lost partial power and the main rotor rpm decreased. The pilot jettisoned the external load and the helicopter impacted trees, resulting in substantial damage. The engine continued to run after impact, and the pilot performed an emergency engine shutdown. Examination revealed that the start fuel pump was damaged. The circlip and pin that held the flapper valve in place in the bypass inlet were missing, and the flapper valve was wedged against the sidewall of the bypass inlet, obstructing about 50% of the discharge port. The pin was located in the fuel line between the start fuel pump and the engine-driven fuel pump; the circlip was not found. No other mechanical malfunctions were found that would have precluded normal operation. The pin found in the fuel line and obstruction from the flapper valve located in the start fuel pump likely induced restricted fuel flow from the engine-driven fuel pump to the engine, which resulted in a partial loss of engine power. Based on the available evidence, the reason for the separation of the circlip from the pin could not be determined.
On October 27, 2020, about 1133 Hawaii standard time, a Hughes 369D helicopter, N58251, was substantially damaged when it was involved in an accident near Honolulu, Hawaii. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 133 external load flight. 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. He then realized something was wrong and 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, and 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. The helicopter sustained substantial damage to the main rotor blades, the fuselage, and the tail boom. The helicopter was examined after recovery from the accident site. The fuel system was a suction-type system with two interconnected fuel cells located beneath the cargo/passenger compartment floor. The helicopter was equipped with a submersible, single stage, centrifugal, constant displacement type start pump that was mounted in the left fuel cell on the tank sump plate. When the start pump is on, the fuel is drawn in through the pump inlet by suction; when off, fuel is drawn in through a second parallel port, or bypass inlet, by the engine-driven fuel pump. The start fuel pump was removed for inspection, and a small piece of fibrous debris was observed on one of the slots in the bypass inlet cover. No debris was observed on the screen filter over the pump inlet. The bypass inlet cover and pump inlet screen filter were removed. During the removal, 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 and appeared to be obstructing about 50% of the discharge port. No other anomalies with the start pump were observed. The fuel system was examined to locate the circlip and pin. The pin was 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 evidence of any internal damage was observed in the start fuel pump and the fuel system. No other mechanical malfunctions were found that would have precluded normal operation. The manufacturer of the start fuel pump reported that the unit serial number was originally manufactured December of 2014. The unit was received in the FAA certified 14 CFR Part 145 repair station in April of 2019 for overhaul. The overhauled start fuel pump was reinstalled by the operator onto the helicopter on October 4, 2019, and the helicopter was returned to service. About 30.5 flight hours before the accident, the engine lost power during a test flight, which resulted 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 October 20, 2020. The company reported that, after this event, they operated the helicopter during normal operation with the start fuel pump ON. The operator’s director of maintenance reported that they performed no maintenance 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.
A partial loss of engine power due to an obstructed fuel line as a result of the separation of the circlip from the pin used on the fuel start pump. The reason for the circlip separation could not be determined based on the available evidence.
Source: NTSB Aviation Accident Database
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