Fuel contamination involving a Hughes Helicopters 369D, VH-MHE, Port Augusta Power Station, South Australia, on 11 April 1994

Circumstances

The helicopter had just lifted off and was about 30 feet above the ground when the pilot noticed that main rotor RPM was beginning to decay. He reduced collective pitch, but the helicopter lost height as the engine power slowly decreased towards flight idle.

Height could not be maintained with the power available, so the pilot had no option but to perform a downwind run-on landing onto rough terrain. The tail rotor struck the ground, and the tail boom was damaged by the main rotor blades. The engine was still running at reduced RPM when the helicopter came to rest.

Investigation revealed significant contamination in the airframe and engine fuel filters. The filters were not completely clogged, and the material was mainly of a sandy nature. Some of the material found in the filter bowls was probably displaced from the filter surface during the rough landing.

Engine components, including the fuel control unit, power turbine governor, fuel nozzle, PC air filter and all pipes and hoses were inspected by an approved overhaul facility.

Some of these components showed signs of wear sufficient to require overhaul before being returned to service but no fault could be found that would have definitely caused the power loss.

During the investigation it was found that the fuel supply hose became discoloured after being in contact with jet fuel for only a short period of time. Samples of the hose (both new and used) were sent for laboratory testing which revealed that the rubber compound used was not fuel proof, although it was rated for use with jet fuel.

Neither the partial filter clogging, the effects of wear in the engine fuel supply components nor the dissolved material from the faulty hose, individually, could explain the power loss. A combination of these factors at a time of high-power demand may have been sufficient to cause the loss of power.

Safety action

The Civil Aviation Safety Authority is aware of the information relating to the degradation of the interior of the fuel hose assembly and has taken it up with the hose manufacturer.