Event Description
A helicopter departed from a fuel truck and, while climbing at approximately 10 feet above sloping terrain, experienced a partial loss of engine power. The aircraft settled and impacted the ground. The pilot reported that the engine was still spooling down as he exited the aircraft.
Engine Examination
Post-accident examination of the engine compressor section revealed that the internal plastic coating of the compressor case was cracked, with sections of the plastic missing. Erosion, which exceeded the manufacturer's allowable limits, was visible through the first four vane stages and was most evident in the lower case half.
Manufacturer and Maintenance Information
According to the engine manufacturer, unchecked compressor erosion can eventually result in a fatigue fracture of one of the vanes due to a loss of stiffness. The maintenance manual states that the compressor case should be replaced if any vanes are cracked, broken, or show evidence of tip rub on the rotor spacer. It further notes that corrosion or erosion can cause damage to compressor blades and vanes, potentially leading to engine failure. The manufacturer specifies that inspection intervals for the compressor case should be determined by the operating environment, but in any case should not exceed 300 hours.
Component History
The compressor case halves had been replaced in December 1996 and had accumulated approximately 600 hours at the time of the accident. They had not been inspected since being overhauled. The pilot reported that the helicopter had been operating in desert terrain.