Investigation of failure in main fuel pump of an aeroengine

There was an accident to a fighter aircraft. Investigation revealed that the accident was caused due to loss of power in the engine as a result of failure in the main fuel pump (MFP). The MFP was multi-plunger type. On dis-assembly, the MFP was found severely damaged and there were fractures in one plunger and four springs. Through systematic metallurgical investigation and analysis, the sequence of events leading to the failure in the MFP was established. The primary failure in the MFP was the fatigue fracture of springs. The fatigue crack initiation could be attributed to pitting corrosion on the surface of the springs. Because of multiple fractures in one of the springs, there was impact load on the corresponding plunger, which resulted in generation of an overload crack. This crack had further propagated progressively by fatigue mechanism culminating in fracture and loss of material from the side wall of the plunger. Subsequently, there was fuel leakage internally in the MFP with the resultant reduction in the fuel delivery pressure. Due to insufficient fuel supply, there was winding down of the engine RPM leading to loss of thrust. After establishing the sequence of failure in the MFP, investigation was carried out to identify the cause for the corrosion on the surface of the springs. It was established that the raw material (wires) used for the manufacture of the springs had developed corrosion pits on the surface due to improper storage.