Fatigue-Induced Crack an Aircraft Fire Extinguisher Outlet Discharge System: A Maintenance Case Study of an Airbus A330-900

This study analyzes a crack detected on the outlet discharge component of an Airbus A330-900 engine fire extinguisher system during C-Check maintenance. Because this component forms part of the extinguishing-agent distribution path to the engine nacelle, cracking may cause leakage, reduce discharge pressure, and compromise fire-suppression effectiveness. A real maintenance case study approach was applied, integrating inspection records, visual observations, operational context, fatigue interpretation, Paris Law-based crack-growth simulation, safety factor evaluation, and Failure Mode and Effects Analysis. The crack length was less than 5 mm and was detected after approximately 5,642 flight cycles. A representative stress amplitude of 95 MPa was used in the crack-growth simulation. Using representative Paris Law parameters, the MATLAB simulation predicted crack growth from 1.00 mm to approximately 5.00 mm after about 5,500 cycles, which was comparable with the verified aircraft exposure of 5,642 flight cycles and 10,834 flight hours. The safety factor was 1.2, while the FMEA produced a Risk Priority Number of 270. Post-replacement operational testing confirmed restored serviceability, with no observable leakage and normal flow characteristics. The findings support fatigue-induced crack propagation as the most plausible mechanism, accelerated by vibration-induced stress and thermal cycling.