What happened
During a routine walk-around inspection, the flight crew identified a significant burn-through area on the outboard cowling of the number one engine. This visual anomaly prompted the immediate removal of the engine from service for a thorough disassembly and examination.
The investigation
Mechanics and investigators conducted a detailed teardown of the affected powerplant. The inspection revealed extensive thermal damage beyond the initial visual cue. Specifically, the fan duct and the outer liner of the engine combustion section were also found to be burned through.
Upon closer examination of the core components, the number 7, 8, and 9 combustion chambers were discovered to be partially burned away and severely distorted. Historical maintenance records indicated that these specific chambers had been previously removed and subjected to weld repairs approximately 16,000 hours prior to this failure event.
Findings
The investigation determined that the primary mechanism of failure was thermal fatigue. The repeated stress cycles associated with heating and cooling, likely exacerbated by the previous repair work, led to the structural degradation of the combustion chambers. This fatigue ultimately resulted in the burn-through of the chambers and the subsequent damage to the surrounding cowling and liner components.