Discovery of Foreign Object
Damage to the high-pressure compressor (HPC) section and the discovery of a screwdriver tip in the cooling cavity adjacent to the combustion chamber were consistent with the tip falling into the low-pressure compressor (LPC) bleed duct and passing through the interstage duct into the HPC.
Damage Analysis
The lack of damage to the LPC indicated that the screwdriver tip was not foreign object debris (FOD) from the runway. Damage to a rear fairing screw suggested that the tip was likely left in the screw or fell into the bleed duct during maintenance.
Failure Sequence
At the next engine start-up, the tip traveled through the HPC, striking various components and leaving witness marks, before being held captive adjacent to the combustion chamber. Evidence showed that fatigue cracks initiated from the impact damage in a stage 5 compressor blade and a stage 6 vane. These cracks propagated under aerodynamic forces, vibrations, and, for the blade, centripetal forces, until one reached a critical size.
Engine Surge Event
The engine surge occurred during application of take-off power and acceleration of engine internals. It is more likely that the blade failed first due to increased centripetal acceleration, but regardless of whether the blade or vane failed first, one likely impacted the other. Both then caused downstream damage, including the failure of five additional compressor blades. The resulting disruption to aerodynamic flow through the HPC allowed the engine to surge and led to loss of engine performance.