English: Four LPT stage 4 (S4) vane clusters weakened by an undetected sulfidation/corrosion attack disengaged at their inner attachment. The disengaged clusters displaced aft and contacted the S4 blades during operation. The contact machined a groove into the blade leading edges near the platforms. High cycle fatigue cracks initiating in the machined area of several blades propagated to overload separation. The blade liberation led to the separation of the remaining S4 blades and extensive downstream LPT blade and vane cluster damage. A large amount of metal debris was released into the gas path, loading the engine casings. The P-flange attachment hardware separated in overload, resulting in engine uncontainment.