Incident Overview
As full power was applied for takeoff, the 6th stage disc on the intermediate compressor 6/7th rotor shaft assembly in the #3 engine ruptured. Pieces of the disc severed a fuel inlet line and penetrated the #1 engine and the fuselage. Fire warnings for both the #3 and #1 engines were activated, and engine fire bottles were discharged during the aborted takeoff. Residual fire in one engine was extinguished by airport firefighters.
Metallurgical Examination
Approximately 80% of the failed disc was recovered. Metallurgical examination revealed corrosion pitting and small fatigue cracks at the attachment holes. The largest crack measured 0.13 inches deep and 0.23 inches wide.
Overspeed Considerations
According to Rolls Royce calculations, the observed crack size would not have resulted in failure unless the N2 rotor RPM had reached 118%. A telltale marker for the flight engineer's #3 N2 gauge indicated 106% (red-line was 102.5%), but the marker was found to be out of calibration; therefore, overspeed was not verified. Maximum EPR for takeoff was within limits.
Service Bulletin Compliance
Service Bulletin (SB) RB.211-72-9569 required that rotors exceeding 14,000 cycles be removed by April 30, 1993. The failed rotor had accumulated 16,327 cycles. The SB was designated as 'S-mandatory' in the United Kingdom, but it was not mandatory in the United States.