What happened
The aircraft was cruising at flight level 310 when the number two engine suffered a catastrophic mechanical failure. The first-stage turbine disc separated from the assembly, resulting in an uncontained engine failure. High-energy debris from the disintegration penetrated the fuselage structure, causing rapid depressurization of the cabin.
Following the loss of pressure, the pilot initiated an emergency descent to a lower altitude. The aircraft continued under manual control and landed safely at Charleston, West Virginia, which was located approximately 50 miles from the point of failure. All passengers and crew evacuated without injury, though several oxygen masks failed to deploy automatically.
The investigation
Examination of the recovered engine components revealed severe rubbing and melting of the low-pressure turbine interstage seal. Additionally, the drive flanges connecting the first-stage (LP1) and second-stage (LP2) turbine discs were found to be separated.
The investigation identified a critical error in the maintenance procedure performed prior to the flight. Rolls-Royce repair scheme XRS 3505 outlines specific protocols for repairing these interstage seals. However, the repair facility utilized machining reference surfaces that differed from those specified in the official repair scheme. This deviation likely contributed to the improper assembly and subsequent failure of the seal under operational stress.
Findings
The root cause of the incident was traced to a maintenance error during the repair of the low-pressure turbine interstage seal. The use of incorrect machining reference surfaces led to a misassembled seal that could not withstand normal operating conditions. Rolls-Royce subsequently amended repair scheme XRS 3505 to make the procedure more tolerant to rubbing or misassembly of the low-pressure turbine seal, addressing the specific vulnerability exposed by this accident.