Citing four foreign accidents in two years involving uncontained engine failures, the NTSB Thursday issued recommendations that ask the FAA to require GE to redesign a specific engine component. The failures (one each on two Boeing 747s, an Airbus A300 and a DC-10) did not result any injuries or death, but the NTSB believes they presented direct hazards to the aircraft, the passengers and aircraft systems. An uncontained engine event results in fragments of rotating engine parts penetrating and exiting through the engine case. The NTSB would like to see the FAA require operators of CF6-45/50 engines to perform recurrent borescope inspections and recurrent fluorescent penetrant inspections, until GE provides a redesigned substitute low-pressure turbine stage 3 disk and operators have it installed. The NTSB believes the disks can “fail unexpectedly when excited by high pressure rotor unbalance.” The board’s recommended timeframe for replacement is “at the next maintenance opportunity.”
According to the NTSB, engine cases are not designed to contain failed turbine disks. “Instead, the risk of uncontained disk failure is mitigated by designating disks as safety-critical parts, defined as the parts of an engine whose failure is likely to present a direct hazard to the aircraft. The four failures noted by the NTSB occurred on aircraft flown by Saudi Arabian Airlines, Arrow Cargo, Jett8 Cargo and ACT Cargo. The timeframe for the incidents extends from July 4, 2008, to April 10, 2010. The full test of the NTSB’s safety recommendation letter to the FAA is available here: (PDF).
