Edelweiss Air Airbus Industrie A330 incident

Climbing through FL 230, an Edelweiss Airbus 330-243 experienced an uncontained engine failure of the No. 1 engine. The flight crew declared an emergency and returned to Miami International Airport, Miami, Florida, to execute an uneventful single-engine landing. Postincident examination revealed that an oil fire in the high pressure (HP)/intermediate pressure (IP) turbine bearing chamber internal oil vent tube of the No. 1 engine burned through the tube, allowing hot gases into the HP/IP turbine bearing chamber. The hot gases blew the oil past the oil seals, igniting the rear area of the bearing chamber and providing enough heat to fracture the IP turbine disk drive arm, which caused the disk to overspeed and release its blades through the IP turbine case. Some of the blades impacted the left wing and a portion of the fuselage. Due to the fire damage to the No. 1 engine and the loss of a significant portion of the internal vent tube and associated heat shield, the exact cause of the vent tube oil fire initiation is unknown. However, examination of the No. 2 engine's vent tube revealed that it was blocked with carbon deposits. Because both engines had the same operating time and history, it is likely that the event engine had a similar blockage of its vent tube and that the blockage contributed to the initiation of the oil fire.

At the time of the uncontained engine failure, Mobil Jet Oil (MJO) 291 was being used in the incident engines. MJO 291 was approved for use in Trent 700 engines in 1996 but Edelweiss was the only operator using that type of oil. The incident investigation revealed that the use of MJO 291 produced coking in the sister engine and, by inference, the incident engine's HP/IP bearing chamber internal oil vent tube which resulted in a catastrophic engine failure. There had been a demonstrated coking problem in the same area with another previously approved oil. A 1999 Rolls-Royce service bulletin (SB) removed ASTO 560 from the list of oils approved for use in Trent series 700 and 800 engines after it was found that significant carbon accumulation was confined to operations using ASTO 560. After the deletion of ASTO 560 from the list of approved oils, no significant buildup of carbon was found in engines over 10,000 hours. As a result, CAA and Rolls-Royce, based upon data available and mindful of the additional threat of a maintenance error associated with such inspections, deleted the 3,000-hour requirement for the on-wing inspection of the HP/IP bearing chamber internal oil vent tube for coking. If the 3,000-hour requirement to inspect for coking had remained in place, it is likely that the coking in the incident engines would have been found and the engine would not have suffered a failure. Each time a new oil is introduced, procedures should be developed and implemented to inspect those areas where engine testing or in-service experience has indicated carbon formation is possible - until such time as there is sufficient in-service engine data to support the case for no longer doing so.

The incident flight was on an ETOPS route, which, in the event of an engine shutdown, allows one engine operation for up to 180 minutes. It is recognized that if the flight crew did shut down one engine, the flight could have continued for that time with an unspecified risk for the remaining engine to fail. Since the sister engine had an unusual coke formation also, by both engines not being monitored after the induction of the new oil, it allowed for the potential of an erosion into the safety margin allowed by ETOPS. This investigation highlights that engine manufactures should take into account the level of risk associated with approving new engine/oil combinations. Operators also need to take into account the introduction of new oils into their fleets and ensure that sufficient evidence exists to support their use.

Verbatim NTSB analysis and probable cause from the NTSB dataset