DCA04IA002

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.

History of flight

On October 5, 2003, about 0155 eastern daylight time, an Edelweiss Airbus 330-243, HB-IQZ, experienced an engine fire and an uncontained engine failure of the No. 1 engine while climbing through flight level (FL) 230. The flight crew contacted Miami Center and requested clearance to return to Miami International Airport (MIA) Miami, Florida. The flight had departed MIA about 0145 on a regularly scheduled flight to Zurich, Switzerland, and was operating on an instrument flight rules flight plan under the provisions of 14 Code of Federal Regulations (CFR) Part 129. No injuries were reported for the 12 crewmembers and 171 passengers on board. Visual meteorological conditions prevailed at the time of the incident.

During interviews after the incident, the flight crewmembers reported that as they were climbing through FL 230, the master warning system annunciated along with a corresponding electronic centralized aircraft monitoring (ECAM) system message indicating turbine exhaust gas temperature overheat in the No. 1 engine. They reported that, shortly afterward, they felt heavy vibrations in the airplane and the No. 1 engine's fire warning system activated with a corresponding ECAM fire warning message. The pilots reported that they discharged one fire bottle into the nacelle but that the fire warning lights did not extinguish. They stated that a second fire bottle was discharged but that the fire warning lights remained illuminated. They indicated that an extra flight crewmember went back to the passenger cabin to see if he could inspect the engine from the passenger windows. The flight crewmember was unable to see any fire at that time but passengers reported that they had seen sparks, then white and orange flames.

The flight crew contacted Miami Center and requested clearance back to MIA. During the descent to MIA, at about 300 knots, the No. 1 engine fire warning lights extinguished. The pilot-flying requested a fire brigade to stand by for the landing, which the flight crew successfully performed with only the No. 2 engine operational. The fire brigade gave the go-ahead for the airplane to taxi up to gate E33. The flight crew had the airplane down safely on the ground within 20 minutes of the No. 1 engine failure. During the interviews held after the event, the pilot-flying stated that the air and ground traffic control communications were "great" and that the flight crew used crew resource management (CRM) effectively.

Engine information

Both engines were Rolls-Royce Trent 772-60/16 turbofan engines and were installed on the airplane when it was delivered new from Airbus on November 21, 2000; neither engine had been removed or overhauled since they were installed. Both engines had accumulated 15,169 hours time since new (TSN) and 2,348 cycles since new (CSN).

The Rolls-Royce Trent 700 engine is a three-shaft, high-bypass-ratio, modular turbofan engine with low pressure (LP), intermediate pressure (IP) and high pressure (HP) compressors driven respectively by LP, IP, and HP turbines through coaxial shafts. The LP system consists of a single-stage, wide-chord, hollow fan blade compressor driven by a four-stage turbine. The IP system consists of an eight-stage axial flow compressor driven by a single-stage turbine. The HP system consists of a six-stage axial flow compressor driven by a single-stage turbine. The combustion system is an annular construction incorporating fuel spray nozzles.

The initial on-scene examination of the No. 1 engine revealed that the IP turbine case exhibited a 360° circumferential rupture that created a gap between the IP and LP turbine cases. The IP turbine disk was still in place, but the disk rear drive arm was fractured circumferentially 360 degree around and all the blades were missing from the disk's blade slots. The HP/IP turbine bearing chamber external vent tube exhibited two burn-through holes located just outboard of the IP turbine case connection. The thrust reverser sustained damage to the inner and outer fixed structures. There was additional damage to the left wing and to the fuselage of the aircraft.

A borescope inspection of the No. 2 engine's HP/IP turbine bearing chamber external and internal vent tubes revealed the presence of black coke-like (black carbon deposits from the decomposition of oil under heat loads) buildup in the internal vent tube. The carbon obstruction largely filled the tube cross-section and was concentrated at the midpoint of the tube. The vent tube carries a mixture of air and oil droplets away from the bearing chamber.

Both engines were sent back to the Rolls-Royce facility in Derby, United Kingdom, for examination and teardown.

Teardowns and examinations

No. 1 Engine Teardown

Disassembly of the IP turbine nozzle guide vane support revealed that the only remaining part of the internal vent tube upper section was a small piece of the upper vent tube section with the IP turbine case connection fitting still attached, together with the outer heat shield . This small piece of the internal vent tube exhibited severe heat distress while the heat shield exhibited only minor pinholing damage. Apart from a short piece of the tube that remained attached to the HP/IP turbine bearing chamber, no portion of the internal vent tube lower section or its associated heat shield was recovered. The fracture surface of the vent tube lower piece appeared torn and exhibited moderate thermal damage.

Closer examination of the IP turbine disk drive arm fracture surfaces revealed heavy mechanical damage, smearing, and localized areas of a blue/black appearance. The drive arm was fractured in plane with the R850 cooling holes. The IP turbine disk was removed from the engine and was sent to the Rolls-Royce material laboratory for a detail metallurgical examination and dimensional inspection. Examination of the microstructure of the fracture surface through the R850 cooling holes in the disk drive arm revealed extensive oxidation and changes consistent with temperatures above 1000 degrees C (1832 degrees F). According to Rolls-Royce, the heat input into the drive arm was a combination of friction and fire.

No. 2 Engine Teardown

A borescope inspection of the entire HP/IP turbine bearing chamber and associated oil tubes revealed that the HP/IP turbine bearing chamber internal vent tube exit pocket¾part of the bearing chamber itself¾exhibited a considerable amount of soft granular carbon deposits at the outlet but that the pocket was not entirely blocked; however, extensive obstruction was noted approximately 2.25 inches outboard into the internal vent tube that prevented forward progress of the borescope.

An airflow check was performed on the blocked internal vent tube and revealed that air was able to pass through the carbon obstruction, indicating that the passage was not entirely blocked. Disassembly of the IP turbine nozzle guide vane support revealed that the HP/IP turbine bearing chamber buffer air tubes were crack free; however, large parts of the heat shield for both the lower internal vent and scavenge tubes were missing. In both cases, the tubes exhibited some fretting damage but neither of the tubes was breached. According to Rolls?Royce, tube frettage at this inboard location is not uncommon but, at the time of the event, there had been no reports of a breached tube.

Carbon Examination

Between February and May 2004, three-dimensional (3-D) neutron tomography was used to determine the extent and morphology of the carbon deposit in the No. 2 engine's internal vent tube. The tomography showed only partial blockage of the tube with carbon deposits. On completion of the tomography, the vent tube was cut open lengthways for visual inspection and analysis of the carbon deposit. The visual examination confirmed the 3-D neutron tomography findings. Rolls-Royce concluded that the morphology, locati