Rolls-Royce increased the rotor tip clearances between the engine casing and intermediate pressure compressor (IPC) blades across various stages of newly manufactured Trent 700 powerplants, following an in-flight power loss on a Singapore Airlines Airbus A330-300 on 23 May 2015.
The modification was revealed in a final report by Singapore's Transport Safety Investigation Bureau on the incident.
The aircraft, bearing registration 9V-SSF, was operating enroute to Shanghai from Singapore when the incident occurred at 12:56 local time, as it encountered an area of adverse weather.
The TSIB found the flight crew received a message on the aircraft’s Electronic Centralized Aircraft Monitoring system (ECAM) display indicating that the aircraft’s right engine had surged. Before they took action, the right engine self-recovered from the surge, but the ECAM message was replaced by another message indicating that the left engine had surged.
The flight crew declared a mayday and shut down the left hand engine, before descending to a cruise level of 26,000ft. After discussing diversion options, the crew decided that it would be better to continue to Shanghai to avoid going through more weather cells.
They subsequently were able to restart the left engine and continued to its destination with both engines running normally, and cancelled the mayday. There were no injuries to the 192 passengers and crew on-board.
Analysis of the aircraft's flight data recorder showed that over 12 seconds the right engine surged three times and the left twice. No damage or faults were found, however, when inspections were carried out on the engines at Shanghai, and the aircraft was cleared to return to Singapore.
Upon its return, the left engine was removed and disassembled, which revealed signs of heavy rubbing of the rotor path abradable lining at Stages 3 and 6 of the IPC. Some IPC blades also had grey dust deposits of aluminium and silicon, which were consistent with the materials in the lining.
A thermal analysis by R-R found that during weather conditions experienced in the flight, the engine casing may have contracted as a result of water droplets or ice crystals being centrigued out of the IPC, bringing the lining into contact with the IPC blades and causing some of the material to separate.
The TSIB believes that those separated pieces of lining entered the combustion section and ignited, causing a temporary disruption of airflow through the engine and the rapid surges.
R-R subsequently increased the clearance between the IPC blades and the engine casing. SIA also implemented a policy of not pairing new engines together on its A330 fleet, to avoid the likelihood of twp new engines encountering the same issue.
In association with Airbus, R-R will also apply a modification to the electronic engine control logic on all newly manufactured Trent 700s to reduce the display time for the engine surge ECAM checklist to less than 10 seconds.