September 19, 2013
The Australian Transport Safety Board (ATSB) says new hardware, recurrent inspections and changes to engine monitoring “adequately address” its concerns about failures of high-pressure turbine nozzles in the Engine Alliance GP7200 turbofan engine for the Airbus A380.
Investigators determined that higher-than-expected metal surface temperatures had caused the failure of high-pressure turbine (HPT) second-stage nozzle guide vanes in a GP7270 turbofan on an Emirates Airline A380 in November 2012. The resulting damage caused the engine to shut down in flight.
The aircraft had departed Sydney Airport and was climbing through 9,000 ft. when the crew heard a “loud bang” and received an exhaust gas temperature over-limit warning for engine number three. The pilots dumped fuel and returned for a non-eventful landing.
Investigators later determined that the shutdown was the result of “significant internal damage” that began with the high-pressure turbine (HPT) second-stage nozzle failure, most likely caused by hotter-than-expected operating temperatures, according to a final report on the Emirates engine failure.
The issue is not related to the Qantas Airways A380 engine incident that occurred in 2010. In that case, a Rolls-Royce Trent 900 engine experienced an uncontained failure initiated by a cracked oil feed pipe in the high-pressure/intermediate pressure hub assembly. Debris from the engine caused multiple aircraft systems to fail.
In the Emirates incident, the ATSB says debris from the failure—consisting of nozzles, shrouds and shroud hangars—was ejected from the rear of the engine, with no threat to passengers or the aircraft’s structure.
During the aircraft’s previous flight, the engine health and trend monitoring system had identified shifts in number three engine parameters. An “urgent remote diagnostic notice” was sent to Emirates, notifying the carrier of potential deterioration of the aircraft’s number three engine high-pressure compressor efficiency. Emirates had scheduled an inspection when the aircraft returned to its home base in Dubai.
“At the time of the failure event, the engine’s exhaust gas temperature and high-pressure compressor trend monitoring criteria were not yet at a level that would have required an immediate inspection of the engine,” says the ATSB.
The ATSB notes that four other engines had experienced HPT second-stage nozzle “distress” in the four weeks preceding the Emirates incident, one of which already had received new nozzles that the Engine Alliance started offering in 2011, after discovering thermal distress in the components in a test engine.