The design cooling characteristics of the Engine Alliance GP7200 high pressure turbine (HPT) stage-2 nozzle components led to higher than expected metal surface temperatures during operation, rendering the nozzles susceptible to distress, premature degradation and failure.
The ATSB is satisfied that the action taken by the Engine Alliance will identify HPT stage-2 nozzle distress before it progresses to a stage that would impact flight operations. The ATSB would like to continue contact with the engine manufacturer regarding any new information on the conditions leading to the event.
As of 20 November 2012, all engines in the operator’s fleet of A380 aircraft had the new nozzles installed as per SB EAGP7-72-127.
As of 20 November 2012, all engines in the operator’s fleet of A380 aircraft had the new nozzles installed as per SB EAGP7-72-127.
The new HPT stage-2 nozzles have been installed across the majority of the high-time engines within the worldwide fleet. Additionally, there are repetitive inspections in place for both the new and old nozzle configurations and condition monitoring improvements have been put in place. The ATSB is satisfied that the action taken will reduce the prevalence of HPT stage-2 nozzle distress and will identify nozzle distress before it progresses to a stage that would impact flight operations.
Prior to the occurrence, Engine Alliance had already made design changes to the HPT stage-2 nozzle design to improve durability. On 6 December 2012, the engine manufacturer released a service bulletin (SB EAGP7-27-190) which provided on-wing inspection instructions for susceptible HPT stage-2 nozzles. When similar nozzle distress was discovered on an engine with the new configuration nozzles installed, the engine manufacturer released another service bulletin (SB EAGP7-72-262) with similar inspections to those for the older nozzles. The engine manufacturer is continuing to study the cooling characteristics of the HPT stage-1 nozzles, stage-1 shrouds and the stage-2 nozzles for potential further design improvements.
The ATSB is satisfied that the action taken by Engine Alliance, in combination with others, adequately addresses the safety issue.
An airworthiness directive (AD) was released in January 2013, AD FAA-02-06, which required initial and repetitive borescope inspections and removal from service before further flight if one or more burn holes were detected in pre-SB EAGP7-72-127 HPT stage-2 nozzles.
The ATSB is satisfied that the action taken by the FAA in combination with others adequately addresses the safety issue.
