October 23, 2012
Operators of Rolls-Royce Trent 900-powered Airbus A380s have been instructed to inspect, and if necessary replace, parts of seals around the low pressure turbine (LPT) following damage to an engine caused by vibration.
An airworthiness directive issued by the European Aviation Safety Agency (EASA) says that the condition, if not corrected, could lead to cracking developing in the engine’s LPT second stage, “possibly resulting in an uncontained engine failure and subsequent damage to the aircraft.” The issue, which is not related to the oil-system problems that led to the uncontained failure of a Trent 900 on a Qantas Airways A380 in Singapore in 2010, was uncovered when debris was found in the tailpipe of an engine that had experienced increased vibration during a revenue flight.
The inspection revealed the turbine disc had lost material from part of the interstage seal, sending parts into the downstream LPT stages. Preliminary findings indicate that fins on the interstage seal had “rubbed into the stage 2 honeycomb seal, which overheated and cracked, finally resulting in releasing a portion of the ISS (interstage seal) area of the disc.”
The AD, which is effective as of Nov. 5, says inspections must be conducted within 10 flights if an engine health monitoring system picks up vibration levels that exceed the preset alert limits.
In August, EASA issued an AD calling for inspections and replacement if needed of the Trent 900 LPT shaft and bearing housing end cover. The action followed an in-flight turn back which resulted from the seizing up of the low pressure system in one of the A380’s engines. The fault was traced to oil starvation of the bearings caused by a fracture in an oil transfer tube. It had fractured because a support piece was missing.