Axial misalignment causes a fatigue failure -Quantas A380 incident

The ATSB which is conducting investigations into the engine failure incident that occurred to the Airbus A 380 aircraft on November 2010, has mentioned the following in a safety alert:"A subsequent examination of the aircraft indicated that the No 2 engine had sustained an uncontained failure of the Intermediate Pressure (IP) turbine disc. Sections of the liberated disc had penetrated the left wing and the left wing-to-fuselage fairing, resulting in structural and systems damage to the aircraft. The No 2 engine was removed from the aircraft and disassembled in an authorised engine workshop for examination, under the supervision of the Australian Transport Safety Bureau. In addition, a large section of liberated IP turbine disc was also recovered from Batam Island for examination. Those examinations are ongoing. Recent examination of components removed from the failed engine at the Rolls-Royce plc facility in Derby, United Kingdom, has identified the presence of fatigue cracking within a stub pipe that feeds oil into the High Pressure (HP) / Intermediate Pressure (IP) bearing structure. While the analysis of the engine failure is ongoing, it has been identified that the leakage of oil into the HP/IP bearing structure buffer space (and a subsequent oil fire within that area) was central to the engine failure and IP turbine disc liberation event.

Further examination of the cracked area has identified the axial misalignment of an area of counter‑boring within the inner diameter of the stub pipe; the misalignment having produced a localised thinning of the pipe wall on one side.

Misaligned stub pipe counter-boring is understood to be related to the manufacturing process. This condition could lead to an elevated risk of fatigue crack initiation and growth, oil leakage and potential catastrophic engine failure from a resulting oil fire".

Read the full report in this link. Those of you who are responsible for asset integrity in chemical plants - please note that it only requires a small error to cause a big disaster.