firstfloor
This is from Flightglobal/Insight:
Qantas disclosed in an affidavit on 2 December that there are three modification standards - designated A, B and C - for the HP/IP support structure on the Trent 900 series. The document specified the failed engine as an 'A' modification powerplant.
According to Rolls-Royce's engine manual, the life of the 'A' support structure was limited to 2,000 cycles, said the airline. The 'B' modification was issued in December 2007 and its life limit extended to 14,800 cycles. The latest 'C' modification standard was introduced in April 2009 and has unlimited life, says Qantas.
The Australian Transport Safety Bureau declared its investigation was concentrating on 'A' and 'B' standard engines.
Powerplants with the 'C' modification status are not affected, because they do not have the same oil feed stub pipe installation, which is considered central to the engine failure chain.
Investigators believe that the stub pipe developed a fracture in a section with a small wall thickness, which led to an oil leak and fire in the HP/IP structure cavity. This thin wall section has been confirmed as a result of the manufacturing process.
EASA issued the revision of the second emergency directive this week, stating: "Manufacturing and inspection data, and stress analysis performed by Rolls-Royce, now confirm that oil feed tubes with a defined minimum thin wall section feature a higher life and lower risk of fracture." This would allow longer service periods for respective engines before the inspections.
The "A" Mod Qantas #2 engine (677 cycles total) didn't quite make it to the 2000 cycle limitation.
Turbine D