Qantas details history of Rolls-Royce Trent 900 variants

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Qantas Airways has detailed the history of the Rolls-Royce Trent 900 powerplant variants that power its Airbus A380s in the affidavit and claim it filed against the engine manufacturer in Australia's Federal Court.

A Trent 900 engine experienced an uncontained engine failure on a Qantas A380 flight on 4 November. The A380 fleet's return to service after a three-week grounding has been dependent on the engine's three different modification standards.

After the 4 November incident, Qantas and Rolls-Royce agreed the carrier should not operate any engines with an "A mod" high-pressure (HP)/intermediate pressure (IP) support structure, the affidavit says.

Qantas can operate "B mod" and "C mod" engines, the affidavit adds. However, the engines are restricted to performing only 75 72,000lb full thrust take-offs. After that threshold has been reached, the engine requires replacement before being operated at any thrust level.

Prior to the incident, seven of 24 Trent 900s on Qantas' six A380 aircraft had the original "A mod" HP/IP support structure. According to Rolls-Royce's engine manual, the life of the "A mod" HP/IP support structure is 2,000 cycles, the affidavit says.

The Trent 900 engine that experienced the uncontained failure was an "A mod" powerplant, the affidavit says.

In December 2007 Rolls-Royce issued a modification standard, "B mod", for the HP/IP support structure. Prior to the incident Qantas had 16 of these engines. Their life was 14,800 cycles, the affidavit says.

Rolls-Royce issued the latest modification standard, "C mod", in April 2009, the affidavit says. Qantas operated at the time of the incident one such engine, which had an unlimited life cycle.

The affidavit and claim do not specify what changes were made between the modification standards.

Qantas' claim says Rolls-Royce is in breach of thrust specification and payload undertaking agreements.

Rolls-Royce wrote to Qantas during the tender process that the "thrust availability guarantee would provide cover against an engine's inability to achieve full take-off thrust whilst on a normal revenue flight, up to 2,000 cycles", the claim says.

Rolls-Royce also said a Trent 900-powered A380 could be "operated regularly and reliably on Qantas' existing international routes (including the LAX routes) with a profitable payload and without the engines having to be replaced at any point before the end of the projected useful engine life", the claim says.

Last week the Australian Transport Safety Bureau said it was focusing on "A mod" and "B mod" variants for having a faulty stub pipe that feeds oil to the HP/IP bearing structure. The "C mod" variant was not affected.

The ATSB identified a faulty stub pipe with a misalignment causing pipe thinning as the likely cause of the uncontained failure.

As a result of the finding, checks were ordered on 45 "A mod" and "B mod" Trent 900 engines, the ATSB has said. Inspections found three engines with a faulty stub pipe, including one on a Qantas A380 imminently due for arrival.