Trent 900 IP turbine in the spotlight as QF32 investigation unfolds

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The Trent 900s on Qantas’s A380s, which are officially known as the Rolls-Royce RB211 Trent 972-84, feature a 72,000lb thrust rating, the higher of two available. Lufthansa and Singapore Airlines selected the 70,000lb rating. The Trent 900 is rated at 76,000 and 80,000lbs of thrust, but both are reserved for the larger A380-900 and A380-800F if/when they begin development.

While the six Qantas A380s remain grounded at this hour, the Australian’s Steve Creedy reports that the investigation has focused on Qantas’s selection of the 72,000lb thrust rating, for its longest routes.

Engineers believe the higher thrust levels at which the carrier operates its Rolls-Royce Trent 900 engines may result in resonating vibrations that cause oil lines to crack.

The theory has emerged after in-depth inspections uncovered oil in three A380 engines in areas where it should not be present.
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The Qantas A380 involved, which came into service two years ago, was also used for the trans-Pacific story. The oil leaks in the three engines, found in the intermediate pressure turbine area housing a disc similar to the one that disintegrated in last week’s spectacular mid-air drama, caused spotting and pooling that had the potential to spark damaging fires in the engine.

The hunt is on for the second part of the missing turbine gear, believed to be somewhere on Batam Island in Indonesia. The first part of the geared disk was recovered shortly after the incident last week. David Epstein, Qantas general manager , says of the number two engine: “There doesn’t appear to be a disk there at the moment. Virtually that entire area, the intermediate chamber of the engine, has disappeared.”

Already grappling with intermediate-pressure turbine and oil build up issues on its Trent 1000, which powers the Boeing 787, Rolls-Royce announced Monday it had definitively determined that the uncontained failures on the 900 and the 1000 were “unconnected”. 

The intermediate-pressure turbine, which is part of Rolls-Royce three-shaft engine architecture, is unique among the large commercial transport engines. Competitors Pratt & Whitney and General Electric have a two-shaft architecture. The three-shaft architecture allows each part of the engine’s core to spin at an optimized speed. The three shafts, which run concentrically, host the low, intermediate and high pressure elements.

The intermediate pressure (IP) compressor and turbine, which are hosted on the same shaft, are allowed to rotate faster than the fan, requiring fewer stages. The result is a shorter and lighter engine.

The Trent 900 architecture features a 116in front fan, which acts as the engine’s single-stage low pressure (LP) compressor, followed by an eight-stage IP compressor, six-stage high-pressure (HP) compressor, single annular tiled combustor with 20 fuel injectors, single-state high pressure turbine (drives the HP compressor), single-stage IP turbine (drives the IP compressor) and a five stage LP turbine (drives the front fan).

During its 90th birthday celebration this past weekend, Qantas displayed one of its grounded A380s along with past and present members of the carrier’s fleet. Along with an A330 and 747-400, Airbus cracked open the cowl of the Trent 900 on the A380 providing visitors an up-close view of the engine that was busy making less-positive headlines around the globe.

During this same period, Rolls-Royce issued a Trent 900 service bulletin, NMSB72-G589, whose contents is currently unknown, but it is believed to establish the inspection guidelines for the Qantas, Singapore and Lufthansa fleets. No one outside Airbus, Rolls-Royce, regulatory authorities and operators have seen this document.

While Singapore and Lufthansa A380 fleets operate unincumbered right now, Qantas believes its fleet could return to service in no less than 72-hours (Thursday evening local time), undoubtedly under the close watch of Airbus, Qantas, Rolls-Royce and the traveling public.