Despite some early issues, Rolls-Royce appears extremely pleased with the first couple of years of service experience with the Trent 500 on the Airbus A340-500/600.

"There has been a big ramp-up in terms of engines in service, but as far as overall reliability is concerned the statistics are the best we've ever had for a Trent engine," says R-R head of marketing Airbus programmes Alistair Coast-Smith. "As it is operating on the longer-range routes, we are rapidly building hours, and the removal rate and in-flight shutdown [IFSD] rates are both better than we had on either the Trent 700 or 800 at this stage," he says. Based on a 12-month rolling average, the unscheduled removal rate is 0.069/1,000h, while the IFSD is at 0.004/1,000h.

The Trent 500 has the same 2.47m (8ft) -diameter fan as the Trent 700, married to a scaled version of the Trent 800 core. The engine undertook 47h of flight testing during 29 sorties on board Airbus's A340-300 testbed, beginning in June 2000. UK certification was achieved slightly ahead of schedule in December 2000.

As of late April 2005, 232 engines were in daily service on the growing fleet of 58 aircraft, with 1.2 million engine hours accumulated on more than 155,000 cycles. "We have already reached quite a mature level of experience," says Coast-Smith, who expects the trend to continue with between 100 and 150 new engines a year due for delivery over the 2006-7 timeframe.

The early-service experience was marked by three main issues, all of which R-R says are now behind it. The earliest of these was an oil seal problem that was identified during the latter stages of the development programme before entry into service in August 2002. "We already had a planned programme to replace the oil seal [in the low-pressure/intermediate-pressure internal gearbox] when it entered service," says Coast-Smith, who adds the issue caused excessive heating of the oil, which led to early degradation.

All new production engines are fitted with the improved seal, while only three in-service aircraft now require modification.

A second issue concerned tip rubbing on the fifth and sixth rotors of the eight-stage intermediate pressure compressor (IPC), and has caused at least three unscheduled removals from aircraft operated by Lufthansa. R-R began an urgent modification effort that initially involved slight cutbacks to the IPC blades. "But we still had some evidence of rubbing, so we made further cutbacks," Coast-Smith says.

Engines were removed for IPC module replacement on an "at-risk" basis, the actual risk factor being calculated as a function of accumulated cycles and remaining "bedding-in time".

As IPC cutback inevitably degraded efficiency, a longer-term solution was concurrently developed with "an aggressive 3D [three-dimensional aerodynamic design] approach," says Coast-Smith.

The result is the introduction of more advanced Trent 900-style 3D blades, which are "available now, and coming into the fleet over the next year or so", he says.

The third issue concerned a problem with the Goodrich-supplied electronic engine control (EEC), which was "easily identified", says Coast-Smith. The issue was related to the failure of a specific capacitor on the EEC board that triggered at least one IFSD incident. A fleet-wide retrofit was completed by October 2004, he says. For the longer term, R-R has developed a second bill of materials improvement to the Trent 500, dubbed the "A2" standard.

The upgrade was introduced late last year and includes end-of-wall profiling in the five-stage low-pressure turbine section, plus weight-saving hollow wall improvements. Other changes include the use of advanced shaped metal deposition technique in place of standard forging processes to make fan outlet guide vanes and "a few other tweaks", says Coast-Smith, who adds that the overall improvements produce a net 1% fuel burn saving.

Overall, R-R remains confident the relatively low operating thrust levels of the engine, which is certificated at 60,000lb thrust (267kN), but used at derated levels of 53,000-56,000lb, will help produce record setting time-on-wing and performance retention levels as the years go by. The engine is demonstrating "excellent temperature margin retention", Coast-Smith says.


Source: Flight International