Pratt & Whitney has selected its own five-stage high pressure compressor (HPC) for the PW6000 engine for the Airbus A318 over a "back-up" six-stage design developed and tested by partner MTU of Germany.

"We made a recommendation, and we reviewed that with Airbus and the airlines, and we're all reading from the same page" says PW6000 programmes vice president, Tom Davenport. "It is the best approach to certification" says Davenport who adds the MTU alternative was passed over because "...we had more data on the five-stage design because we'd started the programme with it."

The decision hinged on the outcome of test results from P&W's rigs which incorporated several changes to improve the flow of the compressor and its overall efficiency. Shortfalls in both areas were discovered during tests late last year, prompting MTU to accelerate on-going development work on an alternative design called the HDV12. P&W meanwhile improved sealing to reduce stage-by-stage leakage between blades and vanes, and revised the contours of the flowpath to improve stage matching.

"Efficiency was significantly lower than we had built it for, and the compressor wasn't pumping enough air" says Davenport, adding that the latest results show the issues have been mostly dealt with by the redesign. "The MTU compressor could have been a solution had we not had our own, but the day comes when you have to make a decision." P&W believes that sticking with the five-stage HPC means it will be able to meet the original October 2001 certification target, as well as the first flight target on the Airbus A318 of January 2002.

A full-up engine with 75% of the improvements will be tested in an altitude chamber at the Arnold Engineering Development Center in late November, while a test planned for March 2001 will incorporate the remaining new features. All are expected to be flight tested in a third phase of tests on the company's Boeing 720B testbed in May.

Four flight tests have been conducted since the initial sortie on 21 August and P&W plans to accumulate between 50h and 75hduring the current test phase. A second test period is planned for January.

Source: Flight International