The company must decide whether the Airbus A318 engine-part should be redesigned or replaced by an MTU design

Pratt & Whitney faces a one to two year delay in the delivery of production standard PW6000 engines for the Airbus A318, depending on whether it chooses to redesign its own high-pressure compressor (HPC) or replace it with a six-stage HPC being proposed by MTU, in order to fix a shortfall on guaranteed performance.

Airbus warns the delay opens up the prospect of it delivering the first CFM56-5BA8/9 powered production A318 aircraft ahead of the PW6000-equipped aircraft. The original schedule called for the delivery of the first PW6000-powered A318 to launch customer International Lease Finance (ILFC) in late 2002, followed by the initial CFM56-5 aircraft to Air France in September 2003.

P&W concedes that it faces "some technological challenges with the current engine" but says that it remains on schedule to certificate the engine in readiness for the start of A318 flight testing early in 2002. The company, however, will have to modify or change the HPC in the final production engine if it is to meet specific fuel consumption (SFC) guarantees made to airlines. It has declined to quantify the extent of the SFC shortfall, but outside sources have suggested it could be as high as 6%.

The root of the problem is P&W's five-stage HPC. Concerns over performance 15 months ago resulted in the company considering switching to MTU's proposed HDV12 design. P&W eventually opted to stick with its design, convinced it had resolved performance shortfall by improving gas path sealing and flow path contouring (Flight International, 19-26 September 2000).

Now P&W is once again looking at the German company's six-stage HPC and is understood to be running it on the PW6000 test rig to validate performance. MTU is already a partner on the PW6000 programme responsible for the low pressure turbine.

The alternative is that P&W redesign its own HPC by adding a sixth or perhaps even a seventh stage. The company believes that it could offset the increased weight from the additional stage by designing the first five stages around smaller and lighter blades and discs. Whichever route P&W elects to take, the net result will be to add at least 12 months to the time it takes to deliver an engine fully compliant with performance guarantees.

P&W is hoping that the fallout from such a delay will be cushioned by the fact that several customers, including ILFC and British Airways, are seeking to defer A318 deliveries in the face of the current economic situation. Of the five carriers that have ordered the aircraft to date, only Air France has so far selected the CFM56-5B powerplant. The A318 order backlog including leasing companies, totals 136 aircraft.

Source: Flight International