US engine maker Pratt & Whitney expects to decide on 15 May whether to offer its PW4098, at a 445kN (100,000lb)-thrust rating, for the proposed ultra-long-range Boeing 777-200X and extended-range -300X.

The future direction of the PW4000 series growth, and possibly the loyalty of some major Asian P&W-powered-777 customers, rests on the decision. P&W otherwise faces the expensive option of a new growth-derivative engine or losing potential market share. If the decision is positive, it would bring the engine maker back into head-to-head competition with General Electric and Rolls-Royce, now offering higher-thrust powerplants. "I'm 80% confident that we have a 100,000lb engine," says P&W senior vice-president for propulsion systems, Bob Leduc, who adds that the verdict will also be influenced by where Boeing "-stabilises the weight of the 777".

P&W is the last to show its hand in the engine makers' competition to study 445kN powerplants for the new heavyweight 777 variants. Until now, P&W has maintained that the 436kN PW4098, in development for the 777-300, was the highest-powered engine to which it was willing to commit. This was largely because of the high costs already experienced in the 777 engine-development programme, uncertainty over the size of the projected -200X/300X market, significant competitive discounting and low returns.

The company's decision to consider using the PW4098 for its 445kN offering is based on better-than-expected results from the engine-test effort. "The results are so encouraging that there is a possibility of doing a 100,000lb-thrust engine without major changes," says Leduc. The tests have shown "-component efficiency which exceeded expectations and higher-than-expected flow-capacity results in the low-pressure compressor", he says.

Most efficiency gains are attributed to improved "Super Nastar" high-pressure compressor blades used for the first time on a compressor design with the PW4090.

The move to a higher thrust setting, if sanctioned, will be watched by airlines such as Asiana and Korean Air, which are among leading candidates for the new 777 variants. Engineering sources within the airlines have voiced concern over P&W's method of growing thrust for the PW4098 by increasing the low-pressure rotor speed from 3,025rpm to 3,045RPM, and the effect which this may have on engine life and long-term performance. "This speed is higher than we envisioned three years ago," admits Leduc, who believes that concern is unwarranted.

Source: Flight International