PRATT & WHITNEY is to launch a 436kN (98,000lb)-thrust derivative of its PW4000-series engine to power heavier versions of the Boeing 777, as well as the planned stretch model.

The two companies have formed a team to " information and work with airlines in order to determine thrust requirements and entry-into-service-date requirements for heavier gross-weight 777 models", says P&W.

The new engine, called the PW4098, will have a modified version of the current 2.9m-diameter fan and an upgraded PW4090 core. The 4090 was detailed exclusively in Flight International (27 July-2 August 1994).

Boeing remains coy about growth plans for the 777, but confirms that the heaviest estimated gross weight target of 287,150kg, " being re-looked at".

Comments by P&W president Karl Krapek suggest that the new target weight may be almost 3000,000kg. "The PW4098 will allow Pratt to easily power future versions of the 777 up to 660,000lb [299,640kg] in gross take-off weight," he says.

By having the more powerful engine available as an option, Boeing is likely to offer a longer-range version of the stretch and the B-plus 777 airframe from which it is derived. This could push the "B-plus" range from its current 13,650km (7,400nm), with 305 passengers in three classes, to around 14,250km, or well into the "C-market" category. Similarly, the extra power could allow the stretch to carry 450 passengers across a 10,200km range. The stretch 777 will be over 3m longer than the 747-400, at almost 75m.

P&W will achieve the extra 35kN of take-off thrust by modifying the aerodynamics of the current fan, but not increasing its diameter. It will also add a single stage to the PW4090's six-stage low-pressure (LP) compressor. Further aerodynamic improvements to the high-pressure (HP) compressor are also likely. Additional use of new materials and extra cooling in the HP and LP turbine may be needed, says P&W.

The PW4098 will be certified in September 1997, around 14 months after certification of the PW4090.

Commenting before the formal announcement on 17 February, Krapek said that no airline had yet selected a 435kN engine, but that Egyptair was lead candidate to launch the 777 stretch.

Egyptair issued a letter of intent for three 777s, plus two options, in October 1992.

Source: Flight International