Boeing has revised its future 747 growth studies to include a 500-passenger stretch version with a larger wingspan, known as the -400Y Stretch, while dropping another long range variant dubbed the -400ERY.

The company stresses that the only new version of the 747 being formally offered to airlines is the 413,140kg -400IGW (increased gross weight) model announced in December 1997. The -400Y Stretch will build on many of the structural changes necessary for the -400IGW, but will be significantly larger, with a 9.4m fuselage extension. The key change to the -400Y is an extra 2.3m section to the inboard wing root area, increasing span to 69m. The larger wing root volume will house enough fuel to enable the aircraft to carry 500 passengers up to 13,875km (7,500nm). Maximum take-off weight would be more than 454,000kg. Although wing root inserts have been studied many times for the 747, the recent decision by Airbus to delay its rival A3XX has breathed new urgency into the project.

Boeing says that "-the study is more than just an exercise" and that it is aimed at capturing part of the projected A3XX market. No details of the proposed timescale have been released, although it is understood that airlines are being canvassed with a potential entry into service date of as early as 2003 - at least 12 months ahead of the A3XX.

"We are looking at new engines, but we're also considering derivatives in the 68,000lb [302kN] thrust area," says the company. The General Electric/Pratt & Whitney engine alliance has extended the thrust range of its GP7000 down to 302kN in response to Boeing's revised weight targets for the 747 growth options. The GP7000 is offered for the A3XX and 747 derivatives in competition with Rolls-Royce's proposed Trent 900.

Other 747-400 derivatives under study include the -400X stretch and the -400LRX. The basic stretch would entail a fuselage extension of 6.1m, providing room for an additional 75 passengers. This would take capacity to roughly 495 people, but with range penalties. This could be made up using belly tanks of the -400IGW.

The 375 seat -400LRX is "still in study", according to Boeing, and would combine the original -200 fuselage with the technology, structure and wings of the -400F freighter. The reduced weight of the upper deck would contribute to a range "in excess" of 14,800km.

Source: Flight International