Boeing’s third-generation 777 maps closely to 737′s evolution

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This week’s Flight International cover story offers the most comprehensive look yet at Boeing’s 777X concept, the third generation 777 with its new carbon fiber wing and emerging engine battle between incumbent General Electric, Rolls-Royce and Pratt & Whitney. 
If its conceptual performance goals are achieved, Boeing believes that the 777-9X could become the most efficient commercial aircraft it has ever built, touting a 21% improvement in per seat fuel burn and a 16% improvement in per seat cash operating costs, say those directly familiar with the plans to make the potential superlative a reality.
To look into Boeing’s history as it moved from the early 737-200 to larger -300 model, the first model of the Classic family, the incremental development of the narrowbody maps closely to the airframer’s continuous improvement strategy on the 777. 
The re-engining and wing lengthening of the 737-300 with the CFM56-3 engine, which was then in competition with the Rolls-Royce RJ500, provided the source of the improved efficiency and performance just as the transition from the 777-200ER and -300 to the -300ER and -200LR and its GE90-115B.
When it developed the 737-300, 18 of the 21% fuel burn improvement on the 737-300 came directly from the higher bypass CFM56-3 engine, according to the Flight International archives from February 1982. 
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During the development of the Next Generation 737 a decade later, Boeing would offer an updated CFM56-7B engine along with a 16% larger, more efficient, wing and 30% increase in fuel and commensurate increase in range. 
The larger fuselages of the -600, -700, -800 and -900 and their larger seating increases provided the bulk of the per seat fuel burn improvement between generations.
The 777X is already at the edge of 8,000nm performance, the design of the 777-9X need not stretch the aircraft’s legs beyond the current 777-300ER, but the new wing appears aimed at allowing the next generation 777 to accomodate an 12% increase in seats, additional revenue cargo coupled with a 15,000lb pull-back in maximum thrust.
The 737 Max, a fourth generation evolution of the narrowbody, works within the boundaries of the trans-continental performance already achieved with the wing of the Next Generation, pushing a design that comes to market faster, better and cheaper than its predecessor, rather than flying higher, faster, and farther.
Yet as Boeing works to firm the required investment to develop the 777X, the historical parallel with the Next Generation 737 signals an undeniable fact of aircraft development: As Boeing pushes its stalwart widebody design farther, each generational jump continues to be more expensive than the one that preceded. Answering this question is central to Boeing’s year-end go, no-go on the 777′s next generation.