Boeing has begun formal talks with airlines and leasing companies on the development of the 787-10X double-stretch derivative following the provisional go-ahead from the company’s board of directors.

The move is “conditioned upon our obtaining final board approval to launch the program at a yet-to-be-determined date,” says Boeing. Responding to questions from Aviation Week, the company adds, “The timing of a decision to launch the program will depend on market response during the next phase of our discussions about the airplane.”

The 787-10X is stretched by 18 ft. over the 206-ft.-long 787-9 to seat 43 more passengers. Targeted as an Airbus A330 “killer” with exceptionally low seat-mile costs, the 320-seater is expected to be a 6,700- to 6,750-nm-range aircraft with a maximum takeoff weight of about 551,750 lb., just under 7,000 lb. more than the 787-9 stretch now in initial assembly.

The 787-10X is being offered with the 78,000-lb.-thrust-rated performance improvement package (PIP) II standard General Electric GEnx-1B engine or the Rolls-Royce (R-R) Trent 1000 TEN (thrust efficiency new technology) version. Certification work on the PIP II engine, which includes a higher-flow, low-pressure compressor, improved high-pressure compressor and durability upgrades to the high-pressure turbine, is nearing completion, with icing tests about to begin.

R-R, which earlier this year signed a memorandum of understanding with Boeing to offer the Trent 1000 TEN on the stretch, is targeting introduction of the 787-8/9 in the first half of 2016. The engine will incorporate newer design features from the R-R Trent XWB now in development for the Airbus A350, and saves a further 3% fuel burn over the company’s current Package B standard.

Boeing adds that it has been “working closely with airline and leasing customers to define the key capabilities and features of the 787-10X, and we anticipate strong market demand for this third and largest member of the 787 family.”

Primary markets are expected to be on trunk routes from the Middle East to Europe and Asia, as well as transatlantic service, with British Airways and Singapore Airlines among early launch contenders. Assuming a firm launch decision later this year, entry-into-service is widely expected around 2018-2019.

Sources add that “nobody is using the word offerability at this point,” though the Boeing sales teams are now “allowed” to speak to airlines and present detailed marketing data for a product now deemed ready to move from product development to firm launch. Approval to offer is thought to have been given at the most recent board meeting, believed to have been held late last month.

The much-anticipated emergence of the 787-10X comes as Boeing wrestles with defining the configuration of its next major derivative program, the re-winged, re-engined 777X. Compared to the relatively straightforward double-stretch of the 787-10X, the development of a pair of larger successors to the 777-200LR/300ER for possible entry-into-service in 2019 is a far greater gamble in terms of cost, technology and marketing tactics.

Coming on top of the likely launch of the 787-10X, the timing of the next 777 development is pivotal to Boeing’s commercial strategy as the airframer weighs the threat of the upcoming Airbus A350 for the end of this decade and beyond. However, the size of the 787-10X is itself now thought to be playing a role in the outcome of Boeing’s 777X deliberations as it could feasibly cannibalize at least part of the intended market of the 777-8X, the smaller of the proposed 777X twins. Other resource-related factors playing heavily into the launch decision include Boeing’s already busy product-development plate, which is full with the on-going 737 MAX, 787-9 and KC-46A tanker programs, as well as the ramp-up of its production lines at both Everett and Renton, Wash.

It also comes as Boeing continues to accelerate 787-8 deliveries toward its year-end target of 35-42. Some 30 aircraft have been delivered to date, with as many as 18 more believed to be at or close to delivery readiness.