Boeing chief executive Ray Conner used a pre-Paris air show briefing to offer new insights on technical details of the 777X and 787-10 - but was unwilling to answer the biggest questions swirling around the widebody programmes, such as their launch dates and respective supply chains.
The airframer is widely expected to launch the 787-10X and possibly even the 777X during the show, but the latter is vaguely described as a longer-term decision in discussions with company executives.
The 787-10X adds 5.49m (18ft) and around 30 seats to the fuselage of the 787-9, which is itself a 6.1m and 40-seat stretch of the 787-8.
While Boeing describes the double-stretch as mostly "straightforward", the 73.8m overall length of the new aircraft will require certain changes.
Conner says the 320-seat 787-10 does not require a six-wheel bogey on each main landing gear as does the 350-seat 777-300ER, but it will borrow the latter's semi-levered gear. By tilting upward upon take-off such a gear increases the maximum rotation angle, which helps avoid tailstrikes on such a long fuselage.
At the same time, Conner dodged answers to some of the hardest questions about the 787-10X, such as whether the aircraft will be assembled in Everett, Washington, and if Boeing will increase the production rate beyond the 10-per-month goal for later this year.
Conner was even less forthcoming on questions about the 777X, the project that includes the 400-seat, 8,000nm-range 777-9X and the 350-seat, 9,500nm-range 777-8X. The 777X models should offer a 20% fuel burn improvement over the 777-300ER by using a composite wing and the General Electric GE9X turbofan engine, Conner says.
But he concedes the new aircraft will suffer a small weight penalty compared with the composite fuselage of the 350-seat Airbus A350-1000. Boeing has ruled out switching to a composite fuselage, as it does not wish to recapitalise the supply chain of the 777. Boeing is considering using stronger and lighter aluminium-lithium metal instead of aluminium-only in the fuselage, Conner confirms.