Boeing's head of airplane developments said on Tuesday he was "very optimistic" that the world's largest planemaker would close the business for a new mid-market jet designed to open up new routes from the middle of the next decade.
Mike Delaney, general manager of airplane developments at Boeing Commercial Airplanes, said the final decision would be for Boeing's top leadership but that design, production and cost characteristics were all pointing in the right direction.
Speaking to Reuters, Delaney confirmed for the first time publicly that the proposed new aircraft would have a composite fuselage, a key decision likely to boost suppliers such as Boeing's sole composites contractor Toray of Japan.
In a separate briefing at the Paris Air Show, Delaney said the jet would make "extensive use" of composites and confirmed it would have a "hybrid" cross-section, apparently referring to the need for a large cabin and slimmed-down cargo space.
Delaney's keenly awaited annual briefing at the world's largest air show gave fresh clues on how the US planemaker's newest airplane might be designed.
The idea is to carve out a new market between medium-haul single-aisle planes like the 737 and Airbus A320 family and the smallest long-haul jets like the A330 and Boeing 787.
Boeing faces a difficult puzzle as it tries to square conflicting airline demands for a wide twin-aisle cabin with the low operating costs of the 737 category.
Delaney said airlines consulted by Boeing had stressed that what counts most is being able to carry the right number of passengers for the routes for which the jet is designed. Based on Boeing market forecasts that is likely to be 220 to 270.
They are less worried about carrying cargo.
That is the opposite of what airlines had said when Boeing was developing larger planes like the 787 and 777, Delaney said.
In those cases, engineers had designed the fuselage around the cargo containers and then adjusted the rest of the fuselage and therefore the seating capacity around that.
Delaney's statements give important clues about what is expected to be an unconventional fuselage for the mid-market plane, which in turn may determine whether Boeing can square that circle of wide cabins and low operating cost.
Industry sources have said the fuselage will have a somewhat elliptical shape when seen from the front because the bottom of the plane will be flattened to get rid of unnecessary cargo space.
Usually a pressurised fuselage is round to avoid stress points. Building the fuselage out of tough lightweight composites allows less conventional shapes.
In turn, stripping away unnecessary space reduces drag and makes the plane cheaper to fly.
Delaney declined to talk in detail about the design except to say the fuselage would have a "hybrid" cross-section.
"It is a geometry that supports twin-aisle comfort and single-aisle economics," he said.
Another Boeing executive recently said it had considered options from "mild to wild" for the new jet.
The new jet is expected to enter service in 2025, if Boeing decides to go ahead and develop it.