Boeing on Wednesday detailed how it plans to accommodate larger and heavier engines on the forthcoming 737 MAX while meeting ambitious fuel-efficiency goals.

The MAX, an update to its single-aisle workhorse jet, features new, more-efficient engines from CFM International that will require various structural changes to the airframe. Boeing said it will add an 8-inch extension to the nose landing gear, lifting the airplane so the larger engines will have ground clearance similar to today's 737s.

Boeing will also extend the jet's tail cone and thicken a section of the rear fuselage above the horizontal tail to improve air flow and reduce drag.

And it will strengthen the main landing gear, and parts of the wing and fuselage, because of the heavier engines.

In addition, Boeing has decided to save weight by putting fly-by-wire rather than mechanically controlled spoilers on the wings. The spoilers are flight-control surfaces used to disrupt air flow and reduce lift as the plane approaches a landing.

The MAX program has already snagged 451 firm orders, with 135 other announced commitments. Boeing Commercial Airplanes chief Jim Albaugh has said he expects to have around 1,000 firm orders by year-end.

But airlines have been awaiting details to see how Boeing proposes to achieve its target of 16 percent better fuel efficiency than Airbus' current rival jet, the A320.

An airline executive, speaking on condition of anonymity, said the perception is that "Boeing is really struggling with the MAX" and has a long way to go to attain the projected fuel-efficiency improvement, which is needed to match the performance promised by Airbus' forthcoming update, the A320neo.

In a statement, Beverly Wyse, vice president and general manager of the 737 program, insisted the MAX is "on track."

And Michael Teal, 737 MAX chief project engineer and deputy program manager, said the design work and preliminary testing give officials "even more confidence" in the efficiency projections.

Still, the design won't be completely finalized until mid-2013.

Boeing said engineers are now doing wind-tunnel tests to assess a possible change to the shape of the MAX wingtips.

Dominic Gates: 206-464-2963 or dgates@seattletimes.com

Logistics facility

for Dreamlifter planned

Boeing plans to build a large logistics facility on the northwest corner of Paine Field in Everett for its fleet of giant Dreamlifter transport jets used to transport 787 subassemblies from Japan, Italy, Wichita, Kan., and North Charleston, S.C.

The jet-maker needs a facility of approximately 30,000 square feet, and the airport has identified a potentially suitable location just south of the Future of Flight building, between the runway and Paine Field Boulevard, known as "Kilo North."

A person familiar with the details said the building will store jigs, fixtures and tools associated with the Dreamlifter loading and unloading operations, as well as equipment and parts used to maintain the Dreamlifters.

The Dreamlifters will not be kept in the new building, and unloading operations should take place outside.

Boeing paid for the design and engineering of the building.

The county will pay to build it, then lease it back to Boeing, which is a typical arrangement for businesses around Paine Field.

Construction is expected to begin by late summer, said Snohomish County spokesman Christopher Schwarzen.

— Dominic Gates