Boeing 737 MAX design changes include accommodating larger engine, lengthening nose landing gear.

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Boeing has nailed down some key design details for the forthcoming revamp of its single-aisle jet, the 737 MAX, including the crucial fan diameter of the more fuel-efficient engine that will power the jet.

The company released the new details Thursday to try to stem the momentum of the hot-selling A320neo, Airbus’ revamp of its single-aisle jet family that features an even larger new engine.

The current models of the Airbus A320 and the Boeing 737 split the single-aisle market roughly down the middle. Boeing needs the MAX to maintain that share against the neo.

In a teleconference with journalists, John Hamilton, the 737 chief project engineer, said the current 737 is lighter and more fuel efficient than the current A320, and the new MAX design will leapfrog the neo and have 7 percent better operating economics.

“There’s a much better structural efficiency that goes into the 737 design than into the Airbus design,” Hamilton said.

He said Boeing will increase the engine fan size from 61 inches on today’s 737 to 68 inches on the new MAX engine — called the LEAP, being developed by CFM International.

A bigger fan sucks in more air, providing greater thrust. But Boeing’s increase in engine fan size just matches the fan size of today’s A320.

The forthcoming A320neo engine will be even larger, with a choice between a version of CFM’s LEAP with a 78-inch fan and a Pratt & Whitney geared engine with an 81-inch fan.

Hamilton took pains to explain that while size matters, it isn’t everything.

The 737 is lightly smaller and lighter than the A320. And a bigger fan size, while providing more efficient propulsion, increases weight and drag.

“Today, our (737) engine is 7 inches smaller than the Airbus (A320) engine, and yet we have lower operating costs,” Hamilton said. “The 737-900ER is nearly 50 pounds lighter per seat” than the comparable A321.

The MAX “doesn’t need the high thrust requirements that the Airbus product has,” he said. “When you look at drag, fuel efficiency and weight, the 68-inch fan is really the optimum solution for the 737 airplane going forward.”

Airbus disputes Boeing’s assertions of an operating cost gap between the two current models.

But the even sales split makes clear the two airplanes are roughly matched in customer appeal. So Boeing’s contention that the MAX can leapfrog the neo even with a smaller-size engine could make sense if its engineers get the overall design right.

Along with the new engine, Boeing will refine the 737 airframe design in relatively small ways without changing the overall size of the planes, Hamilton said.

The larger, heavier engine will necessitate strengthening of the wing and parts of the fuselage, as well as designing a heftier strut to hold the engine on the wing and making minor system changes. Boeing will also lengthen the nose landing gear to raise the wing slightly and reshape the tail cone to streamline the air flow.

And it will introduce fly-by-wire spoilers — the hinged parts on the wing that rise on landing to increase drag — which means they will be operated by computer rather than by direct cable connections.

Boeing maintains that overall the 737 MAX will be 4 percent more fuel efficient than the A320neo and will have 7 percent lower operating costs.

Airbus spokeswoman Mary Anne Greczyn dismissed that claim, saying Boeing is struggling to overcome a structural limitation: that the 737 wing sits closer to the ground than the A320’s wing, so that a larger, more fuel-efficient fan won’t fit.

“If a smaller fan engine were to generate the appropriate level of efficiency, we could have easily incorporated that, since we are not constrained as our competitor,” Greczyn said. “The A320neo family is designed to benefit from the aircraft’s inherent advantage.”

Boeing launched the 737 MAX in August; Airbus launched the neo last December and by the summer had captured more than 1,000 orders from airlines eager for more fuel-efficient planes.

The neo, due to enter service in 2015, at the end of September had 918 firm orders plus an additional 319 purchase commitments.

The MAX, scheduled to enter service in 2017, has no firm orders. But on Thursday Boeing said it has garnered 600 purchase commitments from eight airlines, including some U.S. carriers.

Hamilton said customers are “responding well” to Boeing’s preliminary design and that he expects “several hundred more commitments soon.”

Boeing won’t finalize the design until 2013, he said.

A big question for this region is whether Boeing will continue to build the MAX in Renton, where the 737 is assembled today.

Boeing executives say they will decide by the spring. Company spokeswoman Karen Crabtree said Thursday that the Renton site “has the skill base and knowledge to incorporate the production changes” needed for the MAX.

Dominic Gates: 206-464-2963 or

747-8 freighter deal

dead; switch to 777s

Dubai airplane lessor DAE Capital has canceled five orders for Boeing’s new 747-8 jumbo jet freighter, Boeing announced Thursday. DAE instead will take five 777 freighters that will be operated by Dubai’s successful government-owned carrier Emirates.

The switch cuts the already small 747-8 order book to just 106 airplanes. The slightly cheaper 777, meanwhile, is selling better than ever, with 134 orders so far this year.

Five 747-8Fs are worth $1.6 billion at list prices, though aircraft-valuation firm Avitas estimates the real amount after standard discounts at $953 million.

Five 777Fs are worth $1.3 billion at list prices, with an Avitas-estimated value after standard discounts of $810 million.

The financial crisis of 2008 slammed Dubai’s overheated real-estate market and sank the investments of the backers of DAE Capital, which was managed until the summer by a group of seasoned airplane-leasing executives from the Seattle area, led by CEO Bob Genise.