New Pilots

Boeing Defines 737 MAX "Extra Stretch"

2017 01 11

Boeing has defined the size of the proposed additional -10X stretch variant of the 737 MAX narrowbody to compete more aggressively against the Airbus A321neo.

Boeing, which first revealed design studies of an extra stretched variant of the MAX in mid-2016, has finalized a design based on a 66-inch fuselage stretch. While significantly less than the 132-inch extension it outlined at the 2016 Farnborough Air Show, the additional cabin length enables two-class capacity to be increased to 189 passengers, compared to 193 for a similarly configured A321neo. In a single class, the -10X could seat up to 230.

The minimal change in design is expected to be both cheaper and faster to develop than more extensive stretch options evaluated earlier in 2016. The modest stretch enables Boeing to retain the existing wing and CFM Leap 1B engine, rather than having to adopt a more extensively reinforced wing structure and larger Leap 1A/C variant considered under earlier studies. The reduced scope of the design changes also means the company will be able to offer the -10X for entry into service as soon as 2020, giving the aircraft longer to compete against the A321neo and dovetailing into the current new product introduction sequence that starts with the debut of the 737-8 later this year.

"We are looking at an airplane which doesn't need extra thrust and requires less of a stretch, which is advantageous from a weight and drag perspective," Boeing Commercial Airplanes VP & general manager, airplane development, Mike Delaney said in late 2016. "This preserves the economics of the 737 and is better for customers that want to have a mixed fleet because they have the same engine."

However, even though the engine remains the same, Boeing will have to incorporate a modified main landing gear design to enable adequate clearance of the longer body for rotation on takeoff and landing and to ensure the aircraft remains stall- rather than pitch-limited. The additional fuselage stretch will extend the overall length of the -10X to just over 143 feet compared to 138 feet 2 inches for the 737-9. Having previously sought options for installation of a taller main landing gear without the need and expense of moving the pivot point of the leg, Boeing is adopting a form of trailing-link gear design that shifts the rotation point slightly aft.

Although the manufacturer studied various multi-hinged and compressible oleo designs for the earlier configurations, the trailing-link feature is believed to be considered simpler and less maintenance-heavy. The new configuration will be conceptually derived from the semi-levered main landing gear design developed for the 777-300ER. The gear system enables the longer-range 777 version to rotate about an axis of the set of aft wheels rather than a central point of the three-axle bogie beam where the main strut is located. Boeing plans to adapt a version of the leveraging mechanism to the existing single-axle strut of the 737.