Amid increasing industry speculation about the imminent launch of re-engined narrowbodies, Flightglobal has learned how Boeing could engineer the tricky installation of an advanced turbofan under the wing of the 737.
To provide additional clearance under the wing to accommodate a larger engine nacelle, Boeing is examining the feasibility of raising the 737's nose landing gear, say industry sources. According to those familiar with the plan, an extension of the nose landing gear of 15cm (6in) would yield an estimated 5cm of additional diameter in the fan.
One internal industry assessment of the feasibility of a re-engined 737 seen by Flightglobal says that the aircraft can currently handle a 1.6m fan without any modification.
A new engine with a 1.6m fan would yield an approximate 12% improvement in specific fuel consumption, before any other airframe modifications are incorporated says the assessment. An engine with a 1.7m fan combined with a "modest increase" in landing gear height would yield fuel burn similar to a re-engined Airbus A320.
Any increase in the length of the nosegear is likely to require a larger wheel well, and by extension would reduce space available in the aircraft's forward avionics bay.
It was once believed that extending the 737's main landing gear would provide the required clearance. However, increasing the size of the main landing gear would yield a significant weight increase and complicate stowage.
Boeing Commercial Airplanes vice-president marketing Randy Tinseth recently confirmed to Flightglobal that Boeing had competed a successful technical feasibility study into the installation of a new engine on the 737, but that the modification would require "a lot of work".
The leading candidates for the re-engining are CFM International's Leap-X advanced turbofan and a possible offering from International Aero Engines that is likely to be based on partner Pratt & Whitney's geared turbofan.
P&W's commercial engines senior vice-president sales Bob Keady says that IAE is the "preferred route to market" for new engine offerings for either Airbus or Boeing single-aisle aircraft, but adds that P&W has been "doing some work" with both airframers about installing the GTF on their existing aircraft.
"We think we can have an effective installation of the GTF on the 737," he says.