Pratt & Whitney and CFM might not like to hear it, but if the assertions of Boeing CFO James Bell prove accurate, the 15- to 16-percent fuel efficiency gains the engine makers have repeatedly advertised for their respective next-generation turbofans will translate into less than double digits if and when they make their way onto existing narrowbodies. Consequently, chances that Boeing will fit new engines on today’s Boeing 737 appear slimmer now than at any time since the company began talking publicly about the idea.

Speaking last month at the Morgan Stanley Industrials Unplugged Conference in New York, Bell went further than any Boeing executive to date in throwing a proverbial bucket of cold water on the idea of a re-engined 737. Although in July Boeing CEO Jim McNerney said that “on balance” Boeing’s customers would rather see a completely new design, it was not until Bell said at the New York conference, “I can tell you our customers have not shown a real interest in a re-engining,” that the prospects for a re-engined 737 have appeared so remote.

“Right now it looks like the engines can get 10- to 15-percent more efficient, but it’s not flow-through efficiency,” Bell explained. “When you add the weight associated with the change in the design of the airplane and you add the cost, it looks more like a single-digit improvement, which we don’t believe is something that our customers are interested in.”

Although his words sounded rather definitive, Bell wouldn’t completely discount the possibility of a re-engining, particularly if fuel prices surge by the time the company decides on plans for the future of the 737. Still planning to choose by the end of this year among the options of re-engining, introducing an all-new airplane or improving an existing airframe, Boeing has yet to finish its studies, said Bell.

“On the new airplane, we obviously are looking at what are the technological improvements that we need to have in order to [achieve] flow-through improvement of 10- to 15 percent,” he added. “At this point we don’t know exactly what that is. We do know part of it would be the engine. The other part would have to be improved aerodynamics of the aircraft itself. It’s easier to scale up [composite material] than scale it down, but we’re still working at it.”

To some extent, Bell’s comments echo those made by Rolls-Royce head of strategic marketing Robert Nuttal back in July at the Farnborough airshow. Nuttal told AIN that “the numbers do not stack up” for re-engining either the A320 or the 737.
Rolls believes the case for re-engining the existing narrowbody families is flawed on three scores: first, there would be insufficient financial benefits to airlines; second, it would take engine makers only twice as long to develop entirely new powerplants; and, finally, the effort involved in re-engining could actually delay the eventual introduction of completely new aircraft, which would offer far greater fuel savings.