As it moves closer to a decision on re-engining the 737, Boeing Commercial Airplanes CEO Jim Albaugh says his company must resist the urge to modify the 737 too much.
"You've got to watch out for the requirement creep. Our engineers would love to put every bell and whistle on this airplane that they know of, we have to resist that," says Albaugh.
"I will do everything I can to reduce the requirements creep, so it doesn't become an equivalent of a major change to the aircraft, and we certainly don't want it to become a new airplane. When we do a new airplane we want to bring the right technologies to it, which will really give us a leap over what we've built today."
For example, adding 787-style avionics and flight deck to the 737, while potentially desired by Boeing's customers, would serve to drive up the development cost and price of the re-engined aircraft.
"It's really driven by the technology that's available and can you close the business case for a re-engining," says Albaugh.
Other issues to consider include how long a production line would be in place for a re-engined 737 and then also understanding when new tehcnology might come along that "would really drive you towards a new airplane".
Albaugh adds that the re-engining question is a "very complex algorithm" that takes into account the dispatch reliability of an existing airframe with a new engine, as well as any maintenance implication of airlines introducing of a new 737 model along side Next Generation and Classic 737s, as would be the case with Southwest Airlines.
"It's not as easy to just say, you can get 10-15% efficiency, let's go do it," he says.
"One thing I've learned that there's nothing simple about a derivative airplane. There's certainly nothing simple about a re-engine. If you did a re-engine the pylon would change, the empennage would change, you'd have to raise the front gear a little but, drive some different loads into the airplane, drive some different loads into the wing."
Additionally, Boeing has begun wind tunnel tests on various designs for a re-engined 737, evaluating the aerodynamic characteristics of a larger engine, as well as a modified strut and pylon.
Albaugh says he holds weekly Friday meetings to discuss the progress on the re-enginging studies.
Boeing expects a re-engining decision to come in the latter part of this year.