Of course, the Model T was successful too: that doesn't mean its success enabled Ford ( F) to stop innovating.

It is customers who drive commercial innovation, notes Saj Ahmad, aerospace/airline analyst for FBE Aerospace in London. "Boeing has plenty of customers in Europe like Ryanair and in the Middle East like FlyDubai who are just two of many big 737 customers who could push the move to a new jet," Ahmad said.

And while Boeing has been working with engine makers on 737 improvements, "the resources required to close the business case on re-engineering is starting to appear less compelling in contrast to an all new narrowbody solution," he said. "From a capital expenditure point of view, it makes more sense to create a clean sheet design to leverage the benefits of these new fuel efficient engines." Boeing's decision is more likely to be driven by its customers than by an effort to respond to competitor Airbus, he added.

Still, Hamilton said Boeing's consideration of a new aircraft raises a host of questions. "One of the concepts is a small twin aisle aircraft, with 2X2X2 seating: another is widening the fuselage to be like the A320 to give more space," he said. Others: Would the plane be built primarily of composites, or of a lighter aluminum? And where would it be built?

Production could begin in five years, Hamilton said. Throughout that period, it is safe to say, development of the Boeing 838 -- if that is what the new airplane is called -- would be among the most closely watched stories in aviation.

-- Written by Ted Reed in Charlotte, N.C.

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