Aerospace consultant Richard Aboulafia, with the Teal Group, told Bloomberg that the pending deal "is a good endorsement" that the Boeing 737 redesign effort is "poised to achieve some kind of cost advantage."

But Richard Aboulafia of aviation consultancy Teal Group in Farifax. Va., and a longtime critic of the CSeries program, was blunt and severe. "Oh right, hooray! You fire everyone associated with the program, you have this unpleasant looking accident followed by a long unexplained silence (from Bombardier after May 29) and a nasty company re-organization. But hey, you're flying again. I mean, what the hell?" Aboulafia said "at this point, you can't rule out a total program failure."

Engine makers are accelerating production efforts amid a rise in aircraft purchasing by carriers seeking more efficient models. At a time when fuel represents the largest share of airline operating costs, improvements in under-wing technology have helped jets operate more economically, said Richard Aboulafia, an analyst at Fairfax, Virginia-based Teal Group. "It becomes essential to replace older, less-efficient jets with newer ones. They pay for themselves," he said."Every decade we get about 10 or 12 percent better. The meaning of that double-digit improvement is so much greater because of the high cost of fuel."

 That pressures Boeing to cut the wait for its new 737s, which can stretch to years for some airlines, says Teal Group analyst Richard Aboulafia.

The real problem is long-term," Aboulafia says, noting the record-high output for single-aisle airplanes over several years, with no slowdown until both the A320neo and MAX are in production. "Then you'll have Airbus try to exploit a first-mover advantage and Boeing working hard to ramp up faster and catch up. This all sounds like a recipe for overcapacity by the end of the decade."

But critics like Richard Aboulafia, an aerospace analyst at the Teal Group, an aviation-consulting firm in Fairfax, Va., say the main problem is more fundamental: Airbus made the wrong prediction about travel preferences.

He said people would rather take direct flights on smaller airplanes than get on big ones — no matter their feats of engineering — that make connections through huge hubs. "It's a commercial disaster," Aboulafia says. "Every conceivably bad idea that anyone's ever had about the aviation industry is embodied in this airplane."