Airbus and Boeing need to increase output of narrowbody jets to burn off massive backlogs, but lofty production rates the two airframers are talking about probably cannot be sustained over the long run, says the CEO of U.K.-based aerostructures suppliers GKN Aerospace.

“The narrowbodies are going to have to ramp up,” Kevin Cummings said in an interview with Aviation Week at the Paris air show June 17. “I don’t believe that Boeing and Airbus want to have a customer come in the door and tell them "you have to wait nine years" for delivery."

Output of Airbus A320s and Boeing 737s currently stands at 42 per month each. Airbus plans to take production up to 50 a month by early 2017 and says it could go as high as 63. For its part, Boeing plans to raise 737 production to 52 per month by 2017 and says it could easily ramp up to 60.

But could the market really absorb 120-plus narrowbodies a month over the long term? Cummings is skeptical. “Will orders stay at 2014 levels?” he asks. “We’d love to see that, but when you look at GDP growth and other indicators, that type of order input can’t keep coming.”

And therein lies the dilemma for suppliers. Do they make big investments in equipment, facilities and workers to support higher production rates that might only be temporary? “We need to support our customers,” Cummings says. “But how do we do that realizing whatever investment we have to make to get there could potentially not have a long-term run.”

Teal Group analyst Richard Aboulafia, in a column written for the June 22 edition of Aviation Week & Space Technology, also believes that the market cannot absorb the number of A320s and 737s that Airbus and Boeing are talking about over the long run. “Supplier companies should beware,” Aboulafia says. “There is a very real risk that they will be stuck with overcapacity and higher fixed costs if the market turns down when output of 1,500 single-aisle deliveries per year proves to be unsustainable.”

But Cummings puts a positive spin on the challenge.  “This is a good problem to have,” he says. “It’s a problem I’m okay facing.”