LYNNWOOD — Is the commercial airplane industry’s historically large order backlog legitimate or a bubble waiting to burst?

That question kept coming up on the opening day here of Washington’s largest annual aerospace conference. Industry insiders — from analysts to airline executives to suppliers to airplane makers — responded all but unanimously: There’s probably not a bubble, but there could be.

Economic bubbles are prone to burst, sometimes forcing violent market realignments that can consume companies, swallow individuals’ investments and drive up unemployment.

The huge order backlog — most of which is for jetliners made by the Boeing Co. and Airbus — is unusual enough to worry some in the aerospace industry. Their concern is that the airlines that placed the airplane orders could cancel or delay them, which would send a ripple through the industry.

“The foundation for everybody’s health in this industry is the airlines,” said David Fitzpatrick, an aerospace analyst with AlixPartners, based in San Francisco, during a panel at the Pacific Northwest Aerospace Alliance’s annual conference.

Fitzpatrick is not worried about a bubble, though.

He pointed to improving global economic conditions, airlines reducing the number of empty seats on planes and the need to replace aging aircraft as some of the reasons that demand for new planes isn’t going to burst.

“You should invest in this industry. There’s growth here,” he said.

There might be some “irrational exuberance” in some of the orders, but “have faith in the future — no bubble,” Fitzpatrick said.

Forget faith, there’s a bubble coming, said David Strauss, an analyst with UBS.

Strauss was the only speaker to take such a dim view of the industry’s next few years.

Air traffic isn’t growing fast enough, and airlines are keeping older planes in service too long to support the supply of new airliners, Strauss said.

Analysis by UBS indicates the oversupply of commercial airplanes will be big enough to start driving down production rates by 2016.

If UBS is right, that means there’s a bubble and it will burst — or at least start deflating — in a couple years.

Boeing doesn’t appear concerned. On Tuesday, the company announced that it is increasing the 737 production rate to 42 planes a month at the Renton plant.

The Chicago-based company will likely increase production further in coming years, according to Boeing.

Airbus will likely match Boeing’s production rate as the two fight each other and new entrants in the single-aisle jetliner market, said Scott Hamilton, an aerospace analyst with Issaquah-based Leeham Co.

The current order backlog for narrow- and wide-body jets is so big that even “if you cancel 10 percent, what does it really matter?” Hamilton said.

The PNAA conference continues through Thursday at the Lynnwood Convention Center.

Dan Catchpole: 425-339-3454; dcatchpole@heraldnet.com.