Uncertainty over a Boeing jet and apprehension about the global economy hover over the aircraft industry as the Paris Air Show got underway Monday.

That show and its alternating-years companion, the Farnborough International Airshow near London, are usually upbeat celebrations of the latest and greatest in aviation technology. In recent boom years, they have become a stage for huge aircraft orders.

This year, the mood could be different.

The Boeing 737 Max has been grounded worldwide for three months after new flight software played a role in two deadly plane crashes. There is no clear date for when it might fly again.

There are other troubling signs for the industry. After several years of surging growth, passenger traffic in March grew at the weakest rate in nine years, although April was slightly better. The chief of the International Air Transport Association, a global airline trade group, blamed a slowing global economy and damage from tariffs and trade fights.

Air cargo shipments — considered a leading economic indicator — fell 4.7% in April, continuing a slump that began in January and could dent demand for air freighters.

And airlines have committed to buy so many planes that Boeing now has a backlog of 5,500 orders and Airbus has 7,200 — far higher than usual. Airlines might not have much appetite for more.

"There is a lot to be concerned about," said Richard Aboulafia, an aerospace analyst with Teal Group. "It might make for kind of a grim Paris."

Boeing announced lackluster orders on the opening days of the show, while Airbus announced a bevy of new sales and launched a new long-range single-aisle jet, beating its U.S. rival to a market that both aviation giants predict will grow.

The two companies have reported much weaker orders this year. Boeing received no orders in May after getting just one in April. Deliveries of completed jets tumbled 56% last month as it stopped shipping new Max jets. Airbus saw an increase in deliveries, but it reported just one new order last month.

Airlines have placed so many orders for the Boeing 737 and Airbus A320 family already that analysts expect few new sales for those so-called narrowbody planes this week.

Credit Suisse analysts predicted that no airline will order any more 737 Max jets until the grounding is lifted.

"I do believe that that aircraft will get back in the air and commercially minded airlines will buy it, but just not next week," said Samuel Engel, a senior executive at the airline and aircraft-finance consultant ICF.

He said public doubt and fear about flying on the plane is too great right now but — and this is a view widely shared in the industry — will diminish over time.

The Max, the newest version of Boeing's best-selling plane, is critical to the company's future. The Max was a direct response to Airbus' fuel-efficient A320neo. Airbus has taken 6,500 orders for various neo models, outpacing the Max with its nearly 5,000 orders.

Boeing has struggled to get a handle on the Max controversy. Its fix for software implicated in crashes that killed 346 people has taken months longer than expected, and it is unclear how long it will take the Federal Aviation Administration and other regulators to approve Boeing's work.

The acting head of the FAA has faulted the company for not telling regulators for more than year that a safety indicator in the Max cockpit didn't work. Pilots were furious that the company didn't tell them about the new software on the plane.

CEO Dennis Muilenburg acknowledged "mistakes" on Sunday, saying Boeing's communication with regulators and the the public "was not conistent. And that's unacceptable." 

Airbus executives said the Max crashes didn't affect their own strategy for the air show.

"What has happened with the Max ... doesn't change the way to talk to customers," Airbus CEO Guillaume Faury said.

Media coverage of the annual air show often boils down to who logs the most sales, Boeing or Airbus.

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"Airbus tends to stockpile or hold on to orders to announce at the air show, so I would certainly expect more activity out of Airbus than Boeing" in Paris, said Ken Herbert, an aerospace analyst for Canaccord Genuity. "I don't think that will surprise anybody, considering the Max and everything else."

Herbert said if Boeing can just make "a decent to good showing" in orders for its bigger "widebody" planes, the 777 and 787 — it makes the latter in North Charleston and Everett, Wash. —  the event will be deemed a success for the Chicago-based company.

Airbus used the air show to officially launch a new plane, the A321XLR, a long-range version of its popular A320 family, which could set off several plot twists in the competition between Boeing and Airbus.

Airbus also annocuned its first order for a new longer range model — Air Lease Corp. is buying 27 of the new jets.

American Airlines is considering the plane as a replacement for its fleet of aging Boeing 757s, according to Bloomberg. A spokeswoman for American declined to comment.

If a U.S. carrier like American — the biggest in the world — steps forward as an early buyer of a plane from Boeing's European rival, it will make a big splash.

Airbus executives wouldn't comment on American or other potential customers.

Monday's announcement about the new plane could send ripples into the board room at Boeing headquarters. Boeing is considering whether to build a new jet — the concept is dubbed "New Midsize Airplane," or NMA — that would be close in size to the A321XLR. It would fill a gap in the Boeing lineup between the smaller 737 and the larger 777 and 787 Dreamliner.

Some analysts believe that if American orders the A321XLR, it will give Boeing more incentive to push ahead with the NMA rather than surrender a portion of the market to Airbus.

The long boom for aircraft manufacturers has already lasted longer than expected. The Paris show could tell whether airlines are optimistic enough about the economy and travel demand to keep buying, even though new orders so far in 2019 have been anemic.

"If people are going to trot out orders, it's here," Aboulafia said. But, he added, "We are in year 15 of a seven-year cycle."

Angela Charlton of the AP contributed to this report.