(Bloomberg) -- United Airlines Holdings Inc. will buy 110 more aircraft that will be delivered starting in five years, extending its aggressive bets on growth and future travel demand.

United converted existing options it held into firm orders on Tuesday for 50 Boeing Co. 787-9 Dreamliners, to be delivered from 2028 through 2031, and for 60 Airbus SE A321neos for delivery between 2028 and 2030. The planned double-digit purchase of Airbus jets was reported earlier by Bloomberg. 

The Chicago-based airline also secured new options for additional planes at the end of the decade, it said in a statement.

United has been one of the largest aircraft buyers this decade and has said it plans to add about 800 narrow- and widebody planes over the next ten years or so as it hires more than 10,000 pilots. The latest purchases build on a multibillion-dollar deal with Boeing for 100 planes and the option for 100 more that was placed in December.

“I’m convinced our strategy is the right one as we continue to add new, larger aircraft to take full advantage of our growing flying opportunities both internationally and domestically,” Chief Executive Officer Scott Kirby said in the statement. 

Carriers across the world are locking in delivery slots for new aircraft as Airbus and Boeing struggle to keep pace with demand spurred by a rebound in air travel. Backlogs at both planemakers now stretch past the end of this decade, and United’s latest orders are a bid to ensure a steady flow of aircraft.

Among single-aisle planes, United now has 180 A321neos and more than 370 737 Max aircraft on firm order through 2030. The airline’s strategy is to fly larger planes with more seats on existing routes. It’s planning to average more than 145 seats per North American departure in 2027, up from 104 in 2019, the carrier said. 

That’s aimed at reducing costs to fly each seat a mile, a gauge of efficiency, and designed to allow United to carry more passengers to its hubs. 

The carrier also has the most twin-aisle Dreamliner orders at 150, Boeing said in a statement. 

The airline also secured options Tuesday for up to 50 more 787s and an additional 40 A321neos at the end of the decade.  

The A321 has emerged as the most popular variant in Airbus’s single-aisle lineup, with a backlog of over 4,200 jets. The model can seat as many as 240 passengers. United also has orders for an extra-long range variant of the A321 that’s currently in development. That plane will be capable of flying non-stop from New York to Rome.

(Updates with total aircraft on order in seventh paragraph)

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