Star Alliance carrier United Airlines has extended its lead as the world's largest airline in terms of fleet size with the historic delivery of its 1,000th aircraft. The Boeing 737 aircraft was delivered this week, making the carrier the first airline worldwide to operate more than one thousand planes.
A shiny new MAX 9
The Boeing 737 MAX 9 aircraft (registered N77584) was successfully delivered on Monday and is scheduled to fly to Seattle-Tacoma International Airport (SEA) from King County International Airport, commonly known as Boeing Field (BFI), later this afternoon. According to data from Flightradar24, the narrowbody passenger jet is due to take off shortly after 13:00 and land at SEA bearing the flight number UA3849.
United Airlines Made $3.5 Billion Last Year Flying More Passengers Than Ever
United Airlines' CEO remarked that 2024 was a strong year, with demand trends in 2025 continuing to accelerate.
The plane previously flew on Friday, January 24th, for what appears to be the customer acceptance flight. Aircraft tracking data shows the plane departing Boeing Field at 11:48 and flying west across Olympic National Park to reach the Pacific Ocean before turning back and flying across southern Washington State and northern Oregon before circling Boeing's Moses Lake facility and returning to Seattle at 14:16.
The aircraft is powered by CFM International LEAP-1B engines and features 20 seats in United First and 159 in economy, split between United Economy Plus and standard economy seats. The plane is the fourth in a multiple-aircraft sale-leaseback agreement between Aviation Capital Group and United Airlines.
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The aircraft will help support operations as United Airlines, which is introducing a range of new and unique destinations this year, including Ulaanbaatar, Mongolia; Kaohsiung, Taiwan; Palermo, Italy; Bilbao, Spain; Madeira Island and Faro, Portugal; Dakar, Senegal; and the new Nuuk Airport in Greenland.
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With more aircraft on the way, United aims to surpass 1,000 active aircraft and become the largest airline in the world.
According to the airline, it will fly to around 360 destinations this summer, including 800 daily flights to and from 147 international destinations. Including the recently delivered plane, United Airlines expects to receive 10 widebody jets and 71 narrowbodies. The airline still has around 680 aircraft on order for deliveries through the end of the decade, including 40 leased Airbus A321neos.
Where do the other airlines stand?
United Airlines is the only airline in the world to reach the milestone of having 1,000 aircraft in its fleet, although its planes are not necessarily active. When Simple Flying reached out for comment this morning, an airline spokesperson confirmed that the carrier had taken delivery of N77584 as its 1,000th aircraft but declined to provide any additional comments.
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Based on data from Aviation Flights, United Airlines may expect to take delivery of another new aircraft in the coming days. Two potential customer acceptance flights have occurred over the past few days for a Boeing 737 MAX 8 registered N17359.
The Top 10 Passenger Airlines With The Largest Fleets In The World Ranked By Capacity
The big four US-based airlines continue to have the most capacity in the world, while many of the other top airlines are in Europe and Asia.
The following two largest airlines in terms of fleet size are also US carriers. According to the latest available data from ch-aviation, oneworld Alliance carrier 
American Airlines is the next closest to reaching 1,000 airplanes. The airline has 997 aircraft in its mainline fleet and more than 320 on order.
Close behind is 
Delta Air Lines, which, based on data from planespotters.net, has approximately 985 planes in its mainline fleet. Much like American Airlines, Delta has around 300 jets still on order for its mainline fleet.