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Airline to Operate World’s Largest Mainline Fleet in 2025

United Airlines to Operate World’s Largest Mainline Fleet in 2025
United Airlines is set to become the operator of the world’s largest mainline fleet in 2025, according to recent data from ch-aviation. In the airline industry, "mainline" refers to aircraft operated directly by the carrier itself, excluding those managed by regional subsidiaries or alliance partners. With a fleet expected to exceed 1,000 aircraft, United will surpass its closest rivals, American Airlines and Delta Air Lines, solidifying its position at the forefront of global aviation.
United’s Expansive and Diverse Fleet Composition
United Airlines plans to field a mainline fleet comprising 1,056 aircraft, collectively offering nearly 250,000 seats. The airline’s widebody operations are anchored by the Boeing 777-200ER, with 55 units in service. Its narrowbody fleet is even more substantial, featuring over 100 aircraft each of four Boeing 737 variants, including the 737-800, 737-900ER, and the newer 737 MAX 8 and MAX 9 models. The airline has also retired older 737 models and the iconic Boeing 747-400, replacing them with more fuel-efficient aircraft such as the 737 MAX series, with 167 MAX 10s currently on order.
The fleet’s average age stands at 16.9 years, reflecting a balance between mature aircraft and newer additions. Key widebody aircraft include 47 Boeing 787-9s averaging 6.6 years in service, 37 Boeing 767-300ERs at nearly 30 years old, and 21 Boeing 787-10s with an average age of 5.4 years. On the narrowbody side, the Boeing 737-800 and 737-900ER fleets number 141 and 136 respectively, while the 737 MAX 8 and MAX 9 variants total 236 aircraft combined. United also operates 81 Airbus A319-100s, rounding out its diverse narrowbody lineup.
Competitive Landscape and Operational Challenges
Delta Air Lines currently holds the position of the second-largest mainline fleet, predominantly composed of narrowbody jets. Delta’s fleet includes 158 Boeing 737-900ERs, 127 Airbus A321-200s, and 84 A321neos. Its widebody fleet is comparatively smaller, with 39 Airbus A330-900s and a similar number of Boeing 767-300ERs.
Operating the world’s largest mainline fleet presents significant challenges. Airlines continue to grapple with aircraft shortages and intense competition, as underscored by ANA Holdings’ recent mid-term strategy. Market volatility remains a pressing concern; for instance, British Airways’ parent company, IAG, experienced a negative market reaction to its third-quarter earnings due to softness in yields and load factors. Competitors are adjusting their fleet strategies accordingly—Wizz Air, for example, has scaled back its Airbus A321XLR commitments and delayed deliveries.
Furthermore, the U.S. airline industry remains vulnerable to external disruptions such as government shutdowns, which can impede operations and affect financial performance. Managing a fleet of this magnitude demands agility in responding to shifting market conditions, supply chain constraints, and evolving passenger demand.
Outlook
As United Airlines prepares to lead the industry in mainline fleet size in 2025, its capacity to navigate operational complexities and market fluctuations will be crucial. The airline’s ongoing efforts in fleet modernization and strategic planning will be instrumental in sustaining its competitive advantage amid a rapidly evolving aviation environment.

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