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Which Narrowbody Aircraft Is United Airlines the Largest and Only U.S. Operator Of?

United Airlines: The Largest and Sole U.S. Operator of the Boeing 737-900
In the realm of narrowbody aircraft, United Airlines holds a distinctive position as the largest and soon-to-be only U.S. operator of the Boeing 737-900. This model, part of Boeing’s 737 Next Generation (NG) family, was introduced as a stretched variant of the widely used 737-800, designed to rival the larger Airbus A321. However, the 737-900’s limited exit configuration restricted its maximum seating capacity to 189 passengers, a constraint that diminished its appeal among low-cost carriers aiming to maximize passenger numbers. Consequently, only 52 units of the 737-900 were produced, making it the least popular variant within the 737NG series.
Boeing later addressed these limitations with the introduction of the 737-900ER, which incorporated additional emergency exits and a redesigned rear pressure bulkhead. These modifications increased the maximum passenger capacity to 220, enhancing the aircraft’s attractiveness, particularly to budget airlines. Over 500 units of the 737-900ER were sold, far surpassing the original 737-900’s production numbers. Currently, only five airlines operate the original 737-900: Jin Air, Alaska Airlines, KLM, Korean Air, and United Airlines. Alaska Airlines, which once operated a fleet of 12, has retired all but one of its 737-900s, with the final aircraft expected to exit service imminently.
Once Alaska Airlines retires its last 737-900, United Airlines will stand alone as the sole U.S. operator of this rare aircraft variant. United currently operates 12 of these planes, making it not only the largest global operator of the 737-900 but also the world’s third-largest operator of the entire 737 family. More than half of United’s fleet comprises Boeing 737s, with 556 currently in service and an additional 286 on order. It is notable that United’s 737-900s were inherited through its merger with Continental Airlines rather than acquired through direct purchase.
United’s Expanding Narrowbody Fleet and Market Position
United’s unique status as the only U.S. operator of the 737-900 coincides with its growing prominence as the largest and sole U.S. operator of the Airbus A321neo, a model that has gained significant traction in the narrowbody market. The airline’s strategic positioning faces potential shifts amid the financial uncertainty surrounding Spirit Airlines, which currently has a fleet of grounded A321neos due to bankruptcy proceedings. Should United acquire Spirit’s A321neos, it would further consolidate its dominance with this aircraft type.
Market dynamics may also influence United’s future fleet decisions. Industry speculation suggests that United could cancel its remaining Boeing 737 MAX 10 orders in favor of expanding its A321neo fleet, particularly if Spirit’s aircraft become available. Such a strategic pivot could provoke competitive responses from other carriers, who may also seek to acquire Spirit’s assets to preserve or enhance their market shares.
As United Airlines continues to refine its narrowbody fleet strategy, its dual distinction as the largest and only U.S. operator of both the Boeing 737-900 and the Airbus A321neo underscores its evolving approach in a rapidly transforming aviation landscape.

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