An airline sells something you can't hold in your hand: a flight from one city to another. So its supply chain looks different from a phone maker's. To provide a service, a business acquires the employees, resources, and delivery systems it needs. For an airline like Southwest, that means hiring and training pilots and flight attendants (the employees), buying or leasing planes and jet fuel (the resources), and running a booking system plus airport gates (the delivery systems that get the service to customers). As of its fiscal year 2023 fleet, Southwest flew only one type of plane, the Boeing 737 (its entire 817-aircraft fleet)^[1]. Sticking to a single model keeps training and repairs simpler, because every crew and mechanic works with the same aircraft. The service is delivered in person. You show up, board, and the airline flies you where you're going.