Codeshare Flight
A flight operated by one airline but sold under two or more different flight numbers — you may check in with an airline that doesn't own the plane.
What is a codeshare?
A codeshare agreement allows two or more airlines to sell seats on the same physical flight under their own flight numbers. The plane is operated by one airline (the "operating carrier") but marketed and ticketed by the other (the "marketing carrier"). A passenger flying BA2156 from London to New York might actually board an American Airlines aircraft, with American crew, on an American-operated route.
Codeshares are extremely common. Most international flights involve at least one codeshare arrangement. They exist because airlines want to offer connections to destinations they don't serve directly, without the cost of operating the route themselves.
Why does it matter to passengers?
The operating carrier determines the onboard experience: the aircraft type, the seat configuration, the meal quality, and the cabin crew. The marketing carrier handles the ticket, the check-in process, and often the frequent flyer miles accrual. A ticket sold as a premium airline can sometimes mean a budget airline's product in practice — and vice versa.
When searching for flights, always check which airline actually operates the flight (shown as "operated by..." in the booking flow). If onboard quality matters to you, look up the operating carrier's product for that specific route rather than relying on the branding of the airline you booked with.
Codeshares vs interlines vs alliances
A codeshare is deeper than an interline agreement but narrower than a full alliance. An interline agreement allows two airlines to handle each other's baggage on separate tickets. A codeshare goes further: it puts both airlines' flight codes on the same flight. An alliance (Star Alliance, Oneworld, SkyTeam) creates a network of codeshare and interline relationships across dozens of airlines simultaneously.
For travellers seeking seamless connections, a booking with codeshare or interline coverage means your checked luggage travels with you even when you change airlines, and if the first flight delays you, the second airline is responsible for rebooking you.