Airlines, Alliances & Codeshare

Types of airlines

Airlines broadly fall into a few business models. Full-service network carriers offer multiple cabin classes, connect passengers through hubs, and typically belong to a global alliance. Low-cost carriers (LCCs) focus on point-to-point routes, simpler fare structures, and lower operating costs. Regional airlines operate smaller aircraft, often flying on behalf of a larger carrier under that carrier's brand. These categories increasingly blend — many full-service carriers now have low-cost subsidiaries, and some LCCs have started adding features like assigned seating or connecting itineraries that used to be associated with full-service flying. A full-service network carrier, for example, might operate long-haul widebody flights to distant hub cities, feed short-haul narrowbody or regional flights into those hubs, and still sell a single connecting itinerary spanning several of its own subsidiaries.

Mainline and regional branding

Many of the smaller aircraft flying under a big airline's name aren't actually owned or crewed by that airline at all. A regional airline often operates flights branded and sold as part of a major carrier's regional network — using that carrier's livery, flight numbers, and check-in counters — while running its own separate operation with its own aircraft, pilots, and cabin crew under a capacity purchase agreement. The regional carrier is paid to fly the route; the mainline airline sets the schedule, keeps the ticket revenue, and takes the branding risk. Passengers usually can't tell the difference at the gate, but the two companies can have entirely different pay scales, aircraft types, and even different operating cultures behind the same paint job.

The three global alliances

Most of the world's largest airlines belong to one of three alliances: Star Alliance (founded in 1997), oneworld (1999), and SkyTeam (2000). Alliance membership lets airlines coordinate schedules, share lounges, align frequent flyer benefits, and sell connecting itineraries across each other's networks — without merging as companies. Not every major airline joins an alliance, though; some large carriers choose to stay independent and instead build a web of individual codeshare and interline deals with whichever partners suit their network, rather than committing to one alliance's full membership requirements.

Codeshare flights

A codeshare is when an airline sells tickets, under its own flight number, for a flight that's actually operated by a different airline. If you book "Airline A flight 123" but the aircraft, crew, and operating certificate all belong to "Airline B," that's a codeshare — Airline B is the operating carrier and Airline A is the marketing carrier. It lets airlines offer a wider network on paper than they physically fly, while passengers still deal with one airline's booking and one journey. Regulators generally require the operating carrier to be disclosed at the time of booking, since it's Airline B's aircraft, crew, and safety record that actually apply to the flight, whatever flight number appears on the ticket.

Interline agreements

Even outside formal alliances, airlines often have interline agreements — bilateral deals that let them check baggage through and rebook passengers onto each other's flights, especially useful when a connection is missed or a route isn't covered by either airline alone. For instance, if a passenger's connecting flight is delayed and they'd otherwise miss a second leg operated by a completely different airline, an interline agreement can let that second airline rebook them onto a later flight and make sure checked bags follow along, without the passenger having to reclaim and recheck anything in between.

Joint ventures and antitrust immunity

Some alliance partners go a step further than ordinary codesharing and form a joint venture on specific routes, most commonly across the Atlantic or Pacific. In a deep joint venture, the participating airlines coordinate schedules, pricing, and revenue on those routes almost as if they were one airline, sharing profits and losses on the combined operation rather than just splitting individual tickets. Because this level of coordination would normally raise competition concerns, regulators sometimes grant antitrust immunity, a specific legal approval allowing the airlines to cooperate this closely on the approved routes without it counting as illegal price-fixing. Immunity is usually route-specific and can be reviewed or withdrawn, so a joint venture doesn't automatically extend across an airline's entire network.

Wet lease and dry lease

Airlines sometimes borrow capacity from each other. A wet lease (ACMI — Aircraft, Crew, Maintenance, Insurance) means one airline supplies a fully crewed aircraft to operate flights for another, often to cover a seasonal spike or a fleet gap. A dry lease is just the aircraft itself, with the receiving airline supplying its own crew — more like a long-term equipment rental. A damp lease sits in between: the lessor provides the aircraft and some, but not all, of the crew — typically just the flight deck — while the receiving airline supplies its own cabin crew. ACMI contracts often run for weeks or months rather than years, making them a flexible way to add capacity quickly without the long-term commitment of buying or leasing an aircraft outright.