Interline agreement

The baseline pact between two airlines to accept each other’s tickets and transfer each other’s bags — well short of a codeshare or joint venture, but the plumbing that lets one itinerary span carriers. Interline matters most when things go wrong: with an agreement in place, a misconnection can be rebooked onto the partner; without one, each carrier shrugs toward the other. Low-cost carriers mostly do not interline, which is a hidden risk of bolting one onto a premium itinerary.