What Interline means
Interlining lets a passenger buy one journey that uses several airlines, even if the carriers have no deeper partnership. Each flight keeps the operating airline's own flight number. This is the key difference from a codeshare, where one airline puts its code on another airline's flight.
The ground rules are set out in IATA's Multilateral Interline Traffic Agreements (MITA), which describe how airlines collect money and issue documents for carriage on each other's services, for both passengers and cargo. Because tickets are now electronic, carriers also need e-ticketing interline arrangements. IATA's BIETA data captures bilateral ticketing agreements made outside the MITA framework, covering 4,626 passenger and cargo ticketing agreements (as of 2026).
Money moves after travel. The ticketing (validating) airline holds the passenger's payment, then bills and pays partner airlines for the segments they flew. Many airlines settle these balances through the IATA Clearing House, which reports more than 560 participants, including 330 airlines (as of 2026).
IATA is also developing interlining with offers and orders as part of its modern airline retailing programme, so that partner content can be combined in ONE Order environments. For agencies, interline agreements decide which multi-carrier itineraries can legally be issued on one ticket.
How Interline works
An interline journey depends on agreements made long before the booking and on settlement after the trip.
- Airlines sign agreementsCarriers join MITA or sign bilateral interline and e-ticketing agreements that allow them to ticket each other's flights.
- The itinerary is pricedA through fare or combination of fares is built for the whole journey, following each carrier's fare rules.
- One ticket is issuedThe validating carrier issues a single e-ticket with a coupon for each flight, including the partner's segments.
- Partners carry the passengerEach operating airline accepts the coupon for its flight, and bags are typically checked through where agreements allow.
- Revenue is settledThe validating airline prorates the fare and settles with partners, often through the IATA Clearing House.
Interline in practice
Illustrative journey: a traveller flies Dhaka to Dubai on Airline A, then Dubai to Frankfurt on Airline B. The two carriers have an interline e-ticketing agreement, so the travel agency issues one ticket validated on Airline A. The ticket shows Airline A's flight number for the first segment and Airline B's own flight number for the second.
Airline A collects the full fare through the agency's settlement plan, such as BSP. After travel, Airline B bills Airline A for its share of the fare for the Dubai to Frankfurt flight, and the balance is settled through the clearing house.
Not interlining (illustrative): if the same traveller buys two separate tickets, one from each airline, there is no interline agreement covering the journey. Each ticket is a separate contract, and the second airline has no obligation linked to the first flight.
Who uses it
Advantages and limitations
Advantages
- Airlines can offer many more destinations by selling partners' flights alongside their own.
- Travellers get one ticket, one booking and, typically, baggage checked through to the final destination.
- Multilateral frameworks such as MITA reduce the number of separate contracts each airline must negotiate.
Limitations
- Not all airlines interline, and many low-cost carriers sell only point-to-point journeys.
- Prorating and settling revenue between airlines adds accounting work and can lead to disputes.
- Legacy interline processes rely on tickets and coupons, which fit poorly with order-based retailing.
Frequently asked questions about Interline
What is the difference between interline and codeshare?
On an interline ticket, each flight is sold under the operating airline's own flight number, and the airlines simply agree to ticket and accept each other's segments. In a codeshare, one airline sells a seat under its own flight number on a flight another airline operates. Codeshare partners normally also interline, but interlining alone does not involve shared flight numbers.
What is a validating carrier on an interline ticket?
The validating carrier, sometimes called the plating carrier, is the airline whose ticket stock is used and which receives the passenger's payment. It must have interline agreements with every other airline on the ticket. It later pays partner carriers their share of the fare for the flights they operated.
What is MITA in airline ticketing?
MITA stands for Multilateral Interline Traffic Agreements, an IATA framework that sets out the basic rules airlines follow when collecting money and issuing documents for travel on each other's services. IATA publishes the agreements and lists of participating carriers for both passenger and cargo traffic.
Do low-cost airlines interline?
Many low-cost carriers have traditionally avoided interlining because their model is built on simple, point-to-point sales through their own websites. Practice varies, though, and some low-cost and hybrid airlines do sign interline agreements with selected partners. Agents should check each carrier's current agreements rather than assume either way.
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