How interlining & codeshares matter to your flights

With an ever-growing number of airline partnerships, understanding how airlines work together when issuing tickets is fast becoming essential for business travellers.

Having recently explained how the difference between "marketed" and "operated" airlines affects you, this week Australian Business Traveller takes a deeper dive into what you need to know about "interlining" and "codeshares".

Interlining: the first level of working together

Simply put, interlining is the most basic level of airline cooperation.

For example, if you're travelling from Sydney to Hong Kong and then connecting through to Mumbai, Qantas will make a single reservation and sell you a single ticket covering its own Qantas flight QF127 (Sydney to Hong Kong) plus Cathay's CX685 (Hong Kong to Mumbai).

You can usually collect both your boarding passes when you check in at Sydney, and you'll be able to connect from one flight to the next without going through out through security and checking in again.

Nor will you have to pick up your bags in Hong Kong to re-check them onto the CX flight.

And if your incoming flight arrives late, it's the task of the airline you bought the ticket from to sort out a new connection, instead of that job landing on your tired shoulders.

So interlining makes things a lot easier, and it can be vitally important when flights are delayed or things go wrong.

Interline agreements mean that a missed connection isn't always your problem

Many low-cost carriers say they're "point to point only" airlines and you book connections on them at your own risk: if they're late and you miss your onwards flight, you'll be socked with change fees or the requirement to buy an entirely new ticket on that connecting flight.

It's the same even on full-service airlines. If you buy two separate tickets for your connecting flight (which can in some cases be cheaper), the airline is under no obligation to sort you out with an onward flight if you miss the second leg of your journey.

However, one caveat in the event of a flight mishap: you need to approach the airline you bought the ticket from rather than the airline whose desk you're standing next to. In the example we gave above, this would be Qantas rather than Cathay Pacific.

It's the old "talk to the travel agent who booked this ticket" problem from years ago (before we really booked tickets from the airlines direct) except that the travel agent in this case is the other airline.

While things will usually get sorted out, it can be frustrating and slow.

Codeshares: interlining plus a bit more

Airlines codeshare with one another by putting their own airline code on the other airline's flights. Qantas coined the term back in 1989 with American Airlines, and it's really taken off in the years since as airlines look to increase their connecting traffic.

For example, Virgin Australia flight VA8004 from Sydney to Auckland is actually an Air New Zealand plane tagged as flight NZ104. And that same plane is also Air Canada 6104, Air China CA5143 and Singapore Airlines SQ6838.

Codeshares see the same flights carrying several different flight numbers

Since codeshares mean the airlines are working more closely together, connections are a bit easier — luggage and flight transfers are usually better coordinated by the carriers — and the "who's responsible when things go wrong" is usually handled better than when airlines are only interlining.

You get all the benefits of interlining, and often you'll enjoy extras such as lounge access, more frequent flyer points and status credits.

But you're unlikely to get exactly the same benefits as when you fly on your own airline — the old "marketed and operated" problem rearing its head. That's why many frequent flyers keep a watchful eye out for codeshares and try to fly their own airline as much as possible instead.

For the very latest business travel news, follow @AusBT on Twitter.

John Walton

Aviation journalist and travel columnist John took his first long-haul flight when he was eight weeks old and hasn't looked back since. Well, except when facing rearwards in business class.