Marriage logic is a mechanism airlines use to manage their inventory and revenue. Just like regular marriage, it can sometimes be complicated, frustrating and counter-productive.
As a concept, using marriage logic to minimise the costs involved in flying planes around at low capacity and to maximise revenue makes perfect sense. Having said that, its application is often less than perfect.
What is marriage logic?
When flights are searched from A to B and then separately from B to C, the availability can be drastically different to the availability when the flights are searched from A to C via B. 
When you search and hold flights from A to C via B, the two sectors (A to B and B to C) are “married” and it is not then possible to cancel either sector without cancelling both. If the flight from A to B is searched first and held in, this will affect the availability of the flight from B to C if you then search for it in the same reservation where the first flight is held. If you hold the flight from A to B and then hold in the flight from B to C in the same reservation, the two flights will automatically marry as well.
Marriage logic affects availability all too frequently with award booking classes and understanding marriage logic and how different airlines apply it can actually help you get better results when trying to book an award ticket over the phone.
Why do airlines marry segments?
The reason that airlines use marriage logic is to strategically price their yield to maximise revenue and avoid flying planes with too light a load. As an example to illustrate how this works, imagine an airline has a flight from Dubai to London that only has 10 seats left available for sale in economy class. They have another flight departing Dubai for Paris at roughly the same time and have the entire cabin empty. They also have a flight from Sydney to Dubai that can connect to either of the flights to Europe that is about half full in economy. When you take into consideration the insane amount of money it costs to operate a long haul flight (fuel, staff, airport costs, amortisation of the aircraft etc etc etc…), it’s fair enough that they need to be quite smart about how they handle their limited inventory.
So, if someone searches Sydney to Dubai only, they might be given availability in half of the economy fare buckets, so not the cheapest fares but not pushed right up to full economy either. If they search from Sydney to London, all of a sudden this availability disappears and the whole way, on both flights, they are only now given full fare economy and the lower booking classes that were available on just the Sydney to Dubai flight are gone. Then they search Sydney to Paris and all of a sudden everything is available!! Even the cheapest tactical fare buckets are available on both legs!
How can this push up the price of flights?
When a flight is close to capacity, that’s when the airlines can actually start making a profit on the flight. They’ve covered their costs for the service and if someone wants to book onto it they’re going to charge accordingly because that’s their opportunity to do so. If a passenger wants to save money then they can travel on an alternative day or time on a flight where the airline is still looking to cover their costs.
When a flight is very empty, the airline will make exceptions to the availability on connecting flights to funnel passengers onto it and get closer to covering the costs of flying that plane.
It makes perfect sense. Except sometimes it doesn’t.
Qatar Airways, as much as I love them, which is a lot, often have mind bendingly illogical marriage logic. As an example, if I search right now for a flight from Sydney to Doha on the 10th of July, I can get any booking class in economy including O which is their lowest tactical fare bucket. If I search the next connecting flight from there to Mahe in the Seychelles, departing early in the morning on the 12th of July, the availability is the same. Wide open in every fare bucket. If however, I search from Sydney to Mahe both flights are mysteriously blocked out and the only availability is a single first/business class seat and not a single seat in economy for sale on either flight.
When the airline’s inventory management system is blocking every single seat, I just can’t comprehend how that is helping their cause. If someone is looking at travelling from Sydney to Seychelles, Qatar are just taking themselves out of the game completely. That can’t possibly be clever business, just refusing to sell seats to customers.
How to (sometimes) get around it
Now there are some less than legitimate ways to get around an airline’s marriage logic / yield management. This of course isn’t allowed and is called “OD abuse”, OD meaning origin and destination. When a travel agent “breaks” marriages, the airline sends them an ADM, which is essentially a fine. These can be pretty hefty depending on the airline and can sometimes consist of a nominal fee plus the fare difference between what was ticketed and the full fare for that cabin as they are generally unable to retroactively assess what the availability should have been like on the day the ticket was issued. As you can imagine, these fare differences can be huge.
Having said that, there are sometimes ways to get around the yield management systems blocking out seats without breaking marriages. While holding flights out of order is technically OD abuse, it’s generally not picked up by the airline (with some exceptions) and doesn’t usually raise any flags. This is a way in which it’s sometimes possible to get award seats when they’re not there on first glance.
To illustrate what I mean by holding flights out of order, I’ll explain an example where I was able to get some Cathay Pacific business class seats with Alaska Airlines miles that didn’t appear available at first.
When I was searching for availability, I was looking for Sydney to New York and finding no available seats on the British Airways Executive Club website as Cathay Pacific availability doesn’t come up on the Alaska Air site. So then I tried searching Sydney to Hong Kong and Hong Kong to New York separately and there were seats available on both legs. Knowing that Cathay’s yield management can sometimes be massaged by holding the flights out of order, I picked up the phone and called Alaska Air. First I asked the agent to search the whole way and he confirmed there was nothing available. Then I asked him to search Hong Kong to New York first, hold that in and then search Sydney to Hong Kong. He didn’t sound convinced but sure enough, was able to get award availability for me. Result!
Another way to sometimes get around seats being blocked by yield management systems by being strategic in the order of flights being held is when there are multiple airlines being used in a reservation. As an example, Qantas’ yield management tends to block out the lower fare buckets when there are other carriers already being held in the reservation. So an obvious way around this is to hold in the Qantas seats first and then hold in the other carriers flights. So if you were looking at booking an award that had flights with both Qantas and Japan Airlines with Aadvantage miles, for example, and you’d already confirmed online that all flights individually had availability but when searched together the availability vanishes, you could call up and ask the agent to search and hold the Qantas seats first and then add in the JAL flights.
Not all airlines use marriage logic
Not every airline uses this sort of yield management but it’s becoming more and more common. Qantas only started using it in the last few years, Air New Zealand are currently rolling out marriage logic across their network and you can bet many more will follow.
Much the same as is the case with regular marriages, each airline’s system has its own quirks and just when you think you’ve figured out how to get it work for you, the goalposts are moved. That’s why marriage (logic) can be so frustrating at times for travel agents and anyone booking flights.
PS. Only joking about regular marriage, it’s super great! Hi Alessandra! xx
I thought you were writing about the “other” marriage one encounters in life! Interesting post. The algorithm writers will have a feast.