This is a nested ticket and is technically against the contract of carriage with the airline, as you're trying to avoid paying their fees. Very hard to get caught, but if so they would try to come after you.
I don't see how it would be hard to catch. They have uniquely identifying information on each passenger, so just arrange the flights sequentially, and if one matches up, then compare which is 1st leg or 2nd leg and flag it. They can probably even ban you from the airline, and then what? There are quite a few monopolized airports and routes in the US, s you can be majorly inconvenienced by not being able to fly one an airline.
The question is, how badly do they want to catch it?
If it's something only a small fraction of the customers actually bother to do, it doesn't dig into their profits too much.
It effectively acts as another form of market segementation. There is a mostly fixed cost for flying an airplane; the marginal cost per passenger is relatively low. So ideally, you would have a paying passenger in every seat. Some passengers are more price sensitive than others, so you want to have the less price-sensitive passengers pay as much as possible, while still providing ways for the more price sensitive passengers to get fill up seats that are still available after that.
People who are willing to go to the trouble of doing this will happen, but you're still making money off of filling seats with paying customers, they're just acting as slightly more price sensitive passengers.
The airlines fluctuate rates for just this reason; they want people to be able to buy tickets at different prices, so price sensitive passengers can go to a little more trouble to book earlier or take bigger risks by flying standby or waiting for the price to go down if it's not appropriate, while less price sensitive passengers will just buy the ticket whenever convenient.
If this were being seriously abused a lot of the time, or there were automated systems which booked trips like this for you, I could see the airlines doing something about it, but if it's just a few people going out of their way to get a slightly better price, it's probably just considered to be part of the whole ticket pricing game.
> If this were being seriously abused a lot of the time, or there were automated systems which booked trips like this for you, I could see the airlines doing something about it, but if it's just a few people going out of their way to get a slightly better price, it's probably just considered to be part of the whole ticket pricing game.
This is pretty much how it's gone so far - sites that have offered anything even resembling an automated service to do bookings like this (and similar other tricks) have been aggressively fought by the airlines legally.[0]
There are also a very small handful of stories per year about some frequent flier getting caught abusing these sorts of fares habitually and getting a trip canceled and/or banned from the airline.
As far as I know my airline flags all sorts of trips like this - but doesn't do anything about it unless it becomes obviously gamed. For example I fly between two cities frequently for week long+ periods, but may need to go home for a weekend during a 2 week stay now and then. I know my airline flags that, but haven't had a problem since it only happens a few times a year out of dozens of total trips.
Pardon my ignorance, but how does this avoid fees? I can see this being an issue with international flights with visas and whatnot but don't you pay the same fixed rate per flight in the US?
> don't you pay the same fixed rate per flight in the US?
In a word, no.
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Flights in the US are dynamically priced. Each airline decides how much they want to charge per particular flight for a particular person at a particular time (meaning, when you purchase the ticket). Prices fluctuate constantly. If you look up a flight from City A to City B today (and said flight departs within a reasonable amount of time; say, a month), it's fairly likely to have a different price tomorrow. Prices can also vary based upon how you book the ticket (i.e. travel agent, different travel websites, by phone, etc.).
It's very much possible, and generally expected, that you and the person you're sitting next to paid different amounts for what amounts to the same ticket.
