Dave Barry once wrote that there is a federal law that no two people on a plane can pay the same price for their seat. Airlines use complex systems to manage ticket prices, constantly changing them based on expected demand and competition, and with over a dozen fare classes with different rules.

When it comes to the rules, a usual principle is that only the more expensive tickets give you the flexibility to change your plans. For any reasonable price, you will have change and cancellation fees, and for the lowest cost tickets, changes are next to impossible. This is compounded by the fact that changes usually require paying the difference to the current price, but the current price in the few days before a flight is the very expensive flexible price. Missing a flight or deciding to move a fight a day can be hugely expensive.

The flexible tickets are ridiculously expensive as well, often 2x or even 3x the inflexible cost. In general, unless you change your plans a lot, you are still better off buying the cheap inflexible tickets and then eating the high cost on the relatively rare times you make changes. (Many airlines do offer cheap "same day" changes, particularly to status flyers.)

Flexible tickets can command this price because they are of greatest use to business passengers. We fly more on short notice, and need to make sudden changes, while people on vacation generally do have a fixed schedule. Airlines know business customers will pay more, and so they search for things that only business passengers want, and charge heavily for them.

Sell me a ticket where I have to be flexible

For leisure travel, here's an alternative. Sell me a ticket that allows reasonable and low-cost changes when seats are available. Make it not a big deal to let me leave when I want to. To make this ticket cheap, but a big burden on me -- the airline can also delay my flight.

What this would mean is that up to some amount of time, like 24 hours before the flight, the airline can email me and say, "Sorry, that flight is selling out, we've moving you to another flight." The other flight would be within a time window -- the longer the window, the cheaper the ticket. 24 to 48 hours would usually be enough.

The typical business passenger is not going to tolerate this. In business, time is money and losing a day just isn't an option.

Some leisure passengers would not tolerate it either. If you have other bookings that are hard to change, like sold-out hotels, or a cruise, you don't want to miss them. (Though in the world of flight cancellations you have to prepare for this sometimes.) But many hotels and other things are pretty flexible.

Most could handle such a rule going home, unless they are going home and must get to work the next day. For retired people, and the many people who work flexible schedules (consultants, writers and many other self-employed) it is not a big issue to get home a day or two late. And for many of these people it's also not a big issue to arrive at the destination a day late, and certainly not a few hours late. In addition, many people taking an extended trip to multiple cities would be perfectly fine with the idea that they might spend an extra day in Rome and a day less in London, or vice versa. (On shorter trips with several flights a day, the delay might well be only a few hours.)

You could also offer the airline the power to make you leave earlier, but they would have to give you more notice on most legs.

This is great for the airline. They get the power to move people off full planes to replace them with high revenue customers at no cost, and put them on planes that are less full, where the seats are almost free. (If both planes are full, they would not move you.) Today they do this by asking for volunteers and paying them with vouchers, or on some occasions doing a forced bumping.

This is like standby, in a way, but less uncertain than that. A bit more like the way employees fly free on their off-hours.

There is one class of business passenger who might tolerate this, namely those making a visit to a branch office. They might be able to continue work for another day at the branch rather than go home if they don't have meetings scheduled. I don't think there would be a lot of this, unless you could also do it for business class tickets.

As part of the deal, the airline would also offer you a guaranteed low rate on an airport hotel for your extra day. They already have negotiated rates and spaces. With advance notice, though, you will probably be able to stay at your own hotel unless you travel at a sold-out time. These fares might make more sense in shoulder seasons, where hotel changes are easy.

As a passenger

As a reminder, you do all this to save money on a flexible ticket. You get a ticket where you can leave whenever you want without a large change fee. For a certain class of voyager (the retired in particular) this is the sort of ticket they want. Of course, seats have to be available, you can't switch to a sold-out flight, and seat selection may be limited if you do things on short notice. But it need not always be on short notice.

The notice from the airline could even be long, too. Their computers are estimating the load all the time, and they might send you a request to move even a week or month in advance. For a higher cost, you might lengthen the window so you need a week's notice if you are going to be moved (and they might then move you forward or backward.)