You would think that when you bought a ticket for a flight, you'd get the itinerary you paid for. That isn't always the case, especially if you book far in advance.

Airlines change schedules as time goes by, and that can mean that you end up with something different than what you wanted when you bought your ticket. This is particularly problematic during mergers, when airlines make a ton of changes as they work to combine two airlines into one. With two big mergers happening right now (United/Continental and Southwest/AirTran), there's a good chance you've seen this happening when you fly.

So what can you do about it? You actually have options here, but the options depend upon what actually changed.

Sometimes, it's just a matter of a change in the flight number. When that happens, the flight times stay the same, and it's really not an issue. Other times, it's just small flight time changes. You'll see flights moved by a couple minutes here or there. If it's a tiny change, then there really isn't an issue -- unless it busts the minimum connection time.

There are published minimum connection times at every airport between every airline. You won't be sold a connection with less than that amount of time, because it's not reasonable to think you could make the flight. But if flight times change, you might be unwittingly moved into a connection that doesn't meet the requirement.

Unfortunately, these minimum connecting times aren't readily accessible to the general public, but you can always call the airline to ask. Another option is to go to the airline website, do a search as if you're buying a new ticket, and see whether your new connecting time still shows up as an option. If it does, it's still a legal connection.

But what can you do if it's not? Or what if an airline makes a major flight time change? I've dealt with a few of these lately with some of our clients, and the results have varied.

In one example, someone was scheduled to fly in the morning from Miami to San Francisco via Houston a couple months from now. United decided that flight would no longer operate, so the only other option at remotely the same time was to send this person through Washington and then on to San Francisco. This added hours to the travel time and was a lot more flying than expected.

In cases like these, United and other airlines will allow you to change to another reasonable connecting option without any additional charge.

And if there isn't a reasonable option? That's where it gets sticky. Each airline decides whether the change is large enough to warrant allowing a refund. If not, then you'll probably have to pay the change fee to use the value of that ticket for a future trip or find a way to make the airline schedule work.

For more severe changes, you'll be able to get a full refund and buy a new ticket on another airline. Although it would be nice for airlines to put you on another carrier at no charge, they will almost never do it.

If you find yourself looking for that refund, I'd suggest checking for better options on other airlines first. If you find one, go ahead and get a refund for the first ticket and buy the new one. Sometimes you'll find that this is a good thing. Maybe the price has gone down on a new ticket, so you actually save money thanks to the airline's change.

In general, once you get within a couple of months of your flight, schedule changes become rare. But it's always a good idea to make sure that the airlines have your phone number and e-mail address just in case.