When are alliance frequent flier accounts mutually supported?

Question

Say an airline alliance has airlines A, B, C, and D.

I have only registered for a frequent flier account for A. I am booking on C. When I book on Expedia, I have a dropdown option for basically every frequent flier program in the world, not necessarily what will be supported (certain things that obviously wouldn't be supported, like another airline not in the same alliance).

I select the frequent flier program for A, and enter my number for A in the text box next to it, and finish booking the flight on C.

How often / in what cases does this work? I tried it recently, but I just checked and the miles weren't credited. I didn't take the flight yet though, so maybe they will be credited after I fly.

If it is really case-by-case, it's hard to see how this would be a viable strategy since there are too many possible combinations to remember.

But if it DOES work then it is probably the only way to accrue decent frequent flier points if you 1) only fly 2-4 times a year, and 2) always take the cheapest flight regardless of airline. The alternative (signing up individually for every airline you use) won't work since you'll have too few flights, they will expire, etc.

Answer 1

You won't accrue miles before you actually fly.

Expedia just supplies a giant list of options so you can enter your account number. They'll pass that along to the airline. The airline's computer systems will decide whether you actually get miles (and how many) after you fly, based on the individual policies of each frequent flyer program. Every program will detail somewhere the specific ways to earn miles for that program, including their partner airlines (both those partners from an alliance and any non-alliance partners).

For example, United's MileagePlus lists the ways to earn miles and its partner airlines, Star Alliance and others. Clicking each partner will take you to a page showing the mileage accrual rules for that airline based on fare, distance, class of service, etc... If you enter your MileagePlus number and fly an airline that isn't listed, such as Delta, you're not going to earn any miles. If the airline is a partner, you'll get the miles credited to your account (in theory) after you fly.

I say in theory because the process occasionally breaks down and the miles never make it into your account, especially when multiple airlines are involved. Every program will have some mechanism to request credit in these situations. It's a good idea to save your boarding passes until after the miles are credited, as you may need that information to make such a request.

As you've noticed, if you fly infrequently, have no loyalty to any particular airline, fly the cheapest fares in economy, and don't use an airline credit card, you're unlikely to accrue a whole lot of frequent flyer miles (though you can build up a balance slowly, being careful to ensure you don't let any expire). That's not a travel pattern that airlines have a particular interest in rewarding.