Ride the sails of airline partnerships

One is based in Atlanta, the other in Seattle. One is an international carrier serving the top capitals of the world, while the other flies mostly around the West Coast. But these two very different airlines, Delta and Alaska, clearly found that opposites attract. They're the latest carriers to announce a type of partnership that's known in the industry as a "codesharing agreement."

Simply, codesharing means that one airline is allowed to place its two-letter designation, or code, on flights operated by the other. The two carriers, therefore, can sell tickets on each other's planes. In theory, frequent fliers can earn or redeem miles on either airline, as well as book a single ticket that encompasses individual flight segments on both. And members of both airlines' elite programs can get access to the other's airport lounges.

Delta and Alaska frequent fliers are already able to earn miles by flying either carrier, and have the key to each other's airport clubs. But the next phase of the partnership, including frequent flier redemption as well as codesharing, is set to roll out on January 10. Delta travelers will be able to take Alaska planes from Seattle or Anchorage to a handful of (unspecified) destinations, while Alaska fliers will be able to board Delta planes from Seattle, Anchorage, or Portland, Oregon.

Those cities only scratch the surface of the airlines' networks, of course. But the good news is that the carriers say they will be expanding their partnership in the future. However, until they do, the benefits you can enjoy from codesharing will be limited to fliers departing from those Western cities.

For example, Delta flies from Seattle only to Atlanta, Cincinnati, Salt Lake City, and New York City. The airline hasn't said which destinations it's codesharing with Alaska. But let's suppose Atlanta is one of them. The flight from Seattle to Atlanta will have both Delta and Alaska flight numbers, and the side of the plane will have a Delta logo. But fliers can choose to earn Alaska miles for that flight, instead of Delta miles. However, let's then suppose that your final destination is actually Tampa. Because Alaska doesn't yet codeshare any flights from Atlanta, you'll still have to buy a separate ticket on Delta (or another airline) from Atlanta to Tampa - even if you can earn miles on Alaska for the whole trip to Florida.

If you're riding the sails of an airline partnership, there are a couple of things to watch out for. Be sure you specify when booking which frequent flier account you want your miles credited to. And make sure to check in at the right gate: Even if Delta sold you the ticket, you need to show up at Alaska's terminal if you're flying on its aircraft. And sometimes, it won't be entirely obvious that you're not traveling on the airline your bought the ticket from; one telltale sign is a flight number of 5000 or higher.

However, despite any confusion you might experience, the ability to redeem your miles on another airline - the most important benefit of these partnerships - more than makes up for it. So if you've built up an account of Delta SkyMiles, you'll soon be able to redeem them to any of Alaska's destinations, or vice versa. And, depending on how close you live to one of these airlines' hub cities, that'll open up a whole new range of places you can fly for free.