What does "instant upgrade not available" mean?
 

Does that mean, you go on a waiting list at the airport and how does it work?

I'm looking at flights to from SJC/SFO to DCA or surrounding. I see that most of the flight from the West to the east coast doesn't have the instant upgrade. But the flight form DCA to LAX does. The ticket is almost $1050 vs $$650 between the best deal vs value fares and the Full Flex is $1300.

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Yes, it means you go on a waiting list.

As an MVP you would need to purchase a Value or Full Flex fare to qualify for an "instant upgrade." You can only upgrade at purchase if there is U space available. If you buy a qualifying fare, and no U space is available at the time, you go on the upgrade waitlist immediately, and would be upgraded if and when U space opens up, depending on where you land on the waitlist. If you buy a Best Deal fare, you would go on the waitlist at the regular 48-hour window, so it is possible to improve your upgrade chances by buying a qualifying fare, but it's complicated...other people with qualifying fares and Golds/75Ks could be ahead of you, depending on when you purchase. You have to weigh the additional cost vs. the likelihood that a qualifying fare will give you a better shot at upgrading.

The alaskaair.com page detailing Complimentary Upgrades is pretty good at explaining all this...http://www.alaskaair.com/content/mil...-upgrades.aspx