United Airlines has announced that Mileage Plus miles will begin expiring after 18 months of inactivity. This is down from 36 months, and matches similar moves by US Airways and Delta (24 months) recently. You can read United’s press release by clicking here.

Personally, I am indifferent to the change, and lean towards it being a good thing. It is a frequent flyer program afterall, and if you aren’t flying at least once every 18 months, one could wonder just how frequently you are flying, couldn’t they?! You don’t even need to fly. Any activity in the account will preserve your miles, so use your Mileage Plus Visa, buy some flowers, dine out at certain restaurants or buy groceries. Those are just a few of the ways you can earn miles.

I suspect that this will be the beginning of a trend. I haven’t seen any figures lately, but I believe the number of unused miles sitting in frequent flyer accounts is in the trillions. This represents an enormous liability for airlines. These programs have evolved over time to become revenue generating machines for the airlines. They make money by selling miles to all those various entities that offer them as an incentive such as credit card companies. I’ll have more to say about frequent flyer programs in the near future, as I believe we are seeing the beginning of a permanent change in the way these programs are operated.