People with stockpiles of Continental Airlines frequent flier miles who haven’t flown in a while may want to pay attention to this. When that airline finally weds its frequent flier program to that of United Airlines in 2012, the clock could be ticking before those miles disappear.

This morning, the combined airlines announced some details of the merged airline miles programs. As part of the change, miles will expire in accounts that go inactive for 18 months. Continental OnePass miles currently have no set expiration date.

“We want people to engage in the program and we want them to do that more often than every 18 months,” an airline exec said.

But you don’t have to fly to keep your account active. You can use a United branded credit card or make purchase from some of the airline’s partners.

On the plus side, the combined program will allow all members to apply to the Global Entry program, which allows travelers who pass background checks to skip long lines at the airport’s international customs checkpoint. Of course, it costs $100 to apply, though that charge is waived for fliers in the top three MileagePlus tiers.

United, Continental detail merged frequent-flier plan [Chron.com]

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