Executive Travel : Frequent Fliers Need to Frequently Review Rules

Business travelers who thought they understood the pros and cons of each mileage program need to recalculate over the next year as most of the major airlines make their plans more restrictive. The key change is raising from 20,000 to 25,000 the number of miles needed for a ticket within the continental United States and Canada. Some have also increased their requirements for travel to Mexico or the Caribbean and to Europe.

But there are some bright spots.

* TWA intends to hold the line at 20,000 for a domestic ticket, a spokeswoman said. But the airline did raise the mileage level for a second ticket to Europe to 50,000 miles, from 40,000 previously, and boosted the requirement for travel to the Middle East to 50,000 miles year-round, from 35,000 miles previously for winter flights.

* Southwest Airlines, which bases its program on trips rather than on miles, recently cut its requirement to eight round trips (instead of 10) to qualify for a free round trip. But the airline requires that the eight round trips be made within 12 consecutive months.

* Delta decreased its requirement for a domestic coach ticket from 30,000 to 25,000 miles. But the airline also imposed a new expiration requirement, though it is less severe than other airlines’ because fliers can keep mileage by taking a trip on Delta every few years.

While miles earned to date and until the change takes effect on May 1, 1995, will be valid as long as Delta runs a frequent-flier program, miles earned after that date will be good only for 36 months from the date of the traveler’s most recent trip.

* Miles themselves are becoming increasingly exchangeable. American Express Travel Related Services Co., for example, recently announced that five major hotel chains have entered into its program--called Membership Miles--making it possible to turn frequent-flier miles into free hotel stays.