I recently had the opportunity to spend a week of vacation at the Hale Koa Hotel in Hawaii, one of the Armed Forces Recreation Center hotels run by the military. While there, I talked with fellow retirees who were also on vacation - many of whom had traveled by space-available military flights. As one retiree said, "It's not always the most convenient way to travel, but the price is right" - especially if a first-class hotel is on the other end.

I have traveled on space-A flights a number of times over the years and have found that if you have the time and flexibility, it is well worth the investment. Not only does traveling space-A offer incredible discounts for retirees, but it seems more efficient today than traveling by commercial airliner, where your knees are in your chest and everyone is trying to cram a 3-foot-long piece of luggage into a 2-foot-long overhead space.

For those who have never flown space-A, here is some basic information on how it works and eligibility rules.Eligible passengers can fill unused seats on aircraft owned or controlled by the Defense Department once all the space-required (duty) passengers have been accommodated.In stark contrast to civilian air travel, there is no centralized process for booking seats on space-A flights.

It is a fragmented system that requires extra diligence on the part of space-A travelers, along with patience and flexibility.You are placed in one of six categories based on a combination of two criteria: your status (for example, active-duty member, retiree, Department of Defense Dependents Schools teacher), and your situation (emergency leave, ordinary leave).

The categories that determine your order of selection for space-A flights, from highest to lowest priority, are:

Category 1: emergency leave.
Category 2: environmental morale leave (EML).
Category 3: ordinary leave.
Category 4: unaccompanied dependents on EML.
Category5: permissive temporary duty and students.
Category 6: retirees (retired military members who are issued DD Form 2 and are eligible to receive retired or retainer pay).

A retiree's family members (with a valid ID card) also are eligible when accompanied by a sponsor.Space-A passengers must register by fax or e-mail at all passenger terminals where they want to catch a flight. Because space-A passengers travel only after all duty cargo and duty passengers have been accommodated, there is no guarantee that a flight will have enough seats for every potential passenger.

When you register, you are assigned your category of travel. You will be selected based on your category and the date and time of your registration. This date and time of sign-up determines your selection on all flights to your final destination; you get a new date and time when you register for your return travel.You have the option to stand by for any flight you think you have a reasonable opportunity on which to travel.

Travelers remain on the register for 60 days or the duration of their leave orders or authorization, whichever happens first.Space-A travel has undergone a great deal of change in the past few years. For the latest details, visit Air Force Air Mobility Command's Web site at http://public.amc.af.mil/Library/SPACEA/24_203.htm.

A list of passenger terminals and phone numbers is there.For retirees, especially older retirees who have no fixed schedule and have the flexibility to deal with the sometimes unpredictable nature of space-A flight, this can be a great way to travel - and for a fraction of the cost of commercial air. Some terminals must collect a head tax or a federal inspection fee from space-A passengers on commercial contract missions, but it's a nominal fee.

Meals also can be purchased at a nominal amount out of most air terminals.Military exchange bookstores sell space-A guidebooks that more fully explain the ins and outs of how the program works, with helpful advice for how to get the most out of it.

Alex Keenan, a retired command master chief, served 28 years in the Coast Guard. E-mail him questions, comments and suggestions at retired@atpco.com.