Space-A, or Space Available, military flights are available to active and retired service personnel, some Department of Defense employees and eligible family members. Seats are also available to those in the military reserve and the National Guard.
Passengers must register at the military passenger terminal using military ID and leave papers if applicable. A few terminals allow signing up via email or fax. After registration, the passenger is assigned a category, which determines how the seats are assigned.
Active duty personnel and their families on emergency leave are assigned Category I. Category II is assigned to service personnel and family members on EML, or Environmental Morale Leave, and those stationed outside the United States.
Those traveling on ordinary leave are assigned Category III, while unaccompanied family members on EML are assigned Category IV. Category V goes to certain student travelers, while Category VI goes to retiree and their families and certain National Guard and reserve members. Category VI is assigned last.
Due to security concerns, flights are not published online. Information is obtained at a military passenger terminal. Space-A flights are usually free. Exceptions include flights contracted with certain air carriers, which might charge a minimal fee. International travelers may need to pay departure taxes.