Military members use AMC Form 140, Space-Available Travel Request, to travel on aircraft owned and operated by the United States Department of Defense. Those on various types of leave, their spouses and other dependents can request this travel option, explains the Air Mobility Command of the United States Air Force.
Those wishing to travel using the Space-Available program must first check to see if they qualify, notes Air Mobility Command. As of November 2015, eligibility requirements include emergency, environmental morale and convalescent leave situations and hunting for a home at the location of a new assignment. Dependents of those deployed for over 120 consecutive days also qualify, as do retired military members and their families. All passengers must have all travel documents required by commercial airlines in order fly on Department of Defense aircraft.