[header] How to fly for free [title] Agree to be bumped. [step] Major airlines tend to overbook their flights to compensate for passengers who may not show up. If more passengers show up than can fit on the airplane, the airline will ask for volunteers to take a different flight. 
To show their gratitude, they usually offer travel vouchers you can use on future flights. Just wait for an airline representative to announce that your flight has been overbooked, and then head to the counter to ask about being bumped.