Re:When Airlines Screw Up Your Flight, AirHelp (YC W14) Gets...
by saryant on Wednesday March 05, 2014 @03:47PM
(#7349765)
If it's involuntary, you are owed cash, unless you're denied for weight/balance reasons in which case nothing is due, or you're rebooked on a flight within the hour. If it's voluntary, everything is at the airline's discretion.
United's official rules: http://flyerguide.com/index.php/S*UAL/DENIED-IDB