Join Date: Sep 2002
Location: Between AUS, EWR, and YTO In a little twisty maze of airline seats, all alike.. but I wanna go home with the armadillo
Programs: CO, NW, & UA forum moderator emeritus. Eurobonus Millionaire
Posts: 38,610
You can probably cancel before you leave for the airport but it is certainly safer to cancel once you arrive and pass through security. Otherwise you are technically not passing the TSA drones with a valid boarding pass. If you are a PC member you can always show your card and ask for a gate pass bypassing this procedure altogether.