How the NSA obtains and uses airline reservations (2013)
I first heard this 13 years ago.  A friend visited an airline, and had a set of cables pointed out to him: "That's the feed to the NSA".I thought it was well known that the NSA had feeds into the airline reservation system.  We know for sure that the CBP gets data from all flights which overfly the US, or which might overfly the US.There are well known stories about planes making unscheduled landings in the US (emergency, storm, delays, etc).  Cue CBP opening the front doors, walking down the aisle, and pulling one guy off the plane."Sorry sir, you are forbidden to enter the US, and you have just done so illegally.  You're under arrest".Except for most people, we haven't cleared customs, and haven't tried to enter the States.  So the rest of the passengers are "OK".  Mostly.This is known as having your cake and eating it, too.