The No-Fly list of people who are not supposed to be allowed onto US airplanes is implemented by the airlines, who compare the name on the ticket with the names on the no-fly list and flag up any matches for additional checking - at minimum people with the same name as someone on the list have to go through extra security checks. This is flagged up by the airline printing some special indication on their boarding pass, which all passengers now have to show to get through security to the gate.

I recently flew inter-state on American Airlines from Chicago O'Hare, and was pleasantly surprised to learn that I could print out my own boarding pass before leaving home. Because of a problem with my primary computer I actually printed the boarding pass page to a file on disk, and used a different computer to send that file to the printer. The resulting piece of paper was sufficient to get me through security without my having to check in. I did have to show my ID, which was compared against the name on the boarding pass, but not against any other list. The boarding pass also contained a bar-code which the gate agent scanned immediately before allowing me to board the plane - I did not have to check in at the gate first.

At no time did anyone compare the name printed on the boarding pass with the name stored in the airline's computer. It used to be pretty hard for these to differ because the boarding pass was printed out directly by the airline at check-in, and the agent there would only issue the pass to someone whose ID matched the ticket. However with this nice convenience system there is nothing to stop someone from altering the information printed on a home-printed boarding pass - I could have changed the name on my pass and I'm confident that as long as the name matched that on my ID I would have been able to fly, even though the airline's computer thought that someone else was really the passenger.

It should be fairly obvious from the above how someone who is on the no-fly list can get to fly without triggering any special security procedures, providing they have a friend not on the list who is willing to buy them a ticket and print them out an edited boarding pass. It would also be just as easy to modify the date and time printed on a pass, and hence get anyone through security on a different date to the original ticket, although it would be very unwise to attempt to board a plane afterwards!

It's possible that you have to be a member of the AA frequently flier program to print your own boarding pass, but that makes no difference to the (in)effectiveness of the security.