Possible methods of entry
On one of the many news shows my son is surfing through, we saw a report this evening that mentioned that government agents attempting to board planes by gaining access to restricted areas or by approaching the plane on the tarmac were successful 80% of the time. Although passengers are pretty tightly policed (and agents had quite a bit of success smuggling simulated guns and explosives through screening devices too), it appears that airport security for employees resembles a sieve.