Through a contract with United Airlines , Argenbright operated passenger security checkpoints at Dulles International Airport , where five hijackers passed through before boarding American Airlines Flight 77 on September 11 , 2001 . United Airlines also contracted with Argenbright to manage its security operations at Newark Liberty International Airport , where the hijackers on United Airlines Flight 93 passed through
United Airlines Flight 93
United Airlines Flight 93
Argenbright Security