Summary: In response to a congressional request, GAO evaluated the Federal Aviation Administration's (FAA) Civil Aviation Security Program to determine the effectiveness of its passenger screening process at airports with the highest security risk. GAO found that: (1) since the security measures at most airports are interrelated, if one measure fails, another measure is in place to support the failed measure; (2) the FAA policy on passenger screening does not ensure that airport and air carrier employees are not carrying dangerous weapons through the screening process; (3) FAA needs to improve accountability and control over personnel identification systems; (4) airport and air carrier employees do not always challenge unauthorized persons or require that all employees display their identification badges; and (5) although FAA requires perimeter barriers, due to the ineffectiveness of the challenge procedures, unauthorized personnel could gain access to these restricted areas. GAO believes that to improve security FAA should: (1) account for identification badges at high-risk airports; (2) reemphasize airline and airport employee responsibility to challenge the presence of unauthorized persons and stress the importance of properly displaying employee identification; and (3) evaluate the extent to which individual airlines should exempt employees from the passenger screening process.