Originally established as the Sky Marshal program in the 1970s to counter hijackers, the Aviation and Transportation Security Act expanded FAMS’s mission and workforce in response to the September 11, 2001, terrorist attacks and mandated the deployment of federal air marshals on high- security risk flights. Within the 10-month period immediately following September 11, 2001, the number of air marshals grew significantly. Also, during years following the 2001 attacks, FAMS underwent various organizational transfers. Initially, FAMS was transferred within the Department of Transportation from the Federal Aviation Administration to the newly created TSA. In March 2003, FAMS moved, along with TSA, to the newly established Department of Homeland Security. In November 2003, FAMS was transferred to U.S. Immigration and Customs Enforcement (ICE). Then, about 2 years later, FAMS was transferred back to TSA in the fall of 2005. FAMS is one layer among multiple layers of aviation security. For example, prospective passengers are prescreened against applicable records in the Terrorist Screening Center’s consolidated watch list. Passengers and baggage are also physically screened. Air marshals generally are characterized as being the last line of defense within the layered aviation-security framework. In this regard, FAMS officials stressed that air marshals constitute the only in-flight security layer deployed on the basis of risk. FAMS deploys thousands of federal air marshals to a significant number of daily domestic and international flights. In carrying out this core mission of FAMS, air marshals are deployed in teams to various passenger flights. Such deployments are based on FAMS’s concept of operations, which guides the agency in its selection of flights to cover. Once flights are selected for coverage, FAMS officials stated that they must schedule air marshals based on their availability, the logistics of getting individual air marshals in position to make a flight, and applicable workday rules. At times, air marshals may have ground-based assignments. On a short- term basis, for example, air marshals participate in Visible Intermodal Prevention and Response (VIPR) teams, which provide security nationwide for mass transit systems other than aviation. Also, air marshals participate in Joint Terrorism Task Forces led by the Federal Bureau of Investigation. Good marksmanship is considered a necessity for air marshals, particularly given the unique environment of the core mission—the relatively tight confines of an airplane, coupled with the presence of numerous passengers (“bystanders”) and the possibility of air turbulence that creates an unstable “shooting platform” (see fig. 1). Thus, according to TSA, air marshals have the highest marksmanship standard in the federal government and also must be recertified on their firearm every quarter. To preserve their anonymity on covered flights, air marshals are to blend in with other passengers by dressing appropriately and performing their duties discreetly without drawing undue attention. FAMS’s operational approach (concept of operations) is based on risk- related factors, such as assessments of threat, vulnerability, and consequences. FAMS is guided by the provisions of the Aviation and Transportation Security Act that specify the deployment of federal air marshals on flights presenting high-security risks, such as nonstop, long- distance flights targeted on September 11, 2001. FAMS seeks to maximize coverage of high-risk flights by establishing coverage goals for 10 targeted critical flight categories. In order to reach these coverage goals, FAMS uses a scheduling process to determine the most efficient flight combinations that will allow air marshals to cover the desired flights. FAMS management officials stressed, however, that the overall coverage goals and the corresponding flight schedules of air marshals are subject to modification at any time based on changing threat information and intelligence. Following the attacks of September 11, 2001, FAMS developed a risk- based concept of operations for deploying air marshals on U.S. commercial passenger air carriers. Because there are many more U.S. air carrier flights each day than can be covered by air marshals, FAMS relies on the methodology outlined in its concept of operations to assign air marshals to flights with the highest security risks. Under this approach, FAMS considers the following risk-related factors to categorize each of the approximately 29,000 domestic and international flights operated daily by U.S. commercial passenger air carriers into risk categories—high risk or lower risk: Threat (intelligence): Available strategic or tactical information affecting aviation security is considered. Vulnerabilities: Although FAMS’s specific definition is deemed to be sensitive security information, DHS defines “vulnerability” as a physical feature or operational attribute that renders an entity open to exploitation or susceptible to a given hazard. Consequences: FAMS recognizes that flight routes over certain geographic locations involve more potential consequences than other routes. FAMS attempts to assign air marshals to provide an on-board security presence on as many of the flights in the high-risk category as possible. However, other considerations can make covering only high-risk flights impractical from a scheduling perspective and potentially predictable to an adversary. Therefore, for purposes of scheduling efficiency and adversary uncertainty, FAMS may deploy some air marshals on lower-risk flights. FAMS has established a scheduling process intended to maximize the coverage of high-risk flights and meet the agency’s desired coverage goals for 10 targeted critical flight categories. FAMS’s Domestic Planning Branch (within the Systems Operation Control Division) is responsible for scheduling air marshals to domestic missions. During the course of a year, the Domestic Planning Branch must prepare schedules for 13 roster periods of 28 days each. According to FAMS officials, each 28-day schedule takes approximately 3 weeks to prepare. The Domestic Planning Branch prepares each domestic schedule using an automated scheduling tool. As part of the scheduling process, each FAMS field office is responsible for making available a specific percentage of their air marshals on a daily basis to cover targeted critical flights (both domestic and international flights) in the roster periods. FAMS utilizes the automated scheduling tool to determine the most efficient flight “pairings” of departure and return flights that will bring an air marshal back to his or her starting point and that would be within the parameters for mission assignment and rest for the air marshal. FAMS officials also perform other checks on the fairness or appropriateness of the schedules, such as ensuring that certain flights are not being covered repeatedly by the same air marshals. FAMS officials noted that the schedules for deploying air marshals are altered as needed to cover specific, high-threat flights. For example, in August 2006, FAMS increased its coverage of international flights in response to the discovery, by authorities in the United Kingdom, of specific terrorist threats directed at flights from Europe to the United States. However, the officials added that a shift in resources of this type can have consequences because of the limited number of air marshals. FAMS officials noted that international missions require more resources than domestic missions partly because the trips are of longer duration. In its 2003 PART review of FAMS, OMB concluded that an independent evaluation should be conducted to assess FAMS’s performance related to aspects of the agency’s concept of operations—particularly aspects involving flight coverage risk categories, the distribution of covered flights, and target levels of coverage. The Homeland Security Institute, a federally funded research and development center, performed this evaluation and issued a final report in July 2006. The report concluded that FAMS’s approach for achieving its core mission of providing an onboard security presence for flights, as detailed in the agency’s concept of operations, was reasonable and made several recommendations for enhancements. The Homeland Security Institute recommended, for example, that FAMS increase randomness or unpredictability in selecting flights and otherwise diversify the coverage of flights within various risk categories. As of October 2008, FAMS had implemented or had ongoing efforts to implement the recommended enhancements. In a July 2006 report, the Homeland Security Institute specifically noted the following regarding FAMS’s overall approach to flight coverage: FAMS applies a structured, rigorous approach to analyzing risk and allocating resources. The approach is reasonable and valid. No other organizations facing comparable risk-management challenges apply notably better methodologies or tools. As part of its evaluation methodology, the Homeland Security Institute examined the conceptual basis for FAMS’s approach to risk analysis. Also, the institute examined FAMS’s scheduling processes and analyzed outputs in the form of “coverage” data reflecting when and where air marshals were deployed on flights. Further, the Homeland Security Institute developed and used a model to study the implications of alternative strategies for assigning resources. We reviewed the Homeland Security Institute’s evaluation methodology and generally found it to be reasonable. In a 2008 PART reassessment of FAMS, OMB also reported that the Homeland Security Institute’s evaluation employed quality evaluation methods and was comprehensive in scope. Further, OMB noted that an interagency steering group—which was convened by the Homeland Security Institute and met in conference in April 2006—also had reviewed FAMS’s concept of operations and considered it to be reasonable. In addition to FAMS and Homeland Security Institute participants, the interagency steering group consisted of representatives from various law enforcement and counterterrorism agencies, which included the Federal Bureau of Investigation, U.S. Customs and Border Protection, the Transportation Security Administration, the Federal Aviation Administration, the Homeland Infrastructure Threat and Risk Assessment Center, U.S. Northern Command/North American Aerospace Defense command, and the National Counterterrorism Center. In its July 2006 report, the Homeland Security Institute made several recommendations for enhancing FAMS’s approach for deploying air marshals on flights. As presented in table 1, FAMS had implemented or had ongoing efforts to implement all of the recommended enhancements, as of October 2008. In reference to the core mission of FAMS, the Homeland Security Institute’s recommendations regarding two processes—the filtering process for selecting flights and the allocation process for assigning air marshals to flights—are particularly important.