With the passage of the Aviation and Transportation Security Act (ATSA) in November 2001, TSA assumed responsibility for civil aviation security from the Federal Aviation Administration and for passenger and checked baggage screening from air carriers. As part of this responsibility, TSA oversees security operations at the nation’s more than 400 commercial airports, including establishing requirements for passenger and checked baggage screening, and ensuring the security of air cargo transported to, from, and within the United States. While TSA has operational responsibility for conducting passenger and checked baggage screening, TSA has regulatory, or oversight, responsibility for air carriers who conduct air cargo screening. While TSA took over responsibility for passenger checkpoint and baggage screening, as directed by ATSA, air carriers have continued to conduct passenger prescreening, which includes the process of checking passenger information against federal watch list data before flights depart. In accordance with the Intelligence Reform and Terrorism Prevention Act of 2004, TSA is developing a program to take over this responsibility from air carriers for passengers on domestic flights, and CBP has issued a proposed rule that would enable it to perform its identity-matching function for passengers on international flights traveling to or from the United States prior to flight departure. The prescreening of airline passengers—the process of identifying passengers who may pose a security risk before they board an aircraft—is one of many important layers of security that is intended to help officials focus security efforts on those passengers representing the greatest potential threat to civil aviation. Within DHS, TSA is responsible for ensuring that passenger prescreening is conducted before domestic flights—flights operating entirely within the United States—take off, while CBP has responsibility for conducting passenger prescreening for international flights operating to or from the United States. TSA is developing a program, in accordance with ATSA and the Intelligence Reform and Terrorism Prevention Act of 2004, through which TSA would assume the watch list matching function currently conducted by air carriers prior to domestic flight departures. TSA has named this prospective prescreening program Secure Flight. In accordance with security directives issued by TSA, air carriers—and not the U.S. government—currently match passenger-supplied reservation information (referred to as passenger name record (PNR) data), against the No Fly and Selectee Lists to prescreen passengers before domestic flights depart. According to TSA, the No Fly List includes the names of individuals considered to be known or suspected threats to civil aviation and are therefore precluded from boarding an aircraft traveling to, from, or within the United States, while the Selectee List includes the names of individuals who require additional security screening—which includes physical inspection of the person and a hand search of their luggage—prior to being permitted to board an aircraft. These lists are extracted from the Terrorist Screening Center’s (TSC) consolidated terrorist screening database (TSDB) and are exported to the air carriers through TSA. The current domestic prescreening process also requires that air carriers operate the Computer-Assisted Passenger Prescreening System (CAPPS), which identifies passengers for additional screening based on certain behavioral characteristics. The existing identity-matching component of DHS’s international aviation passenger prescreening process involves separate matching activities conducted by air carriers (prior to a flight’s departure and pursuant to TSA requirements) and by CBP (generally after a flight’s departure). As with domestic passenger prescreening, air carriers conduct an initial match of self-reported PNR data against the No Fly and Selectee Lists before international flight departures. CBP’s process, in effect, supplements the air carrier identity matching for international flights by comparing additional passenger information collected from passports (this information becomes part of Advanced Passenger Information System (APIS) data), against the No Fly and Selectee Lists and other government databases. Under current federal regulations for CBP’s prescreening of passengers on international flights, air carriers are required to provide the U.S. government with PNR data as well as APIS data to allow the government to conduct, among other things, identity matching procedures against the No Fly and Selectee Lists—which typically occur just after or at times just before the departure of international flights traveling to or from the United States, respectively. To address a concern that the federal government’s identity matching may not be conducted in a timely manner, in 2004, Congress mandated that DHS issue a proposed rule requiring that the U.S. government’s identity-matching process occur before the departure of international flights. CBP published this proposed rule in July 2006, and, if implemented, it will allow the U.S. government to conduct passenger prescreening in advance of flight departure, and will eliminate the need for air carriers to continue performing an identity- matching function for international flights. One of the most significant changes mandated by ATSA was the shift from the use of private-sector screeners to perform airport screening operations to the use of federal screeners (now referred to as TSOs). Prior to ATSA, passenger and checked baggage screening had been performed by private screening companies under contract to airlines. ATSA required TSA to create a federal workforce to assume the job of conducting passenger and checked baggage screening at commercial airports. The federal screener workforce was put into place, as required, by November 2002. Passenger screening is a process by which personnel authorized by TSA inspect individuals and property to deter and prevent the carriage of any unauthorized explosive, incendiary, weapon, or other dangerous item onboard an aircraft or into a sterile area. Passenger screening personnel must inspect individuals for prohibited items at designated screening locations. As shown in figure 1, the four passenger screening functions are: X-ray screening of property, walk-through metal detector screening of individuals, hand-wand or pat-down screening of individuals, and physical search of property and trace detection for explosives. Typically, passengers are only subjected to X-ray screening of their carry- on items and screening by the walk-through metal detector. Passengers whose carry-on baggage alarms the X-ray machine, who alarm the walk- through metal detector, or who are designated as selectees—that is, passengers selected by the CAPPS or other TSA-approved processes to designate passengers for additional screening—are screened by hand- wand or pat-down and have their carry-on items screened for explosives traces or physically searched. Checked baggage screening is a process by which authorized security screening personnel inspect checked baggage to deter, detect, and prevent the carriage of any unauthorized explosive, incendiary, or weapon onboard an aircraft. As shown in figure 2, checked baggage screening is accomplished through the use of explosive detection systems or explosive trace detection systems, and through the use of alternative means, such as manual searches, canine teams, and positive passenger bag match, when the explosive detection or explosive trace detection systems are unavailable. The passenger and checked baggage screening systems are composed of three elements: the people (TSOs) responsible for conducting the screening of airline passengers and their carry-on items and checked baggage, the technology used during the screening process, and the procedures TSOs are to follow to conduct screening. Collectively, these elements help to determine the effectiveness and efficiency of passenger and checked baggage screening. TSA’s responsibilities for securing air cargo include, among other things, establishing security rules and regulations covering domestic and foreign passenger air carriers that transport cargo, domestic and foreign all-cargo carriers that transport cargo, and domestic indirect air carriers. TSA is also responsible for overseeing the implementation of air cargo security requirements by air carriers and indirect air carriers through compliance inspections, while air carriers are required to inspect air cargo for weapons, explosives, or stowaways. Air carriers (passenger and all-cargo) are responsible for implementing TSA security requirements, predominantly through a TSA-approved security program that describes the security policies, procedures, and systems air carriers are required to implement. These requirements include measures related to the acceptance, handling, and inspection of cargo; training of employees in security and cargo inspection procedures; testing employee proficiency in cargo inspection; and access to cargo areas and aircraft. If threat information or events indicate that additional security measures are needed to secure the aviation sector, TSA may issue revised or new security requirements in the form of security directives or emergency amendments applicable to domestic or foreign air carriers. The air carriers must implement the requirements set forth in the security directives or emergency amendments in addition to those requirements already imposed and enforced by TSA. Air cargo ranges in size from one pound to several tons, and in type from perishables to machinery, and can include items such as electronic equipment, automobile parts, clothing, medical supplies, other dry goods, fresh cut flowers, fresh seafood, fresh produce, tropical fish, and human remains. Cargo can be shipped in various forms, including large containers known as unit loading devices that allow many packages to be consolidated into one container that can be loaded on an aircraft, wooden crates, assembled pallets, or individually wrapped/boxed pieces, known as break bulk cargo. Participants in the international air cargo shipping process include shippers, such as individuals and manufacturers; freight forwarders or regulated agents, who consolidate shipments and deliver them to air carriers; air cargo handling agents, who process and load cargo onto aircraft on behalf of air carriers; and passenger and all-cargo carriers that store, load, and transport air cargo. International air cargo may have been transported via ship, train, or truck prior to its loading onboard an aircraft. Figure 3 identifies cargo being loaded onto an aircraft for transport. According to DHS’s budget execution reports, TSA’s appropriations for aviation security have totaled about $20 billion since fiscal year 2004. In fiscal year 2004—the first year for which data was available—TSA received about $3.9 billion for aviation security programs. In fiscal year 2007, TSA received about $5.7 billion.