The terrorist attacks of September 11, 2001, and the response to those attacks have made aviation and airport security a focal issue for the past several years. On that day, teams of hijackers tied to al Qaeda, a radical Islamic terrorist group, commandeered four domestic flights in the United States, crashing two airplanes into the World Trade Center towers in New York City and one into the Pentagon near Washington, DC. The fourth crashed in a farm field in western Pennsylvania, presumably after passengers had learned of the terrorists’ intentions and attempted to regain control of the aircraft. Nearly 2,000 people lost their lives in the attacks. Immediately following the attacks, the United States government moved swiftly to pass the Aviation and Transportation Security Act (ATSA) (Public Law 107–171). ATSA established the Transportation Security Administration (TSA), giving it direct responsibility for conducting passenger and baggage screening using a workforce of federal security screeners.
I. Responsibility for Airport and Aviation Security
II. Passenger and Baggage Screening
III. Passenger Prescreening and Behavioral Observation
IV. Airport Security
V. In-Flight Security Measures
VI. Options for Protecting Aircraft from Shoulder-Fired Missiles
VII. Air Cargo Security
VIII. General Aviation Security
Responsibility for Airport and Aviation Security
Before 9/11, aviation security policies and practices in the United States had evolved out of an emerging need to address increasingly violent hijacking incidents in the early 1970s. Airlines were given the responsibility for mandatory passenger screening, which they, in turn, delegated to contract security firms. Physical security of the airport property, including perimeter security and access control systems for airport workers, however, was placed in the hands of airport operators. The Federal Aviation Administration (FAA) was responsible for regulating airport and airline security, although it had not issued regulations governing the contract security firms that conducted passenger screening. Such regulations had been proposed a year prior to the 9/11 attacks in response to a statutory mandate issued in 1996 (FAA 2000).
Following the 9/11 attacks, the U.S. Congress immediately began examining alternative models for aviation security. Lawmakers expressed considerable concern over low wages and high turnover rates among contract airport screeners. In 1999, the average hourly wage for airport screeners was $5.75, and many screeners did not receive additional benefits. Consequently, at several airports, annual screener attrition exceeded 100 percent (FAA 1999). Policymakers concluded that low pay and inexperience among screeners and lax oversight compromised aviation security. Congress learned that in Canada and in several European countries, both passenger screening and physical security of the airport property were instead the responsibility of airport operators, or in some cases government security forces, and not the airlines. Under these systems, screeners received more training and better pay than contract screeners in the United States, and limited data indicated that they performed better as well (United States General Accounting Office 2001). Under ATSA, the United States established a system under which passenger and baggage screening became the responsibility of the newly formed federal TSA, while airport physical security remained in the hands of the airport authorities. The TSA took over responsibility for regulating all aspects of airport and airline security from the FAA and was given broad authority to implement security measures to detect, prevent, and mitigate threats to aviation.
Passenger and Baggage Screening
Beginning in the early 1970s, the United States and other countries began deploying walk-through metal detectors (WTMDs) and carry-on baggage X-ray systems for preboarding screening. These technologies have served as the primary means for screening passengers for more than 30 years. By the mid-1980s, X-ray screening was also being used on a limited basis to screen checked baggage, usually on international flights, as a means to supplement procedures, known as positive passenger bag matching (PPBM), designed to ensure that passengers boarded with their baggage. By the late 1990s, the FAA had deployed about 100 explosives detection system (EDS) machines to screen high-risk baggage on a small number of international flights, but most checked bags were not physically screened (National Research Council 1999).
Following the 9/11 attacks, the United States mandated that all checked baggage undergo explosives detection screening using either EDS machines, which rely on the same principles at computed tomography (CT) scanners widely used in the medical field; explosives trace detection (ETD) systems, which utilize chemical analysis techniques to detect trace amounts of explosives residue or vapors; or other approved methods (see 49 U.S. Code, Sec. 44901). Efforts remain underway to integrate bulky EDS machines into airport baggage handling systems to improve the efficiency of screening the large amount of checked baggage processed at U.S. airports.
While these actions are addressing the threat of explosives placed in checked baggage, there has been growing concern over explosives carried into the aircraft cabin by passengers or in carry-on items. The 9/11 Commission (2004) formally recommended that the TSA give priority attention to implementing technology and procedures for screening passengers for explosives, and provisions to improve checkpoint technologies to detect explosives were included in the Intelligence Reform and Terrorism Prevention Act of 2004 (Public Law 108–458). In response, the TSA initially pilot tested walkthrough trace detection portals, or puffer machines, and implemented procedures for conducting pat-down searches of passengers for explosives. Full deployment of the trace detection portals, for use in secondary screening of selected passengers, had been part of the TSA’s original strategy for screening passengers for explosives. The machines, however, suffered from reliability issues blamed largely on dirt and humidity in the airport environment (Fiorino, Compart, and Wall 2010).
The TSA has since changed its strategy, focusing instead on whole-body imaging (WBI) technologies, also referred to as advanced imaging technology or AIT, that utilize either X-ray backscatter or millimeter wave imaging techniques to screen passengers and detect threat items concealed underneath clothing. The TSA has implemented procedures, including remote monitoring and privacy filters, to protect passenger identity and dignity and to prevent the storage of passenger images. Privacy advocates have nonetheless raised objections about the use of these screening devices, particularly as a primary screening method (Sparapani 2006).
The TSA is also investing in advanced technology (AT) X-ray equipment, capable of providing multiple view angles and automated threat detection capabilities to improve the screening of carry-on items, and handheld bottled liquids scanners to screen for liquid explosives. The need for bottled liquid screening capabilities emerged following a foiled plot to bomb airliners departing the United Kingdom for North American airports using homemade liquid explosives concealed in soft drink bottles that was uncovered in August 2006. Artful concealment of explosives and other threats carried by passengers remains a key concern. The December 25, 2009, attempted bombing of an international airline flight on approach to Detroit, using an explosive device concealed in the suspect’s underwear, reinvigorated debate over policies and strategies for detecting explosives on passengers and in carry-on items. In response, the TSA has pushed for accelerated deployment of WBI systems and other checkpoint screening technologies (Karp 2010).
The cost of passenger and baggage screening and screening technologies, which totaled about $4.5 billion in fiscal year 2010, is paid in part by security fees charged to airlines and airline passengers and in part by general tax dollars collected by the federal government.
Passenger Prescreening and Behavioral Observation
Aviation security measures also rely on intelligence information to prevent suspected terrorists from boarding aircraft or to subject persons that may pose a security threat to additional screening. Prior to the 9/11 attacks, the FAA maintained a small “no-fl y” list of known terrorists. Airlines were to deny boarding to any individuals on this list, however none of the 9/11 hijackers were on the list which, at the time, contained only 12 names (9/11 Commission 2004). After 9/11, the list was greatly expanded, and as of 2008 was reported to consist of about 2,500 names (TSA 2008a). The no-fl y list is a subset of a larger terrorist screening database (TSDB), a list of about 400,000 individuals maintained by the Terrorist Screening Center (TSC), a unit of the Federal Bureau of Investigation (FBI). The TSDB is comprised of names of suspected and known terrorist compiled from domestic law enforcement databases and information on international terrorists compiled within the Terrorist Identities Datamart Environment (TIDE). The TIDE is a repository of foreign intelligence information on suspected terrorist operatives maintained by the National Counterterrorism Center (NCTC).
The TSA’s Office of Intelligence continually updates the no-fl y list by reviewing derogatory information contained in the TSDB to pinpoint those individuals believed to pose a specific threat to aviation. It also maintains a second larger list, known as the automatic selectee list, of individuals with possible ties to terrorism who are required to undergo additional checkpoint screening. In the past, the no-fl y and automatic selectee lists were provided to the airlines, which were responsible for checking passenger names against these lists. However, the TSA has now implemented a system called Secure Flight, under which airlines provide passenger data, including items such as address and date of birth, to the TSA, which checks this information against the lists and notifies the airlines electronically of a match.
Additionally, airlines continue to utilize the Computer Assisted Passenger Prescreening (CAPPS) system, developed by the FAA in the 1990s, to evaluate passenger records for potentially suspicious characteristics, such as buying a one-way ticket using cash. Passengers determined to be of elevated risk based on the analysis performed by CAPPS may also be selected for secondary screening measures.
The TSA also deploys Behavior Detection Officers (BDOs) to observe passengers for possible indicators of hostile intent as part of a program known as Screening Passengers by Observation Techniques (SPOT). While the TSA has implemented SPOT at most major airports, government auditors found that the program has not been validated (United States Government Accountability Office 2010), and behavioral scientists have raised questions over the merits of the program (Weinberger 2010).
Whereas the TSA is responsible for prescreening and screening airline passengers, airport operators, with the assistance of state and local law enforcement, are responsible for the physical security of airport property including perimeter security and surveillance measures, access controls, and law enforcement support. Although the TSA (2006a) has published guidelines for integrating security elements in the design of airport terminals and facilities, no formal standards exist and solutions are tailored to the needs of specific airports. Since 9/11 many airports have invested in security technologies to enhance surveillance capabilities and improve perimeter protection. Airport security systems may include closed circuit television (CCTV) cameras, infrared sensors and thermal imaging cameras, computer vision systems to detect and alert security personnel regarding possible threats, ground surveillance radar, ground vehicle tracking, and integrated security solutions to tie together assorted sensors and surveillance technologies.
Airport operators also have the responsibility for coordinating law enforcement presence and support to intervene in security incidents as necessary and typically do so through formal arrangements with local or state law enforcement agencies. The TSA has entered into agreements at many airports to partially reimburse these law enforcement agencies for providing federally mandated coverage and law enforcement assistance to checkpoint screeners.
Airport operators are also responsible for implementing access control measures and issuing access credentials to airport workers. Airport workers must pass TSA criminal history records checks (CHRCs) and terrorist threat assessments before gaining unescorted access to secured areas. There has been considerable interest in implementing biometric credentials for airport access controls. While various biometric credentialing systems are being considered and evaluated for authenticating the identities of armed law enforcement officers, airline crews, and airport workers, uniform standards for biometric aviation security credentials have not been established and the use of biometrics in airport security is still relatively limited.
In-Flight Security Measures
ATSA included language requiring the installation and use of reinforced cockpit doors on passenger airliners. Other in-flight security measures used in some cases or under consideration include secondary flight deck barriers, video monitoring of the airline cabin from the cockpit, wireless devices for communication between pilots and flight attendants, and uninterruptable transponders that continuously report aircraft position and cannot be disabled by hijackers. Basic self defense training is provided by the airlines and the TSA offers voluntary advanced self defense training programs for pilots and flight attendants.
Since 9/11, the United States has deployed thousands of armed federal air marshals. Although the total number in the Federal Air Marshal Service (FAMS) is classified, air marshals typically work undercover in teams and, by law, are required to be on every flight considered high risk (49 U.S. Code, Sec. 44917). Prior to the 9/11 attacks, the number of air marshals had been reduced to 33 and deployments were limited to a small number of international flights (9/11 Commission, 2004). While FAMS expanded significantly following 9/11 and had an annual budget of almost $900 million in 2010, some media reports have raised concerns that FAMS cover only a very small percentage of daily flights (Griffin, Johnston, and Schwarzchild 2008).
In addition to deploying FAMS, considerable policy debate following the 9/11 attacks centered on whether allowing pilots to receive special training and authorization to carry firearms in the cockpit could serve to deter and prevent aircraft hijackings. Despite concerns raised by some aviation safety experts over the introduction of firearms in the cockpit, in 2002 the United States enacted legislation creating the Federal Flight Deck Officer (FFDO) program. Under the program, volunteer airline pilots that pass background checks receive firearms training and are issued a handgun to be used only on flights to protect the cockpit from hijackings and other threats. While the program has trained about 10,000 pilots through 2009 at an annual cost of about $25 million, pilot groups have complained that the remote location of the training site and other procedural requirements of the program have discouraged additional pilots from participating.
Options for Protecting Aircraft from Shoulder-Fired Missiles
On November 28, 2002, terrorists launched two shoulder-fired missiles at an Israeli charter jet departing Mombasa, Kenya. Following the incident, the United States Department of Homeland Security (DHS) initiated a program examining the feasibility of adapting missile protection systems deployed on some military aircraft for use on passenger jets. While the program resulted in the certification of two aircraft-based systems that can redirect a heat-seeking missile by focusing a laser on the missile’s tracking system, these countermeasures have not been mandated and airlines have not voluntarily installed them on fleet aircraft. Other concepts for protecting airliners, including ground-based missile countermeasures and anti-missile systems installed on unmanned patrol aircraft deployed in airspace around an airport, have also been studied on a limited basis. The future utilization of these technologies remains uncertain, although there is still some particular interest in equipping airliners contracted to carry military troops into hostile areas with certified anti-missile systems. At present, however, the main deterrents against shoulder-fired missile attacks targeting civilian aircraft are law enforcement patrols and surveillance of likely launch sites around airports.
Shoulder-fired missiles remain a considerable security concern because they are widely proliferated on the black market and have the capability to down airliners flying below about 15,000 feet, making them a potential threat at considerable distances from an airport, sometimes as far away as 30 to 40 miles. With increased security to prevent aircraft bombings and hijackings, some experts fear that terrorists may resort to shoulder-fired missile attacks.
Air Cargo Security
Amid heightened security to screen passengers and baggage, concerns have also been raised over the possibility that terrorists may instead attempt to place explosives in air cargo. The Implementing Recommendations of the 9/11 Commission Act of 2007 (9/11 Act, Public Law 110–153) requires the physical screening of all cargo placed on passenger aircraft by August 2010. The TSA has addressed this requirement by developing the Certified Cargo Screening Program (CCSP), an approach that relies heavily on shippers, cargo consolidators, and freight forwarders to carry out much of the operational aspects of screening cargo, often at off -airport sites in conjunction with enhanced supply-chain security measures to prevent tampering with cargo after screening has been conducted. While the TSA maintains that this approach meets the requirements of the legislation, some have argued that the TSA should instead play a more direct role in conducting or overseeing screening operations, and that the screening should take place in closer proximity to locations where cargo is loaded on to passenger airplanes. Owing to the size of bulk and palletized cargo shipments, EDS has a more limited role in cargo screening, particularly at airport locations, and solutions are focusing on extensive use of ETD and canine explosives detection teams to efficiently screen air cargo for explosives.
The 9/11 Commission (2004) also recommended deploying at least one hardened, blast-resistant, cargo container on every passenger airliner. The 9/11 Act required the DHS to complete an evaluation of its hardened cargo container pilot program and, based on this evaluation, carry out a risk-based deployment of hardened cargo containers for use on commercial flights. Under this provision, the cost of acquiring, maintaining, and replacing hardened containers would be provided for by the DHS. While the pilot program has been completed, the future direction for operational deployment of hardened cargo containers remains uncertain.
In addition to improving the screening of cargo placed on passenger aircraft, regulations have been issued to improve security for all-cargo operations and protect against unauthorized access to large all-cargo aircraft. Under existing cargo security rules, secured areas of airports have been expanded to include cargo operations areas. Background checks and security threat assessments are required for all workers with access to air cargo, including an estimated 51,000 off -airport employees of freight forwarding companies. Also, under these regulations, an industry-wide database of known shippers was established and is maintained by TSA to allow freight forwarders and airlines to vet cargo shipments, allowing only cargo received from established known shippers to travel on passenger airplanes (TSA 2006b).
General Aviation Security
Although aviation security measures have focused primarily on protecting passenger airliners, some experts have raised concerns that terrorists may try to avoid detection by using nonairline general aviation aircraft to carry out a 9/11 style attack, deliver a nuclear or radiological weapon to its target, or to dispense a chemical or biological agent over a populated area or major outdoor event. Securing general aviation operations continues to be a significant challenge because of the diversity of operations, aircraft, and airports. Measures put in place thus far, such as the Airport Watch program and the TSA’s general aviation security guidelines (TSA 2004), rely heavily on the vigilance of the pilot community to detect and report suspicious activity.
Flight training providers must verify citizenship and confirm that background checks have been properly completed by the TSA before providing training to foreign nationals (see Title 49, Code of Federal Regulations [CFR] Part 1552). Charter pilots operating aircraft weighing more than 12,500 pounds must pass background checks, and charter operators must implement security programs to protect aircraft from unauthorized access. Passengers flying on very large charter jets must be screened, and charter and private aircraft operators must adhere to special security procedures when operating at commercial passenger airports. All inbound and outbound international flights must send advance passenger and crew manifest information to U.S. Customs and Border Protection (CBP) which carries out terrorist watchlist checks and targeted screening of these names.
Security-related airspace restrictions affecting general aviation operators are most prevalent in the Washington, DC, area, where the city is encircled by a 15-mile-radius flight-restricted zone (FRZ) in which general aviation operations are significantly limited, and a larger special flight rules area (SFRA) where pilots must strictly adhere to special air traffic control procedures (Title 49 CFR Part 1562). In August 2005, the TSA implemented a security plan permitting a small number of general aviation flights— mostly large charter and corporate operations—to resume at Washington Reagan National Airport (DCA) which is located at the center of the FRZ. Operations at smaller GA airports located within the FRZ are highly restricted, requiring pilots to undergo background checks and adhere to special airspace security protocols. Since 9/11, flight restrictions have also been put in place at various times over New York City, Chicago, and elsewhere. General aviation pilots have been restricted from flying below 18,000 feet over Disney theme parks and over stadiums during major sporting events, and within 10 miles of a site during a presidential visit.
The TSA remains particularly concerned over the security of large general aviation aircraft. In October 2008, the TSA (2008b) proposed a variety of security measures for operators of all large general aviation aircraft, weighing more than 12,500 pounds, including privately owned, fractionally owned, and corporate aircraft. The measures proposed included CHRCs for all flight crew members, terrorist watch-list checks of all passengers, security inspections of aircraft, and biannual security compliance audits. In addition, operators of all aircraft weighing more than 45,500 kg (roughly 100,000 pounds) would be required to screen passengers and their accessible property. Similar security measures are already required for charter operators. General aviation operators and advocacy groups expressed considerable concern over the burden that would be imposed by these proposals. The TSA has since decided to revise its proposal based on additional input from general aviation interests. This, like many other aspects of aviation and airport security, continues to evolve at a rapid pace in response to changes in threats and vulnerabilities and shifting federal policies and strategies.
Although U.S. policies and strategies regarding aviation security continue to evolve, they have been predicated on a risk-based framework. This risk-based approach relies on expert judgment to evaluate the three core components of security risk: perceived threats, system vulnerabilities, and the potential consequences of various attack scenarios. Based on analyses of these risk factors, policies and strategies continue to evolve to allocate limited resources (including funding, personnel, and technology) in a manner that seeks to minimize security risk across the various sectors of the aviation system. As discussed, these sectors include air cargo operations and general aviation activity in addition to commercial passenger airports and airlines, which remain the primary focus of aviation security policy.
Aviation security relies on a multilayered strategy to protect high-risk components of the air transportation system. For example, commercial airline flights are protected by several layers of security that include passenger prescreening; passenger and baggage screening; and in-flight security measures such as hardened cockpit doors, air marshals, and armed pilots. A multilayered approach is more resilient to potential threats by including complementary security measures which, in combination, significantly reduce the probability that an individual or group could successfully carry out an attack.
Within this risk-based, multilayered framework, aviation security policies and strategies seek to strike a balance between effectively reducing security risk to acceptable levels while minimizing disruptions to air travel and commerce that may arise when various security measures are implemented and while taking appropriate steps to protect the privacy and dignity of the traveling public. Striking an appropriate balance between adequate levels of security and the efficient transportation of passengers and goods through the aviation system remains an ongoing challenge.
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