Targets for Terrorists: Post-9/11 Aviation Security

Targets for Terrorists: Post-9/11 Aviation Security

The air travel system remains one of the most high-profile targets for terrorists. This backgrounder examines efforts to improve aviation security since the 9/11 attacks.

September 7, 2006 12:41 pm (EST)

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Terrorists were targeting airliners with their attacks long before the 9/11 hijackings and the subsequent launch of the U.S. "war on terror." Despite heightened security measures, airliners remain an attractive target for terrorists, as evidenced by the revelation in August 2006 of a plot to simultaneously down as many as ten of them over the Atlantic Ocean. In order to counter the persistent and ever-changing threat of terrorism, experts say officials need to do more to ensure the safety of air travel.

Why are airliners attractive targets for terrorism?

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"You get a lot of victims at once. There is a lot of bang for the buck," says Steven Simon, the former senior director for counterterrorism at the National Security Council. "There is a particular horror attached to transportation attacks because passengers are in effect helpless in a situation like that." In addition, the dramatic nature of airliner attacks attracts media attention and can help inspire fear in the populace, two major aims of most terrorist operations.

Yet passengers seem unfazed by the prospect of terrorist attacks on planes. Since the 9/11 attacks, the Economist reports, commercial air traffic has risen by some 30 percent.

How has aviation security changed since the 9/11 attacks?

Shortly after the 9/11 terrorist attacks, Congress passed the Aviation and Transportation Security Act (PDF), which created the Transportation Security Administration (TSA) and mandated that federal employees be in charge of airport security screening. The TSA has implemented more thorough screening procedures for passengers and their baggage, whereby passengers go through metal detectors, carry-on bags are x-rayed, and checked baggage passes through an explosive detection system. Minor changes to these procedures—such as requiring passengers to remove their shoes or the more recent prohibition of carry-on liquids—have had some effect. But the real change, according to George Naccara, federal security director at Boston’s Logan Airport, has been the institution of "many layers of security," including measures that go beyond passenger screening, such as heightened police presence outside of airports and increased cooperation between airlines and security officials. Airport security expert Norman Shanks says these changes "have raised the standard of security of all airports in the United States, which was long overdue."

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In addition to checking passengers and their belongings at the airport, the TSA prescreens passengers. Airlines are required to submit lists of passengers to the TSA, which then compares the names to a watch list. This practice has been problematic: Civil liberties groups raised objections to the sharing of passenger data and watch lists were not always well maintained. To allay these concerns, the TSA developed the Secure Flight Program, a prescreening program that attempts to strike the proper balance between passengers’ rights and their security. Another program, called Registered Traveler, allows frequent flyers to volunteer background information and biometric identifiers, such as fingerprints, in order to facilitate their security screening. This program had a successful trial in 2005, but has yet to be fully implemented.

Several new measures designed to prevent hijackings also have been adopted. These include fortified cockpit doors, armed pilots on some flights, and an expansion of the Federal Air Marshals program, which places armed undercover officers on passenger flights. Experts say another important change in aviation security is an adjustment in passenger behavior. Since the 9/11 attacks, passengers are taking a more active role in preventing terrorists from carrying out their plots aboard airplanes.

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What are some of the criticisms of aviation security?

Some critics say that by focusing so heavily on screening passengers, security officials have left aircraft vulnerable to attack in other areas. Foremost among these, experts say, is air cargo security. In addition to carrying travelers’ baggage, the lower deck of many airliners holds a sizeable amount of air freight. Though 100 percent of passengers’ checked luggage is required to be screened for explosives, according to a Congressional Research Service report (PDF), only a small portion of the air cargo is ever inspected.

Others criticize the ease with which airline and airport employees bypass security checkpoints when entering secure areas. Some experts have called for the use of biometric identification for such access. There are also concerns over the potential of an attack by terrorists using a shoulder-fired anti-aircraft missile: In 2002 terrorists fired such a missile at an Israeli charter jet as it took off from Mombasa, Kenya. The Department of Homeland Security has commissioned prototypes of anti-missile systems but it remains unclear when, if ever, such systems will be implemented.  

Despite the heightened focus on passenger screening, it too remains a magnet for criticism. At a hearing of the House Committee on Transportation and Infrastructure, John Mica (R-FL), chairman of the Subcommittee on Aviation, lamented, "The TSA’s current baggage screening system continues to show no ability to adapt or keep pace with the ever-changing demands of the aviation industry. At the same time that the patchwork system is getting bogged down by its own inefficiencies, there is growing evidence that it does not even afford us more effective security screening." More advanced technologies could improve screening procedures, but the deployment of new devices has been slow. 

As for prescreening passengers, Shanks says, "In principle it’s a good idea, but in practice it doesn’t always turn out that way." The watch lists compared with passenger manifests are just lists of names. Ordinary passengers with names similar to ones on the list have at times been stopped, and Shanks says there’s little to stop a terrorist from creating a false identity. Homeland Security Secretary Michael Chertoff seems to agree. In an August 29 Washington Post op-ed, he called for screening measures that would allow U.S. officials access to such data as passengers’ cell phone numbers.

What else can be done to improve security?

One approach, called behavior pattern recognition (BPR), uses behavior clues to identify potential terrorists during passenger screening. Rafi Ron, former director of security at Tel Aviv’s Ben Gurion airport and now a security consultant working with the TSA to implement BPR programs at U.S. airports, says if BPR is widely implemented it will "add a very important security layer to our aviation [system]." The technique involves first identifying passengers exhibiting suspicious behavior, such as wearing heavy clothing on a warm day, excessive sweating, or using a pay phone in areas with cell phone reception. Individuals identified in this way are then selected for targeted interviews with a law enforcement officer who is trained to detect signs that a passenger is concealing something. Ron describes these interviews as "friendly conversations;" most are only a few minutes long. The vast majority of the passengers questioned like this are allowed to continue on their travels; the few passengers who arouse an officer’s suspicions are subjected to an hour-long interrogation and search. Naccara, who has used BPR at Logan Airport for three and a half years, says it works "extremely well."

The TSA is testing BPR under a program called Screening Passengers by Observation Technique, or SPOT. Ron says that while no terrorists have been netted, several criminals have been arrested. Yet the process is not foolproof: Shoe-bomber Richard Reid was targeted for an interview by a security guard before boarding a flight from Paris to Miami. The conversation aroused the guard’s suspicions, who referred Reid to French law enforcement for further questioning scrutiny. French officials, Ron says, did not properly search Reid, who was wearing a bomb during the entire interrogation.

Implementing advanced technology has been widely touted as a means of improving airport security.  There are a number of new technologies that may eventually be incorporated into the screening process. These include:

  • Backscatter X-rays can trace the contours of a person’s body and reveal any hidden objects, such as non-metallic weapons, plastic explosives, or drugs. Some critics argue these devices reveal too much and are an invasion of privacy, though filters can be added to protect a passengers’ modesty.
  • Trace-detection portals or “puffers” can be used to detect explosive residue on a passenger by blowing small bursts of air at the person being screened. These puffs are designed to dislodge molecules from a person’s body or clothing, and the air is sucked into a filter and analyzed for suspicious substances. The same method may be used on luggage.
  • Quadrupole Resonance Scanning is a way of identifying materials packed in passengers’ baggage. A scanner bombards a passenger’s suitcase with radio waves and examines the wavelengths of the energy emitted by the contents of the bag. This method has been used to detect some 10,000 different substances. 
  • Polygraphs, or lie detectors, as they often called, have long been used in other settings, but in 2006, the TSA began testing a polygraph-like system for passenger screening. In this new system, passengers enter a booth, place one hand on a sensor, and answer a series of questions on a touch screen. The sensor measures such things as blood pressure, pulse, and sweat levels, analyzing them to determine if the person is lying.  

While improved techniques and advanced technology can certainly help to make air travel safer, there is no magic bullet. "There will always be vulnerabilities," Naccara says, "We should never be satisfied; we should always be looking for improvements."

Do other countries have the same security measures as the United States?

No. Specific security measures vary from country to country. General standards for minimum security measures are dictated by the International Civil Aviation Organization (ICAO), but those standards are not always met. Even if foreign airports are screening 100 percent of passengers’ baggage, as the ICAO requires, Shanks says, “Other countries may be using technology that is not the best.” This might explain how in August 2006, a U.S. college student boarded a plane in Argentina with explosive powder and a stick of dynamite in his checked bag.

Some countries have security measures that surpass those of the United States. Tel Aviv’s airport is widely regarded as the safest in the world. There, airport officials interview every single passenger using the same BPR techniques that are currently being tested in the United States. Interviewing 100 percent of the passengers, Ron says, "has proven to be more effective than any other aviation security measure," but cultural and legal obstacles have prevented implementation of such a program in the United States.


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