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Airport Imaging Scanners: How Effectiveness and Emerging Technologies Factor into Legal and Policy Debates
By Dillon Martinson, JD
Airport Scanners

Millimeter wave scans (left panels) create images that resemble a fuzzy photo negative. Backscatter scans (right panels) resemble chalk etchings. Both produce anatomically correct images, raising privacy concerns.

Terrorists intent to target planes has not diminished despite increased security in the nearly 10 years since 9/11. Instead, we have seen multiple plans and attempted attacks using liquid explosives concealed in shoes, underwear, printer cartridges, breast implants, and even dogs. To counter this adaptive adversary, the Transportation Security Administration (TSA) has sought to replace traditional metal detectors—which cannot detect liquid explosives—with advanced imaging technology (AIT) scanners. However, this move has been met with considerable controversy, raising privacy, legal, and policy questions. Privacy and security are often thought of as being on opposite ends of the spectrum, where strengthening one implies weakening the other. This article suggests that what is missing from these discussions is a focus on effectiveness and emerging technologies. These two subjects not only impact the law and policy behind air travel security, they also demonstrate how security is not just about trade-offs. We actually can enhance security and privacy concurrently.

About AIT Scanners

TSA employs two types of AIT scanners, millimeter wave and backscatter. Millimeter wave uses radio frequency energy from two spinning antennas to generate a black and white three-dimensional image that resembles a fuzzy photo negative. Backscatter projects low level X-ray beams over the body to produce a two-dimensional image that resembles a chalk etching (Transportation Security Administration: Advanced Imaging Technology, How it Works, n.d.). Both AITs produce anatomically correct images, raising significant privacy concerns and references to a “virtual strip search.” Fourth Amendment Given the privacy concerns, some have questioned whether AITs violate a passenger's Fourth Amendment rights. The Fourth Amendment requires the government to respect “[t]he right of the people to be secure…against unreasonable searches and seizures” (U.S. Constitution, Amendment IV). Searches are typically unconstitutional absent individualized suspicion of wrongdoing. However, under the administrative search doctrine, blanket suspicionless airport searches are constitutional so long as they are reasonable (U.S. v. Davis, 1973). While no court has ruled on the constitutionality of AIT scanners, their rulings on similar security screening measures will likely set the standard by which AITs will be judged. Since the Supreme Court has yet to directly weigh in on the constitutionality of airport screenings, we look to the Circuit Courts for guidance. There are two prevailing tests in the lower courts for determining whether an airport security screening search is constitutional under the Fourth Amendment. In the 3rd Circuit, a suspicionless airport security search is permissible when the court finds a favorable balance between the gravity of the public's concern served by the search, the degree to which the search advances the public interest, and the severity of the interference with individual liberty (U.S. v. Hartwell, 2006). In the 9th Circuit, a suspicionless airport search is constitutionally reasonable provided that it is no more extensive nor intensive than necessary, in the light of current technology, to detect the presence of weapons or explosives and that it is confined in good faith to that purpose (U.S. v. Aukai, 2007). Though both tests vary in rationale, the outcome of each will likely hinge on whether the AIT search is more intrusive than it needs to be, implicating questions of effectiveness and privacy. Let us briefly examine the legal and policy implications of each in turn.


Both courts tests incorporate an effectiveness prong—examining the necessity or degree to which AIT scanners actually detect the presence of liquid explosives that they are designed to detect. Absent clear evidence of ineffectiveness, courts are likely to find that the determination of whether AITs are effective is a matter for the government agency, not the courts. The courts determination of effectiveness is “not meant to transfer from politically accountable officials to the courts the decision as to which among reasonable law enforcement techniques should be employed to deal with a serious public danger” (Michigan Dept. of State Police v. Sitz, 1990). In Fourth Amendment analyses, the courts have given the government much deference, recognizing that the choice among reasonable alternatives for searches should remain with government officials who have a unique understanding of the threat and responsibility for limited public resources (Michigan Dept. of State Police v. Sitz, 1990). The effectiveness of AIT scanners is more of a policy question than a purely legal one, but it is no less important of an issue. The Department of Homeland Security asserts that AIT scanners are effective, capable of revealing weapons, explosives, drugs, and other contraband, whether it is liquid, powder, metallic, or non-metallic. In particular, Secretary Napolitano stated that AIT scanners would have detected the type of liquid explosive used in the attempted bombing on Christmas Day, 2009. But a GAO report found that “it remains unclear whether the AIT would have been able to detect the weapon Mr. Abdulmutallab used in his attempted attack” (U.S. Government Accountability Office, 2010). The public has a right to know if AIT scanners are effective. First, TSA spent $29.6 million on explosive trace portals (ETPs), or “puffers,” designed to detect traces of explosives on passengers. But TSA found that the machines broke down too often and did not meet the “requirements for operational suitability” and they were phased out (Blogger Paul, 2009). Having spent $338 million on AIT scanners, what evidence does the public have that their tax dollars will have a greater return on investment for AITs than they did on the ETPs? Second, the public has a right to know if AIT scanners are effective because TSA has included the public in its rationale for AIT use. On its home page for AIT, TSA cites a CBS poll stating that 4 out of 5 Americans support the use of AIT technology at airports (Transportation Security Administration: Advanced Imaging Technology Home, n.d.). Regardless of the merits of this poll, this shows that the public's opinion of TSA security measures is at least part of the equation for determining what security measures TSA will implement. If the public is going to play a role in determining security measures, which it should, it needs to have informed opinions. When four professors at the University of California, San Francisco sent a letter to the President's Office of Science and Technology Policy expressing concern about the health risks of AITs, they received a detailed response from the Food and Drug Administration. We need the same type of response from TSA on the effectiveness of AIT scanners—one that addresses concerns with real data but does not reveal information that would pose a security threat. Passenger support of screening procedures not only improves TSA's public image; it also improves security.


Let us now examine the intrusiveness prong to our Fourth Amendment analysis. Here the courts have looked at the following elements: whether procedures are well-tailored to reduce intrusion, if all passengers receive the same screening, the public nature of the search, the length of detention, and if passengers are on notice that they will be searched (U.S. v. Hartwell, 2006). To improve privacy, millimeter wave technology blurs all facial features, and backscatter technology has an algorithm applied to the entire image. In addition, the TSA Transportation Security Officer reviews the AIT image in a remote location, and as soon as the individual is cleared, the image is automatically deleted. In addition, passengers are made aware that they will receive the AIT scan as a primary screening—as opposed to a random secondary screening—and that the screening is of short duration and in a public place. But there is more to this analysis, including the language “in the light of current technology.” Just how commonly known and vetted a technology must be is not an area settled in the law. However, the language suggests that AIT scanners could be unconstitutional if other technologies that are equally effective but less intrusive are available, though the court is likely to grant the government much deference here as well. Other less intrusive technologies do exist. TSA is currently testing an imaging technology developed by Iscon that uses thermal-boosted infrared detection to reveal contraband. Most importantly, the imaging technology displays concealed objects on top of passengers clothes regardless of where they are hidden, thereby eliminating many privacy concerns (Iscon, n.d.). TSA has not yet released any results on the testing of the Iscon system. Rapiscan, maker of the backscatter machine, and L-3, developer of the millimeter wave machine, are developing software patches that provide an image-free solution. The software would automatically detect contraband, highlighting the area of concern over a generic mannequin-like figure. This will remove the need for TSA officers to review most images, thereby improving privacy, efficiency, and costs. Other technologies are being developed that can detect objects hidden in body cavities and shoes, which current AIT technologies cannot detect.


AIT scanners are probably no more intrusive than necessary, meaning they are reasonable under the Fourth Amendment. However, the analysis shows that effectiveness and technology do factor into the legal and policy debate. As we look to the future, we should focus on developing real-world technological solutions that integrate privacy and security in effective ways. This will ensure airport screening is both legally and politically sound while improving security and privacy.


Blogger Paul. (May 21, 2009). The TSA Blog: Explosive Trace Detection. Retrieved from http://blog.tsa.gov/2009/05/explosive-trace-detection.html

Iscon Imaging. (n.d.). Retrieved from http://www.isconimaging.com/

Transportation Security Administration: Advanced Imaging Technology, How It Works. (n.d.). Retrieved from http://www.tsa.gov/approach/tech/ait/how_it_works.shtm

Transportation Security Administration: Advanced Imaging Technology Home. (n.d.). Retrieved from http://www.tsa.gov/approach/tech/ait/index.shtm

U.S. Constitution, Amendment IV.

U.S. Government Accountability Office.

(2010, March). Aviation Security: TSA Is Increasing Procurement and Deployment of the Advanced Imaging Technology, but Challenges to This Effort and Other Areas of Aviation Security Remain (Publication No. GAO-10-484T). Retrieved from http://www.gao.gov/new.items/d10484t.pdf

U.S. v. Aukai, 497 F.3d 955 (9th Cir. 2007).

U.S. v. Davis, 482 F.2d 893 (9th Cir. 1973).

U.S. v. Hartwell, 436 F.3d 174 (3rd Cir. 2006)

Additional Resources


Iscon: http://www.isconimaging.com/

About the Author

Dillon Martinson is a Research Associate at the Center for Infrastructure Protection and Homeland Security at George Mason University School of Law. He has worked on projects and reports on homeland defense, national security, emergency response, infrastructure development, continuity of operations and continuity of government, cybersecurity, and law and policy. He has worked as a law clerk at the Department of Homeland Security Office of the General Counsel. He received a B.A. in Philosophy and a minor in Spanish from Brigham Young University and holds a J.D. from George Mason University. He is a member of the Virginia State Bar.

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