In 2006, a conspiracy to carry liquid explosives on flights from London to the US and Canada prompted the Transportation Security Administration to impose a 3-ounce limit on all containers of liquid and gel in hand luggage.
This led to the now-famous and widely maligned 3-1-1 carry-on rule: each passenger puts a 3-ounce container in a 1-quart bag. The 3-1-1 rule has been in place for 17 years. Since then, airport security has advanced both strategically and technologically. The most significant strategic change was the introduction in 2011 of the risk-based PreCheck system, which better informs the TSA about travelers and allows them to quickly clear airport security checkpoints.
TSA is currently deploying computed tomography (CT) screening devices that can provide a more accurate 3D view of baggage contents.
The UK has decided not to and is taking steps to phase out the rule. London City Airport, the first in the UK to waive the rule, is scanning hand luggage with CT scanning equipment that can more accurately check liquid containers up to two liters, or about half a gallon. Liquid explosives have a different density than water and can be detected using CT scanning equipment.
For now, the UK government says there have been no safety incidents with CT scan equipment. It’s a ridiculous way to measure success.
If any terrorist group wants liquid explosives through airport security checkpoints, it is best to wait until other UK airports step in and other countries follow suit by allowing large containers of liquids in hand luggage. A massive attack could be planned in the hope that some kind of liquid explosives would break through the security system, causing widespread chaos and destruction.
Advances in airport security are needed, and what was needed 10 or 20 years ago may no longer be needed to keep the aviation system safe.
The good news is that almost all travelers pose no danger to the aviation system. Terrorist threats are like finding a needle in a haystack. The likelihood of security breaches due to policy changes in the short term is extremely low.
One downside to the UK’s decision is that not all passengers are created equal in terms of safety. Most of them are really good. One would even rightly suggest that on any given day all travelers are benevolent. However, policies should be in place to manage not only most days, but also unusual days. CT screening equipment provides layers of reinforcement to reduce risk and provide the necessary protection.
However, CT screening devices are not without limitations. They can have false positives that can slow down the flow of people at checkpoints, or false positives that can lead to security breaches if passengers get it wrong. In the United States, while the 3-1-1 policy is still in place, the speed of travelers passing through security lines has slowed as Transportation Security Administration (TSA) officials adapt to the new CT equipment.
The UK does not act blindly. It also actively promotes biometric facial recognition as a means of verifying a traveler’s identity. As such, restrictions on items such as liquids and gels can be relaxed if travelers are aware of their security authorities.
Implementing similar policy changes at US airports will require the TSA to learn more about passengers. This can be achieved in two ways.
One of these is the free PreCheck offer to any traveler who wishes to complete the required background checks. Another approach could be to increase the use of biometric authentication such as facial recognition, which would provide similar risk reduction benefits.
Such passengers are allowed to check in baggage according to the 3-1-1 scheme. Passengers who are still unaware of the TSA will still be subject to this rule.
Some may argue that known TSA travelers can still carry liquid explosives through security checkpoints and cause injury. This highlights why a rigorous process of verifying whether they are a known traveler or using biometric information should be the key to relaxing the 3-1-1 rule, since the risks associated with such people are extremely low. The added layer of security provided by CT imaging equipment will reduce the residual risk.
In the short term, no. However, the lesson learned is that responses to past threats need to be reviewed periodically.
Compliance with the 3-1-1 rule would require the TSA to be aware of more riders. The biggest hurdle to using facial recognition to achieve this goal is privacy concerns, which have been pointed out by at least five senators in hopes of preventing its spread. If these senators are successful, it is unlikely that the 3-1-1 rule will be lifted for all passengers.
Changes in UK policy are pushing other countries to review their liquidity policies. The question is not whether a new policy is needed, but when and for whom.
Sheldon H. Jacobson is Professor of Computer Science at the University of Illinois at Urbana-Champaign.
Post time: Aug-04-2023
