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Is the U.S. About to Change Its Liquid Rule on Flights?

The U.K. has started phasing it out. Is the U.S. next?

The queues at airport security checks can be frustrating. The experience itself isn’t pleasant either—you’re finding trays, reading signs on what needs to be removed (every airport may have different rules), and rushing to make sure you’re not holding up others.

Now imagine gliding through security after just placing your carry-on on the scanner belt—no need to take anything out. That might become a reality soon, at least for passengers in the U.K.

In March, a small airport in the U.K. became the first to ditch the 100ml liquid rule. At Teesside Airport, passengers are now allowed to take up to two liters of liquid in their carry-on and don’t have to take out the clear bag with liquids and gels. Laptops and electronics can also stay in carry-on bags before going into the scanner.

This change comes after the government gave a deadline to U.K. airports to install high-tech 3D scanners by June 2024. Mark Harper, Secretary of State for Transport, emphasized that the new technology will reduce wait times and improve passenger experience, and also detect potential threats.

The London City Airport has also switched to Computed Tomography (CT) scanners that take 3D images of bags. “The level of processing now through the X-ray is even more secure than it was previously and the machine has the ability to differentiate between a non-dangerous and a dangerous liquid,” chief operating officer Alison FitzGerald told the BBC.

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The Origins of 3-1-1

The Transportation Security Administration (TSA) 3-1-1 rule is 3.4 ounces (or 100ml) per item in one quart-sized bag per customer. You are allowed to take liquids, gels, and creams in your carry-on luggage if the items are less than 100ml and placed in a clear bag. You have to remove this clear bag from your carry-on when you place it in the scanner. The exemptions to this rule are baby food/formula and medications, but these have to be declared to security.

It’s not an arbitrary rule—it’s a major security measure.

In 2006, the U.K. thwarted a terrorist plot to detonate bombs on flights from the country to the U.S. The bombers were planning to take hydrogen peroxide (among other things) on transatlantic flights in their carry-ons as soft drinks. The scanners wouldn’t have been able to detect liquid explosives, and the whole plot was based on what couldn’t be screened. It was revealed that 10 flights were targeted, but a massive surveillance operation by the British Metropolitan Police and MI5 (British secret service) arrested perpetrators and saved hundreds of lives.

In the days that followed, airport security became chaotic and liquids were banned from carry-ons. Later, the 3-1-1 rule was adopted after tests found that these quantities couldn’t create an explosive. Kip Hawley, former TSA director, spoke to The New York Times in 2007 about the unpopular rule. “Separate three-ounce containers limited in number to what will fit inside a single one-quart bag do not have ‘enough critical diameter’ to blow up an aircraft.”

Currently, airport screening for carry-on baggage depends on 2D images to understand what is inside. Vance Hilderman, aviation expert and CEO of AFuzion, explains that traditional scanners can’t discern potential explosives from toothpaste or jam. “It was felt that super-enriched explosive material was very hard to obtain and detonate, so the 3-ounce rule was implemented in response to prior threats.” 

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Advances in Tech

Computed Tomography (CT) is used in the medical field to scan a patient’s body. The same technology is being deployed at airport checkpoints. The TSA says, “The CT scanners apply sophisticated algorithms and create 3-D rotatable images to help operators detect explosives and prohibited items. TSA officers can then view and rotate the image on three axes to analyze and identify any threat items that may be in a passenger’s carry-on baggage.”

The CT technology has been used for years to scan checked-in baggage. Now it’s being retrofitted for airport security checkpoints to check for threats in carry-ons. 

There are many other destinations around the world that have deployed this technology to make the process smoother. Airports in Tokyo, Amsterdam, Rome, and Stockholm are using CT scanners, so passengers don’t need to take out liquids and electronics from their bags. 

In the U.S., trials have been ongoing, but the 3-1-1 liquid rule remains in place. Only those with TSA Pre-Check can pass through security while keeping their liquids and electronics in their bag and belts.

According to the TSA, there are 634 CT units installed in airports across the country and the federal agency has invested $1.3 billion to procure 426 base, 359 mid-size, and 429 full-size units. TSA Administrator David Pekoske said in the statement, “These CT units represent sophisticated technology that helps our professional, dedicated, and highly skilled workforce detect new and evolving threats to improve aviation security. Deploying these units across our security checkpoints as expeditiously as possible will also improve checkpoint efficiency and the passenger experience.”

Hilderman adds that explosive technology has also evolved and theoretically, smaller amounts of liquid explosives can also do substantial damage. “The threat is real, though small: this is why TSA is additionally focusing upon improving passenger identification and profiling [through Clear and TSA Pre-Check].”

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It Might Not Happen in the U.S. Soon

Although efforts are underway in Europe to replace 2D scanning with CT, it will still take a long time for the U.S. to scrap its 3-1-1 rule. 

When Fodor’s contacted the TSA, they said, “Computed Tomography technology produces 3D images that can be rotated and combined with advanced detection algorithms to produce a substantial improvement in security screening. While we have them deployed at more checkpoints, we are years away from announcing a change to the current liquids rule.”

Hilderman is on the same page. He says that the FAA and the TSA will see how it goes in the U.K. and other countries and delay any decision on the liquid rules. “It will be at least three to five years until the U.S. follows other countries such as the U.K. in relaxing the 3-1-1 rule.  This is because the U.S. has vastly more airports, travelers, and equipment to upgrade.” 

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