Are airport perimeter security breaches a threat to air travelers?

Last week, a person scaled the perimeter fence at Chicago Midway airport and gained access to the airport’s tarmac, creating a potential security threat on the secure side of the airport.   

How often do perimeter security breaches occur, and do they pose a threat to air travelers? 

Perimeter security breaches are not common, although they do occur frequently enough to be reported in the media. In 2021, a person cut through a perimeter fence at Los Angeles International with the intent to board an airplane that was being serviced. In 2018, a person scaled the perimeter fence at Atlanta Hartsfield, gaining access to an active taxiway In 2015, the Associated Press found over 260 perimeter security breaches dating back to 2004.

The most effective airport security strategies use multiple layers, an approach employed by the Transportation Security Administration (TSA). For perimeter security, these layers include barbed wire fences, surveillance cameras, motion detection technologies and patrols. Given the expansive physical footprint of large major metropolitan area airports, protecting miles of perimeter is challenging.  

When a person breaches security through the airport perimeter, they gain access to secure areas where airplanes are parked, as well as active taxiways where airplanes containing passengers may be in transit for takeoff or landing. Such perpetrators may also carry with them weapons, further adding to the risk of damage and harm. 

However, outside of the terminal area, airports offer few places for such perpetrators to hide. As a result, additional layers of surveillance inside the perimeter results in any such security breaches being detected before harm and damage can be inflicted. 

The good news is that the number of airport perimeter security breaches appear to have dropped off considerably since 2015, based on fewer incidences being reported in the media. When they do occur, the people involved are quickly intercepted before any damage and harm occurs. 

In an ideal world with unlimited resources, every threat should be stopped at the earliest possible time. In the real world, with limited resources, tradeoffs must be made to balance the risks and benefits of allocating scarce resources. That means comparing the risk posed by airport perimeter breaches versus the risk of an air traveler getting onto an airplane with intent to cause harm on a flight.  

Indeed, the biggest challenge for the TSA is likely assessing the intent of every traveler who enters the air system. Without the ability to read people’s minds and their intentions, the next best thing is to prevent items that could be used to inflict harm on a flight, such as firearms, knives and explosive devices, all of which are prohibited by the TSA. 

Ask yourself the following question: which passenger is riskier to the air system: 1) a passenger with seemingly no malicious intent carrying a weapon onto an airplane, or 2) a passenger with apparent malicious intent but no weapon on a flight? I would argue that the person with malicious intent poses a far greater threat to the air system, even if they do not board a flight with a weapon.   

TSA PreCheck serves as a surrogate for measuring intent. That is why physical screening at airports is expedited for PreCheck vetted passengers. The voluntary background check that PreCheck passengers undergo makes them a known traveler with low risk. In my view, even if they did happen to carry a prohibited items onto an airplane, with benign intent, their risk to the air system is likely negligible.       

So, are perimeter security breaches a risk for air travelers? The simple answer is yes. Anytime a person breaches an airport perimeter, they create confusion and chaos, disrupting airport operations. During such events, all air travelers are at an elevated level of risk.   

However, the greater risk to the air system are the passengers themselves.    

The air system is most secure when passengers voluntarily provide as much information about themselves to the TSA. The more passengers who are willing to do so, such as by enrolling in TSA PreCheck, the more secure the air system is for all.  

Sheldon H. Jacobson, Ph.D., is a founder professor of Computer Science at the University of Illinois at Urbana-Champaign. He applies his expertise in data-driven risk-based decision-making to evaluate and inform public policy. He has researched aviation security systems since 1995, providing the technical justification for TSA PreCheck.