Are We Safer – Part 7: Perimeter Security

behind the fence


In 2012, the issue of perimeter security made headlines numerous times. From a jet-skier swimming to shore and accessing the ramp at JFK, to a drunk driver slamming through the perimeter gates at Phoenix-Sky Harbor, to a former airline pilot jumping the fence at St. George’s, Utah where he proceeded to access a regional jet and crashed it into a building on the ramp – it seemed hardly a week went by when there wasn’t another news story about airport perimeter security.

Perimeter security is closely associated with the access control system, but is generally considered to be the perimeter fencing of the airfield. Typically, there is a 7-foot chain length fence topped with 3-strands of barbed wire along the top. In some cases, for airports that border bodies of water, often times a fence is not necessary as the water serves as an approved barrier. Plus, there are safety issues if the runway is too close to the water – putting a fence in between the runway and water could either put the fence into the Safety Area (an area around the runway that is supposed to be free of unnecessary objects), or fencing may complicate an aircraft rescue attempt if a plane goes off the runway, through the fencing and into the water.

I think when many people hear about perimeter security intrusions they have the mistaken belief that the perimeter of the airport is supposed to be some sort of impenetrable barrier, on a par with a maximum-security prison. I’ve been to Israel and seen the multiple layers of perimeter fencing at Ben Gurion, which has 3 different fences, including a delaying fence (common at prisons) and a full perimeter intrusion detection system (PIDS). But, Israel also has different and more frequent threats which justifies the higher security measures.

Airport perimeter security began in the late 60s and early 70s, but mostly served to prevent people from inadvertently accessing the airfield and getting hurt, or causing a safety issue for an aircraft. As airport security became more of an issue in the 1980s, fencing became a standard part of the security at most commercial service airports, and at many busy general aviation airports. The standards have largely remained unchanged ever since, even after 9/11.

The Aviation and Transportation Security Act of 2001 did not require airport operators to make changes in their perimeter security, but several airport operators are seeing the need to better protect the perimeter, such as more frequent security or law enforcement officer patrols, maintaining clear zones (i.e. no parking or anything that could assist an individual in scaling the fence) within 3-feet to 10-feet of the fence, and in some cases airports have installed perimeter intrusion detection systems.

While it is terrible press and there are safety issues when someone gets onto the airfield, we have to look at what types of attacks could be carried out that the perimeter is supposed to prevent or mitigate before deciding if the existing controls are adequate. Essentially, there are three key risks:

  1. Accessing the airfield by jumping the fence, then placing an improvised explosive device on an aircraft or boarding an aircraft to hijack it.
  2. Crashing the gate or fence with a vehicle and attempting to ram it into an aircraft. A variant on this is to fill the vehicle with explosives.
  3. Launching or firing a stand-off weapon, such as an aerial IED (placed along the final approach path and designed to detonate as the pilot approaches it or flies over it, rocket-propelled grenade attacks (remember Blackhawk Down?), surface-to-air missile shot, otherwise known as a MANPAD (Manned Portable Aerial Defense System).

There have been numerous hijackings over the course of history where the hijackers dressed as everything from security guards to customs agents and bluffed their way through an airport perimeter gate. Good gate controls and well-trained security officers are the key to prevention here.

Whenever someone jumps the fence during the day, it’s likely that the air traffic control tower will see them coming across the airfield, unless its in an area shielded from ATC’s view by buildings or equipment. While controllers aren’t security personnel, from a safety perspective they will report the intrusion to airport police. Plus, individuals walking around on the airfield are typically in the Security Identification Display Area (SIDA) and are subject to challenge by other airport employees (it’s a responsibility of having the SIDA badge) if they see someone not displaying a badge. So there are some extra security layers here besides just the fence.

At night, it can be difficult to detect an intruder jumping over the fence or swimming to shore unless there is a PIDS system in place. It is possible that an individual can jump the fence (it isn’t that difficult – it’s something every Marine Corps boot learns about week 1 in training), then access an aircraft to potentially place a bomb on board. However, if that person approaches the aircraft while its being loaded with cargo and bags, ramp workers are going to wonder who this person is and why they are there. Even if the person has a visually valid identification badge (i.e. the expiration date has not been reached) everyone will still wonder who the “new guy,” is that just showed up to load bags.

An individual could try to place the bomb on board an unattended aircraft but the doors and access panels are supposed to be secured when the aircraft is unattended and any attempt to place the bomb externally would likely be caught by the pilot or maintenance chief during the pre-flight procedure.

There is also the threat that an individual who knows how to fly (i.e. the Barefoot Bandit, or the Skywest pilot) can hop the fence at an airport and steal a plane, to possibly turn it into a weapon of mass destruction. In fact, the show Airplane Repo seems to constantly demonstrate how easy it is to access certain general aviation airports and fly off without the owner even knowing about it. It is a possibility that a bad guy and a copy of Microsoft Flight Simulator can do the same thing.

Whenever someone crashes the gate, the airport immediately shuts down and air traffic control stops all air traffic so the chances of a car-vehicle collision are reduced. If a car hits an aircraft, which has happened numerous times in the form of an accident not an intentional act, the car and the vehicle are rendered useless but not much else occurs. There is a possibility the car or truck could be filled with explosives, but if that’s the case there are better targets at the airport that are easier to access, like the terminal building. Plus, the destructive power of bomb on going off on a plane at altitude (in a pressurized environment), is far greater than if it goes off on the ground – in other words, you’re not getting a lot of bang for your buck here.

Then we have the stand-off attacks. These are not so much perimeter intrusion issues as a rocket-propelled grenade, an aerial IED or a surface-to-air missile can all be fired from off-airport.

According to Defense Tech, insurgents in Iraq, have placed aerial IEDs along known flight paths, then trigger them when American helicopters come along just above the rooftops. The devices shoot 50 feet into the air, and a proximity fuze touches off a warhead that sprays metal fragments, said Brig. Gen. Edward Sinclair, commander of the Army’s Aviation Center at Fort Rucker, Ala (DefenseTech). While we have not seen this type of attack on civil aviation it is certainly a possibility. Flight paths and altitudes into and out of U.S. airports are well established and published in numerous open source documents.

RPG’s or rocket-propelled grenades, like the kind that brought down two helicopters in Somalia in the infamous “Blackhawk Down,” incident are also a threat to civil aviation. While most are predominately an unguided line-of-sight weapon, the advantage a terrorist has is that commercial aircraft are not executing evasive maneuvers while on approach or takeoff, making them easier to hit. Then there are the surface-to-air missiles. While most shoulder-fired missiles are heat-seeking (few infrared; most radar homing and wire guided are vehicle or boat mounted) and they have been used with limited effectiveness a few times throughout history, their proliferation throughout the world still makes them a credible threat.

For all three types of attacks, aerial IED, RPG and missile, risk assessments of the best areas from which to fire these weapons and adding the identified sites to those areas for patrol by law enforcement and security personnel, can be an effective defense. There are a few anti-missile defense systems in development for commercial aircraft but they are expensive systems and presently, the risk doesn’t seem to justify the cost.

An airport operator that wants to increase perimeter security can take one of several actions:

  • Increase airfield patrols by airport security, law enforcement and operations personnel
  • Install perimeter intrusion detection systems to detect when someone is coming over the fence (motion sensors, etc.)
  • Make better use of or upgrade their CCTV technologies to include smart-video analytics tied into an intrusion alarm system, and install night-vision capabilities on CCTV cameras
  • Eventually, it may make sense and the risk may justify it, but the use of Unmanned Ground Vehicles (similar to UAV’s but on the ground – think: Robot) to conduct airfield patrols using a combination of CCTV, sensors and the ability to drive relatively unseen (as compared to a cop car or security vehicle) around the field

Whether we are safer in the area of perimeter security remains to be seen. While the risks so far are few, the consequences of some of the risks could be catastrophic. There hasn’t been a regulatory mandate to “fix” perimeter security and TSA says that it’s an airport function, but just with the publicity and with security audits identifying many vulnerabilities, we are seeing more and more airports take perimeter security into consideration. I would also encourage you to review Tom Clancy’s novel Against All Enemies, which runs the scenario of a surface-to-air missile attack within the U.S. on commercial aircraft, keeping in mind that Clancy’s novel Debt of Honor, published in 1994, was about a commercial jet crashing into the U.S. Capitol.

I expect in the future we will see more perimeter intrusions and while not much has changed in how we protect the perimeter, so far, the threat hasn’t changed much either. . . yet. 



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