Drone Incursions and Anti-Drone Measures

Drones have been flying in and over places they shouldn't: nuclear power plants, airports, and MLB games.
Marcia Wendorf

At 8:50 p.m. on September 29, 2019, security guards at Arizona's Palo Verde Nuclear Generating Station noticed something unusual. A half dozen mysterious drones were flying over the facility's perimeter fence.

Housing three nuclear reactors, Palo Verde is the largest power plant by net generation in the U.S., supplying electricity to an area bounded by Texas on the east and California on the west. The plant is located just 50 miles (80 km) west of the city of Phoenix whose metropolitan area is home to almost 5 million people.

The security guards described the drones as being about two feet (60 cm) in diameter, flying at an altitude of between 200 and 300 feet (60 and 90 m), having red and white lights, and having employed their spotlights as they approached the plant.


The drones flew over a series of gates, arriving at the area surrounding the reactors' concrete domes. The guards watched as the drones remained there for nearly an hour before flying off. Then, to add insult to injury, the next night at 8:51 p.m., four drones returned and stayed for an hour, only this time, they didn't need their spotlights to find their way.

Because drones are operated by remote control, it's hard to determine who was operating the drones, or what their intentions were. However, the drone flights were definitely illegal because Arizona has a law that prohibits drones from flying 500 feet (152 m) horizontally or 250 feet (76 m) vertically from any critical infrastructure. In this case, "critical infrastructure" must certainly include a nuclear power plant.

A couple of clues

Most consumer drones have a battery life of about half an hour, while the drones at Palo Verde appeared to stay longer. A vice president of site services at Palo Verde, Mike McLaughlin, told AZCentral, which is the digital presence of The Arizona Republic newspaper, that given the darkness, it was difficult to tell the number of drones, or their size and altitude.

McLaughlin also told the website that there was only a minimal chance that the drones could damage the steel- and concrete-reinforced containment domes, or that they could penetrate the buildings that house nuclear material.

Arizona's Palo Verde nuclear plant
Arizona's Palo Verde nuclear plant, Source: Dept. of Emergency and Military Affairs

This is perhaps why the security guards didn't open fire on the drones. McLaughlin told AZCentral, "...there is an amount of risk in trying to shoot something out of the sky. There are families and homes around. I don’t want to be the station that unilaterally takes action against drones."

Palo Verde plant officials were alarmed enough to alert the Maricopa County Sheriff's Office, the Federal Bureau of Investigation (FBI), the Nuclear Regulatory Commission (NRC), the Federal Aviation Administration (FAA), and the Department of Homeland Security (DHS).

The NRC deemed the fact that there were two nights of incursions, and the drones performed various suspicious maneuvers, as threatening, and they began coordinating with the FBI's Weapons of Mass Destruction Directorate, thus showing how seriously the NRC took the incident.

The Palo Verde incidents are not the first time drones have flown over nuclear power plants. NRC documents made public by TheWarZone show that there were 42 drone incidents over nuclear power plants during a three-year period, including drone overflights that occurred at the Limerick Generating Station in Pennsylvania early in 2019.

While the airspace above nuclear power plants is not currently restricted, an NRC spokesperson told AZCentral that the Department of Energy is working with the FAA to designate that airspace as restricted.

MLB game - August 5, 2020

On Tuesday, August 5, 2020, a Major League Baseball (MLB) game between the Minneapolis Twins and the Pittsburgh Pirates had to be delayed for nine minutes due to a drone flying over Minneapolis's Target Field.

It's possible that whoever the drone operator was, he or she was a Pittsburgh fan because the drone appeared at the top of the fifth inning, with the Twins up 5 to 1, and their pitcher, Jose Berrios, was in the middle of a hot streak.

While the security guards at Palo Verde refrained from attacking the drones, the baseball players had no such compunction. Pitchers from both bullpens threw baseballs at the drone, without hitting it.

By Federal Aviation Administration rules, drones and other "unmanned aircraft systems" cannot fly closer than three nautical miles (5.5 km) from any MLB stadium, beginning one hour before the start of a game, and ending one hour after the end of a game.

Drones are also prohibited from flying over National Football League (NFL) games, some NCAA football games, and auto racing events.

In December 2018, drone sightings at London's Gatwick Airport forced that facility to close for three days, affecting 120,000 people. To date, no one has been arrested. In 2017, at Quebec City, Canada, a drone hit the wing of a commercial airplane. Luckily, no one was hurt.

In May 2017, a drone flew over a Padres-Diamondbacks game in San Diego, California, and it crashed into fans in the stands. Instead of taking home a baseball as a souvenir, one fan took home a drone.

Anti-drone measures

The FAA maintains a list of unmanned aircraft (UAS) incursions that is available to be viewed or downloaded. Fines levied by the FAA for drone incursions range from $1,100 and $2,200.

Palo Verde announced that is planning to use an anti-drone system made by Chandler, Arizona's Aerial Armor company. Their system can track drones and determine from where they were launched within a 13-mile-wide (20-km-wide) radius.

San Francisco-based firm, Dedrone, installs sensors on rooftops and inspects radio frequencies to detect drones. The Dedrone system is currently installed at airports, shipping terminals, air force bases, sporting events, and prisons.

The Dutch firm Delft Dynamics’ DroneCatcher is a drone that goes after other drones. It can lock onto an enemy UAV in the air, then catch it in a net from up to 21 yards (20 m) away.

Two of the most common radio frequencies used by quadcopters are 2.4 GHz for connecting a ground transmitter to a drone, and 5.8 GHz. However, 2.4 GHz is also used by Wi-Fi, older cordless phones, garage door openers, and baby monitors. If operators fly a drone over a densely populated area, this can result in their losing contact with the drone.

Some anti-drone systems scan for those two radio frequencies, and other systems actually jam those frequencies, however, they can only be legally used by the appropriate agencies.

The British-based company SkyWall uses air-powered cannons to launch nets at drones to bring them down. However, the most inventive anti-drone measure has got to be the one from Amsterdam's Guard from Above. That company uses trained eagles to snatch drones from the sky and deposit them on the ground.

No matter what measures are used against them, it's clear that drone incursions are going to continue in the future, and that clever solutions are going to be needed in order to thwart them.

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