For the second time in less than a month, flights at a major London airport have been halted by drone activity. On Monday evening, departures from Heathrow Airport were stopped for about an hour after a drone sighting nearby with the British military investigating the situation.
But at a time when the number of drones—hobbyist and commercial—will only increase, is there anything airports and governments can do to safeguard against delays, and, in the worst circumstances, fatal collisions?
Tiny Drone, Big Threat
It’s no secret that a collision between an airliner and a drone could be catastrophic. Even though it’s small, these “mechanical geese from hell” pose big threats to a plane’s exterior and its engines.
Yesterday’s disruption at Heathrow has been minor compared to the holiday mess at Gatwick Airport, which shut down after an airport security officer spotted two drones flying over a perimeter road. Over 140,000 passengers had their flights diverted or delayed. Airport operations at Gatwick did not resume until 36 hours after the original incident.
Geofencing restrictions built into consumer drones are supposed to stop them from operating in prohibited areas but those safety measures can easily be hacked. New UK laws prohibiting drone use near airports may stop hobbyists, but are clearly not enough to stop malicious users, such as criminals, terrorists, or activists bent on stopping flights.
That leaves the use of force. The “military capability” brought in at Gatwick was withdrawn on January 3 and is now at Heathrow. The Ministry of Defence refuses to comment exactly what they are using, but we can gather a pretty good idea of what it is and what it does.
There are currently six different ways to take down a drone, and some more plausible than others.
Detect, Identify, and Jam
Small drones are elusive. Despite 93 credible sightings by witnesses at Gatwick Airport, there was no good video of the drone in action, and drones are just as difficult to spot on radar. Radar to spot and track aircraft is designed to filter out small, slow objects, which were previously most likely to be birds, so special sensors are needed for drones.
According to Aviation Week Magazine, the system used at Gatwick was the $6 million Anti-UAV [Unmanned Aerial Vehicle] Defence System or AUDS. This combines a radar sensor from Blighter, a Hawkeye video tracker and thermal imager which can track and classify a drone, and a radio jammer from Enterprise Control Systems.
Jammers work by interfering with communications between the operator and the drone. This is fairly easy with commercial drones, which operate on known wavelengths and have no resistance to interference. When a drone loses the radio link, it will attempt to fly back towards the operator to re-establish a connection. If GPS navigation is also jammed, it will usually land on the spot.
There are many similar drone detection and jamming systems. According to The Times of Israel, the British used the Drone Dome system from Israeli company Rafael at Gatwick, another one combining specialist sensors and jammers. This is certainly possible given that the UK purchased a system earlier in 2018.
However, this type of defense works only with consumer drones, which often rely on radio signals. More advanced drones can work on their own; for example, the new Skyraider from Aeryon has a “Dark Mode” for covert operations, flying autonomously with no operator link, while DARPA’s Collaborative Operations in Denied Environment shows how whole swarms of drones can work together when both communications and GPS are jammed.
And this capability is only going to spread.
Shoot ‘Em Down
Police considered trying to shoot down drones at Gatwick, but even that is not as easy as it sounds. While drones have been knocked down with thrown sticks, beer bottles, or by shotgun-wielding neighbors, these are usually slow or stationary drones hovering at short distance. Police at Gatwick were pictured armed with shotguns, which present less of a safety hazard than rifles but are only effective at close range.
At an altitude of several hundred feet, and moving at 30 mph, a drone is an extremely challenging target. The U.S. Army’s guidance on tackling small, low, slow drones advises that rather than individual soldiers trying to shoot at the drone, the entire platoon should fire their rifles and machine guns at a fixed point in the sky in the drone’s flight path so it runs into a wall of lead.
However, every bullet has to land somewhere, and bullets can be dangerous more than a mile away. Massed firing into the sky in densely populated southern England would be likely to end up with unacceptable collateral damage. Even one broken window would draw unfavorable media attention.
Call In R2-D2
Maybe something more advanced than manually aimed bullets is needed.
The Phalanx CIWS fitted to U.S. warships is a computer-controlled, radar-guided cannon with an awesome rate of fire. Affectionately known as R2-D2 (and “the Dalek” to UK Royal Navy crews), it spits out 70 20mm rounds a second and can shoot down sea-skimming missiles at the last second before they reach a ship. A modified version, C-RAM, defends U.S. bases from rockets and mortar rounds.
CIWS looks ideal for taking out small drones with shells designed to “explode at a certain altitude so as to reduce injuries on the ground.” But any duds would leave an area littered with unexploded ordnance, something that’s happened to London before. During World War II, falling anti-aircraft shells sometimes did more damage than the bombers they were supposed to shoot down.
For the meantime though, these systems are simply not built to deal with small, slow threats at low levels. Rockets and mortar rounds come in on a high trajectory where they show up well on radar, whereas drones can stay close to the ground. Phalanx would need to be integrated with a new radar/sensor system to cope with the threat, and protecting a major airport like Gatwick would be an expensive proposition.
Tangled Up in Nets
Nets are safer than bullets or missiles with no risk of collateral damage to the surrounding area. Skywall made by UK company Liteye is a bazooka-like device, which fires a net to entangle a drone and parachute it safely to the ground. There is no danger to anyone underneath and the drone is captured intact for forensic analysis.
Other net projectiles range from Skynet 12-gauge shotgun cartridges to 40mm cannon rounds. But high-velocity rounds are dangerous projectiles. Skywall is launched with compressed air, which ensures that it is safe but means that range is limited to about a hundred meters, which would have been of little use to security personnel at Gatwick.
Getting a Bit Sci-Fi
On its surface, lasers look like the ideal way to counter drone weapons. They are precise enough to hit small, agile targets a mile away, and there is no risk to people or property on the ground.
Israeli aerospace outfit Rafael, who make the Drone Dome system allegedly deployed at Gatwick, can also supply a laser “hard kill” anti-drone module. There are a vast number of other counter-drone lasers jostling for room in the marketplace, from the U.S. Army’s own version, to systems from makers like Raytheon and Lockheed Martin and European firms BAE Systems and Rheinmetall. Not to mention similar systems in China and Russia.
Lasers have been shooting down drones on test range since 1973, but have not yet been used in action because of a key issue known as “dwell time.” Rather than being instantaneous like a bullet, the beam has to stay focused on the drone for a period of time to melt or burn it enough to bring it down. Drones in tests fly in convenient straight lines, an unlikely path for a real target.
Military lasers also work on specific, known wavelengths, so operators could coat their drones in protective material to reflect that specific frequency and degrade the laser’s effectiveness.
Fighting Fire With Fire
In the end, the best way to bring down a drone may be with another drone.
An event known as DroneClash, organized in 2018 by Delft University of Technology, challenges developers and engineers to find creative ways to counter threat drones without any risk to bystanders. In last year’s competition, teams armed their drones with entangling devices and dart guns or reinforced them for ramming. Dogfighting drones are a cheap, long-range solution which can be directed with high precision.
The military has also done something similar. In June 2018, the U.S. Marine Corps fielded a mobile defense system called GBAD with an array of sensors, jammers, and missiles, along with a pod of interceptor drones. These are based on Raytheon’s Coyote drone and are armed with high-explosive warheads. Unlike missiles, the interceptor drones should not present a hazard if they fail to find a target and may even be reusable.
No Easy Solution
The motives of the drone operators at Gatwick and Heathrow are not known, but another drone incident looks like a near certainty. None of the existing solutions is likely to work on its own. In the future, airports are likely to rely on a variety of drone detection and tracking sensors, backed up by jammers and other systems such as interceptor drones.
Cost will be an issue. While big airports like Gatwick and Heathrow may be able to afford several million for drone protection, smaller operators will not have that luxury, simply shifting the problem to the places that are less able to deal with it.
Any failure is likely to lead to another shutdown, and at worst, a malicious drone could bring disaster.