Don't Fear the Reaper: How Can Heavy Drones Be Detected, Identified and Brought Down?

Russian Defense Minister Sergey Shoigu nominated the Su-27 pilots involved in the mission to prevent a US MQ-9 Reaper drone from violating airspace near the special operation zone for state awards on Friday.

The incident has become the subject of a boisterous political debate in Washington, with enraged neocon pundits and politicians calling on the Pentagon to start shooting down Russian planes, while others pointed out that the incident took place more than 8,500 km from America’s shores, and asked how Washington would react if Moscow sent spy drones toward the US coast in the Gulf of Mexico.

The US Air Force released footage from the Reaper's encounter with the Su-27s on Thursday, showing the Russian planes approaching the drone and engaging in a fuel dump maneuver, apparently causing its engine to stall. The Pentagon called the Russian pilots’ actions "unsafe and unprofessional," and accused the Russian jets of clipping the drone, although no evidence of this was shown in the video that was released apart from a bent propeller.

However they are characterized by the Pentagon, the fuel dump maneuvers got the job done, forcing the drone to move away from restricted airspace after warnings repeated over the past year apparently failed to get the message across. The drone ended up crashing in the Black Sea, with Russian specialists dispatched to try to retrieve the wreckage (and possibly, its onboard secrets).

The General Atomics MQ-9 Reaper has been one of the US military’s main go-to all-in-one surveillance and strike drones since its introduction in 2007. The unmanned aerial vehicle (UAV) features a 20-meter wingspan, is 11 meters long, and is equipped with a 950 horsepower turboprop engine, which gives it enough power to accelerate to up to 480 km per hour (although the cruising speed is 280-310 km per hour) during flights which last between 23 and 30 hours, depending on the complement of equipment and/or weapons on board. The 2,223 kg drones can be loaded up with up to 1,700 kg of fuel and weapons, including Hellfire missiles and laser-guided bombs.

Large modern American UAVs like the Reaper and the RQ-4A Global Hawk surveillance drone were developed in the 1990s and began to be fielded in the early 2000s, well after the disappearance of the Eastern Bloc – NATO’s primary military competitor during the Cold War. Their missions in the 2000s and 2010s saw them engage in reconnaissance and strike missions mostly against small countries or militant groups, often with limited or non-existent air defenses, with a sobering 2021 report concluding that thousands of civilians, many of them children, had been killed in strikes by the so-called "precision" aerial platforms.

When matched up against militaries with modern detection capabilities, or even non-state actors with sufficient determination and mobile air defense systems, the sophisticated, $55-200 million drones can easily and quickly be turned into piles of scrap metal.

Drones like the Reaper and the Global Hawk are large, slow-moving aircraft about the size of a small manned plane. These drones and others like them have a radar cross section that’s large enough for them to be easily spotted, particularly if the adversary has sufficient radar coverage.

The US military has attempted to counter detection in a variety of ways, for example by covering drones with radar-absorbing materials or flying them at low altitudes, but for larger militaries, these forms of insurance are irrelevant, especially if the adversary has some idea of the drones’ flight patterns and mission. Russia, for example, has among the top radar capabilities in the world, inheriting a large array of ultra-long, medium, and short-range ground and air-based early warning, 3D air search radar, surveillance/acquisition, and over the horizon radar systems from the USSR, and has been building on these designs in the decades since.

Like virtually all other operational aircraft, drones can easily be detected by ordinary people, provided they have their flight transponders turned on. This is possible by using apps such as FlightRadar24, which lets users search an online database of aircraft (having access to a UAV’s callsign, registration, and serial numbers simplifies the search). Why do military drones often fly with transponders on, even if it means adversaries will have access to their flight paths? One simple answer is: to prevent in-flight incidents with other craft. During Tuesday’s incident, the Russian military pointed out that the Reaper involved was flying toward restricted airspace with its flight transponder turned off.

While Tuesday’s Su-27 fuel dump incident was a novel way of engaging a US drone, it’s not the traditional way an adversary’s UAVs are brought down. The number one cause of the loss of Reapers and Global Hawks, whether operated by the US or its NATO allies, is technical problems and bum landing attempts, which have claimed over a dozen drones between the early 2000s and now.

UAVs can also be destroyed by enemy fire, with the most high-profile incident taking place in June 2019, when an Iranian Khordad-3 road-mobile air defense battery knocked a Global Hawk out of the sky after it strayed into Iranian airspace over the Strait of Hormuz. Reapers are even more vulnerable to enemy fire, with up to five lost in Yemen and Libya between 2019 and 2022, and three more going down over Syria in apparent collision/friendly fire incidents during roughly the same period. The drones shot down over Yemen are of special interest, since the militants claiming responsibility accomplished the feats in spite of the devastating, eight-year-long blockade against the country.

Aside from fancy aerial maneuvers or direct fire, drones are vulnerable to signal loss and hacking. In late 2011, for example, Iran intercepted, hijacked, and commandeered a cutting-edge US RQ-170 Sentinel flying wing spy drone, bringing it safely to the ground in the country’s northeast. Iran studied the UAV and created a reverse-engineered domestic version. An Iranian company responded to a US request to have the drone returned by promising to send President Barack Obama a miniature plastic toy version as a present.

Most contemporary military drones are equipped with anti-hacking systems designed to avoid a repeat of the embarrassing 2011 incident, including encrypted communication systems between itself and its remote operators. However, even in the case of major military power like the US, the 2011 Iran incident shows that there is no guarantee that a drone operating outside friendly airspace cannot be intercepted and brought down.