The increasing popularity and widespread availability of drones is causing concern for those within the aviation industry, both from safety and security points of view. Collisions with aircraft are increasing in frequency, and terrorist organisations are already exploiting the access opportunities and anonymity that they offer. Clayton Simmons explores these issues and discusses the large counter-drone industry which has subsequently developed.
The ease of obtaining drones or unmanned aerial vehicles (UAVs) has bred a vast associated industry, and we are seeing widespread use by civilians, the military and non-state actors. Many industries are now using drones owing to their ease of use, availability, cost savings and their ability to perform dangerous tasks without risking lives. The military are able to use drones for surveillance and attack purposes. Non-state actors have also found similar uses. The roles that drones can perform are only limited by imagination.
However, drones are becoming an increasing threat to aviation. Threats could range from an uninformed (or ignorant) amateur operator breaching state rules to a terror organisation intent on inflicting mass damage and casualties. Fortunately, the latter has not occurred, however, there has been one known attack on a military airfield utilising drones but no known deliberate attacks on an aircraft. Drones are easy to obtain and easy to use. At the time of writing, there are over 3,500 drones listed for sale on eBay alone. They are also extremely easy to construct from either scratch or in kit-form.
Aircraft and Drone Collisions
At least seven collisions between aircraft and drones have been reported worldwide.1 Three of these collisions resulted in no damage whereas one in the United States involving a sports biplane resulted in a crushed wing. A Grob G 109B motor glider had its wing broken in Germany resulting in two fatalities. As recently as last October, a Beechcraft King Air struck a drone in Canada, fortunately resulting in only minor damage.2
“…observed by the flight crew of a Boeing 737 passing the right-hand wing whilst descending through 2,000 ft on approach into Adelaide…”
There was also another collision last November with a Boeing 737 on final approach into Buenos Aires Jorge Newberry Airport; there was some surface damage caused to the aircraft on the front left-hand side of the fuselage, adjacent to the captain’s position which resulted in the aircraft being taken out of service for repairs. The incident occurred in a restricted area where drones are forbidden to fly.
A drone was also observed by the flight crew of a Boeing 737 passing the right-hand wing whilst descending through 2,000 ft on approach into Adelaide, Australia. In the United Kingdom, in the second half of 2017, there were 35 drone-related incidents reported to the authorities. These occurred up to an altitude of 12,000ft. Some consumer level drones have a service ceiling of 20,000ft although battery limitations will generally preclude this altitude from being reached.
It has become an extremely serious issue in the United States with the FAA receiving 100 reports per month, 60% occurring within 8 km of an airport with eleven events involving aircraft having to be manoeuvred out of the way of a drone, including one where a Cessna 182 had to enter into a 50-degree bank angle in order to avoid a collision. A normal bank angle is up to 30 degrees. The Centre for the Study of the Drone at Bard College in New York State, US has analysed statistics and deduced that over 90% of incidents involving drones and aircraft have occurred above 400ft – the maximum allowable altitude for drones in the US – with the majority occurring within five miles of an airport, which is prohibited airspace for drones.3
The Consequences of a Collision with a Drone
What are the consequences of an aircraft impacting a drone in flight? That will vary depending on where the point of impact is, and the size and speed of the aircraft. BALPA, in conjunction with the Military Aviation Authority and Department for Transport in the United Kingdom, recently conducted some research into mid-air collisions between drones and aircraft. The research was computer simulated and conducted in a laboratory.
“…the FAA receives 100 reports per month, 60% occurring within 8 km of an airport with eleven events involving aircraft having to be manoeuvred out of the way of a drone”
According to the aforementioned study, an impact with the windscreen of an aircraft may result in catastrophic damage to an aircraft depending on the size of the drone and the speed and type of aircraft. Real conditions could not be simulated so it is not known what effect aircraft pressurisation of the fuselage would have and if this would help in mitigating the impact forces in any form. Windscreens on transport aircraft have a design requirement to be strong enough to withstand impact with a 4lb bird at cruise speed. A bird though, is mostly comprised of soft tissue and fluid and largely disintegrates on impact, whereas a drone is manufactured out of solid plastic and has metal engines that do not have the disintegration capacity of a bird. It was noted in the research that light aircraft and helicopters that do not have bird strike certified windscreens fare much worse than those aircraft with bird strike certified windscreens.
An impact with a jet engine may severely damage that engine but very little else. The British CAA has been in contact with all major engine manufactures who were all of the belief that a drone would not cause an uncontained engine failure. Even if a collision with a UAV did result in a major engine malfunction, the FAA has mandated that an engine nacelle be designed to contain engine fragments so that penetration by engine debris of the fuselage, fuel tanks and other critical areas would be very limited. Virginia Tech University in the US did some computer simulations that concluded that a 3.5kg drone would severely damage the fan blades of a three-metre diameter turbofan engine in 1/200th of a second with drone debris within the engine reaching speeds of 1150kmh. Airline pilots are trained to deal with an engine suffering severe damage such as this. This training, conducted in a simulator, usually involves the engine malfunction occurring after V1, being the maximum speed that an aircraft can stop at and remain on the runway and the worst possible time for this to occur; the aircraft is committed to taking off after V1. Multi-engine turbine powered aircraft are designed to be able to fly away with an engine malfunction on take-off, so performance with an engine out is generally never going to be an issue. Even though an aircraft may not be destroyed, significant economic damage is caused to the operator by not being able to utilise the aircraft while it is being repaired. The other issue for aircraft is on final approach. This is a high workload environment for crew and any incident involving a drone could easily distract the crew from critical tasks.
In light aircraft though, an impact with a drone may result in significant control surface damage creating severe consequences as these aircraft are constructed of a much lighter material and the control surfaces are much smaller in comparison to larger aircraft. Not only could the aircraft be destroyed but numerous fatalities and injuries could be caused to those onboard as well as anyone within the vicinity on the ground should the aircraft crash.
Educating the Public
One of the problems being faced by aviation authorities worldwide is an ignorance, and/or lack of understanding by some drone operators, of the implications of flying a drone in the vicinity of aircraft and airports. DJI Innovations, the largest drone manufacturer in the world, have taken a very proactive stance in this regard. DJI have introduced a nine-question knowledge-based quiz on local regulations within their app in the United States, the United Kingdom and Australia with further countries set to come online. All questions must be answered correctly in order for the drone to fly. Should the owner choose to travel to another country with their drone, the questions will automatically update to those of the country that the drone will operate in. The FAA, CAA and CASA have given DJI their blessing. DJI also have geofencing included within their app thereby preventing drones being operated in areas where aviation safety or national security may be affected. A website has also been produced by DJI that shows no-fly areas as well as additional safety information that drone pilots can check. Additionally, CASA also produced an app (Can I Fly There?), which also shows airspace limitations for drones within Australia. DJI also produce videos and run workshops for new pilots where regulations are emphasised.
“…windscreens on transport aircraft have a design requirement to be strong enough to withstand impact with a 4lb bird at cruise speed. A bird though, is mostly comprised of soft tissue and fluid and largely disintegrates on impact…”
The FAA has also adopted a system that requires all drone owners to register, at a cost of $5.00 for three years. This allows the FAA to send out safety information upon registration as well as to communicate safety messages to operators. As of December 2016, over 616,000 users had registered.
The Threat to Airports
Technology has increased exponentially over the years. It is possible for someone with knowledge of model aircraft and radio to construct and fly a large fixed wing drone a good 80km with a substantial payload utilising mobile phone technology. Material and engines are easily available to purchase and are not traceable. Drones can also be parked in a hidden area and kept active with battery cells for a significant amount of time until commanded to lift off on a mission. GPS coordinates can also be pre-programmed into the drone allowing the device to automatically track to a target with no user input required after launching.
“…an attack was launched in Syria on four Russian military bases by 13 crudely made drones, each equipped with GPS and powered by what appeared to be lawn mower engines, with each carrying nearly half a kilogram of explosives…”
What about an attack on an airport? This may have been considered a figment of the imagination of a science fiction writer several years ago but is now a reality. Back in early January, an attack was launched in Syria on four Russian military bases by 13 crudely made drones, each equipped with GPS and powered by what appeared to be lawn mower engines, with each carrying nearly half a kilogram of explosives (PETN) surrounded by metal ball bearings. The Russian Defence Ministry reported that there were no casualties or damage resulting from the attacks. The Defence Ministry also stated that their Pantsir-S1 air defence systems shot down several of the drones and that they were able to capture some of them after their defensive electronic warfare systems disabled GPS and control signals to the drones.
Drone Defence Systems
Defence of civilian infrastructure requires different systems to that of military infrastructure. Numerous counter-drone systems are being developed by over 155 companies worldwide. These can range from SIM cards in drones to systems that enable detection including radar, acoustics, radio frequency (RF) detection and thermal heat as well as guns that disable UAVs, and raptor birds that are trained to intercept drones in flight, the most common systems being radar and RF.
Vodafone has commenced trials with technology that involves a SIM card and a 4G modem installed in drones. Vodafone has also developed a Radio Positioning System (RPS) specifically for drones. This allows tracking with a 50-metre accuracy by both the operator and air traffic control. Geofencing can also be transmitted by this system to a drone with the ability to force the drone to either land automatically or return to the operator if approaching an exclusion zone. Authorities can also take control of a drone and either alter its flight path or force it to land. This system is all well and good for commercially made drones that have the system preinstalled and with air traffic control systems that are compatible, however drone manufacturers must be prepared to design the installation of this hardware into their product. Drones of course can also be assembled from kits or self-designed and constructed, bypassing this system.
A good example of a counter-drone system is Ingegneria Dei Sistemi’s (IDS) Black Knight radar. The system is built-for-purpose and incorporates optical and thermal sensors to assist in the identification of a drone in flight. The system can detect Class 1 (mini and small) drones from 2km and identify the contact with the optical and thermal sensors shortly after detection when the turret slews to the target bearing.
The system provides 360 degrees coverage to permanent or mobile/transportable assets supporting both civilian and military users. Once an unauthorised drone is detected and identified by the operator, the jammers can be used to either disrupt the drone’s navigation or datalink back to the remote pilot. Jamming signals can be transmitted on GPS (L1/L2 band), 2.4GHz, or 5.8Ghz independently to force the remote pilot to navigate the drone themselves, provide the aircraft with an incorrect GPS solution (forcing it off course), disrupt communications which removes control from the remote pilot (the drone may return to home through internal logic) or work together to possibly force the drone to a controlled landing. The GPS jamming signal will only affect the drone, and the chances of causing disruption to legitimate users are minimal.
Another interesting counter-drone device is the DroneGun manufactured by DroneShield. There are several different versions available with a range of up to 2km. These also have the ability to jam GPS signals as well as the 2.4GHz and 5.8GHz controller frequencies. The operator has the option of either forcing the drone to land or return it back to its starting point, enabling the drone operator to be tracked. The DroneGun will never be Federal Communications Commission (FCC) certified thereby rendering it only useable by government agencies. The DroneGun has been used by the Swiss police and military at the World Economic Forum in Davos as well as Australian law enforcement agencies at the Commonwealth Games held at the Gold Coast.
The limiting factor on most counter-drone systems is that many countries have laws in place that restrict the use of jamming capabilities. Jamming may only be undertaken with express permission from government/military/federal agencies. Until legislative changes are made and governments are prepared to invest in these type of systems, drones will become an increasing threat.
Although many countries try to educate drone users, there are always going to be those users that push the legal limits. Authorities must ensure that appropriately severe penalties are applied and publicised in the media.
Given the massive increase in drone usage, and the ongoing terror threat, it is imperative that the types of systems described above are integrated into air traffic and airport security systems. Further education must also be undertaken by both drone manufacturers and governments, and wide spread publicity should be given to the punitive actions taken against miscreant operators.
Clayton Simmons possesses both a remote pilot’s licence and airline transport pilot’s licence. He also has a Master’s Degree in Policing, Intelligence and Counter-Terrorism and a Postgraduate Diploma in Aviation Industry Management. Clayton is endorsed on the Boeing 747 and currently flies Boeing 737s as well as being involved in the commercial drone industry.