As George Bernard Shaw once said “Both the optimists and the pessimists contribute to the society. The optimist invents the aeroplane, and the pessimist the parachute”. All over the world, numerous initiatives and demonstrations have shown the multiple benefits of drone operations, that is the optimists’ work. Now the pessimists are also at work to prevent malicious use of drones.
The air traffic can be divided into cooperative and non-cooperative traffic. The cooperative traffic is equipped with avionics facilitating its detection. The non-cooperative traffic has no such equipment and detection is solely based on ground or onboard sensors. It is important to note that detecting cooperative traffic is a lot easier and more precise than detecting non-cooperative traffic. This is why many experts advocate for all low altitude traffic to be cooperative, at least in high density airspaces, and a proposed solution is to use ADS-B. This solution seem acceptable considering that a large part of the existing traffic is already required (or will be soon) to carry ADS-B out, the technical solutions exist and they are affordable both in terms of SWaP (Size, Weight and Power) and cost. Now, a crucial questions remains: is it possible to introduce hundreds of ADS-B users in already busy (radio frequency wise) airspaces without disturbing the performances of existing systems, e.g. ATM systems ?
To answer this question, the MITRE conducted a study on the impact of equipping low level drones with Universal Access Transceiver (UAT) ADS-B. Both air-to-air and air-to-ground communications were considered. According to this study the crucial parameters are the traffic density and ADS-B transmission power. The following table, extracted from the study, shows the probability to decode a message depending on drones density and transmission power with values in bold being acceptable for ATM applications. With a density of 5 drones per square kilometer the emission power cannot be higher than 0.01W, which strongly limits the communication range, though experiments to know the precise range depending on the transmit power should be conducted.
Overall, the results of this study show that using ADS-B UAT in high density airspaces will prove difficult has reducing the transmission power of ADS-B is likely to decrease detection ranges and impact safety. For the particular case of UAT, considering the fact that it is only used in the US, principally aimed at General Aviation (GA) and with the current grow in GA traffic, the FAA is unlikely to approve such solution to make the drones cooperative. From a broader perspective, the study showed how quickly a cooperative method can overload a communication mean. Having only cooperative traffic is desirable but this kind of study make it look like an unreachable objective. For now…
According to the JARUS operational categorization, drone operations fall into one of three categories: A, B and C (or Open, Specific and Certified in EASA vocabulary). Flying in category A just requires to follow a fixed set of rules (altitude limitation, mandatory equipage, etc) while flying in category C requires a certified drone system. To operate in category B, an operator needs to demonstrate that operational risks are mitigated by available systems; such demonstration requires a risk assessment approach.
However existing safety tools are complex to use and not always suited to drone operation specificities. In order to provide adapted, accessible and universal tools to the drone community, the JARUS WG-6 developed the Specific Operations Risk Assessment (SORA), a somewhat simple yet powerful methodology allowing to perform risk assessment for drone operations. The full description of the SORA methodology has been recently published for external consultation on the JARUS website.
Though it is unlikely that using the SORA will be mandatory (other risk assessment methods will remain an option), its design will probably make it the best choice for operators willing to build a safety case. So if you plan on using drones in category B scenarios, you can start reading this document as it is likely to become your bedside book. For those interested, we will publish a more detailed article on the SORA methodology in the months to come.