In January 2023, the Transportation Safety Board of Canada (TSB) released its investigation report into the August 2021 collision between a drone and a small aircraft near Toronto/Buttonville Municipal Airport, Ontario. There were no casualties, but the aircraft was damaged and the drone destroyed.

According to one of the key findings of the accident report summary: “The investigation found that the Cessna pilots were unaware of the presence of airborne RPA (remotely piloted aircraft) traffic in the vicinity and, due to several factors, the active scanning that is part of the see-and-avoid principle was unsuccessful in identifying the conflict. “Additionally, York Regional Police policy does not require that visual observers be trained crew members, and the RPA pilot did not brief the visual observer on his role and responsibilities before the operation.”

The current users of very low-level (VLL) airspace flying in visual flight rules (VFR) conditions – private aircraft, hang gliders, gliders, balloons – are about to be joined by a new generation of VLL airspace users, including cargo and surveillance drones, electric vertical take-off and landing (eVTOL) aircraft and flying cars. The business plans of these new entrants are extraordinarily aggressive and based on a very fast ramp-up of operations once the necessary rules and standards are in place. So VLL is about to get very busy. While UAS traffic management (UTM) and U-space areas have been designed to ensure the safe separation of uncrewed aircraft in busy VLL airspace, many in the industry are starting to wonder whether the current see-and-avoid principles used to underpin VLL operations in more remote areas will continue to work once the newcomers arrive. Especially, as looks likely, there will be dynamic mixes of crewed and uncrewed aircraft equipped with different conspicuity and see-and-avoid systems.

But others see this a major opportunity for industry to fix a problem that, until now, has been the sole preserve of regulators and air navigation service providers (ANSPs). The sheer scale of the challenge means that, for the moment at least, regulators appear content to see whether, with minor modifications, VLL airspace users can continue to use the current see-and-avoid principles that underpin general aviation operations worldwide.

In the UK, the Civil Aviation Authority (CAA) has outlined a plan for the voluntary submission of flight intent data for flights in the lower airspace “to be processed and shared to and by appropriate service providers” as part of its latest airspace modernisation strategy. The US Federal Aviation Administration (FAA) has said it does not want to make any major changes to the rules for traffic below 400ft.

In Europe, VLL drone traffic management U-space areas will be identified by States where the new European Union U-space regulations will apply. “But U-Spaces will only be economically viable options whenever there is a certain amount of drone operations taking place in the specific area,” said Nathanel Apter, a UAS compliance expert based in Switzerland. “Drone delivery is targeting remote locations or specific routes where we do not expect to see an important volume of drone operation taking place in the very near future. So for those areas, U-Space is not an economically viable option in the near future and different strategies are needed to ensure that drone operations can be integrated in those airspaces...for instance, defining procedures based on existing aviation means to co-ordinate with manned aviation – such as NOTAMs.”

How will the low-level airspace community come together to develop policies, procedures and technologies to ensure traffic can be safely accommodated?

One obvious solution is to keep small UAS traffic below 500ft and general aviation crewed aircraft higher – as required by the International Civil Aviation Organization (ICAO). But as a recent Eurocockpit briefing paper on VLL acknowledged: “The exclusion of manned aviation from certain parts of the airspace for the benefit of UAS operation is neither desirable nor practicable.” 

It continued: “The height/altitude measurement equipment on UAS and smaller aircraft or sports equipment (eg, kites, parachutes), is usually not certified up to the standard of commercial manned aviation and if operating at the same indicated altitude, a significant difference can be expected. “Furthermore, it is impossible to pilot aircraft at the exact same altitude for a prolonged time, and a height deviation of plus or minus 100 feet is usually deemed acceptable.”

If new procedures or airspace classifications are not the answer, how about new technology?

“It needs new technology for airborne equipment as well as for the ground nfrastructure to create an ecosystem of airborne and ground infrastructure to ensure ‘see-and-avoid’ in VFR airspace,” said Dr Guenter Graf, Frequentis vice president of new business development. “A precondition is the transition from human-centric flight information services towards machine-centric decision making based on a 100% situational awareness – that is, co-operative targets. Automation would be essential for efficiency and safety reasons and, in general, the accommodation should follow the principle of, the better equipped, the better the access to the airspace.”

In the USA, for example, the BVLOS aviation rule-making committee (ARC) working with the FAA on new UTM rules, has recommended that in certain VLL airspaces drones equipped with Traffic Awareness Beacon System (TABS) – a non-regulated, low-cost device that makes small aircraft visible to others equipped with collision avoidance systems – should have right of way over crewed aircraft that are not equipped with ADS-B or TABS.

There is no shortage of detect-and-avoid and conspicuity technologies entering the market, both advisory and regulated. In the past, airspace users would have to wait for ICAO to identify and mandate appropriate technologies and procedures and then for States to implement the mandate. But perhaps there is another way. Perhaps VLL airspace users, new and old, can start re-defining the way detect-and-avoid systems operate. 

In regulated airspace, separation is assured by mandated services: air traffic control and the carriage of aircraft collision avoidance systems. In unregulated airspace, at very low-level, a more informal mixture of voluntary intent reporting, unregulated position reporting systems and ADS-B equipment can somehow work together to provide users with an accurate picture of who is flying where, depending on local equipage behaviours.

But while there are clear benefits for VLL airspace users to co-operate on new safety procedures, the issue of securing airspace, rather than developing deconfliction procedures, will require some new kind of regulatory oversight. “What is needed is a proper system to identify drones that fly with permission, and to be able to quickly assess that an aircraft/drone is not allowed to fly in a specific area,” said Frequentis’ Dr Graf. “And then police need to come up with procedures for what to do next. Since a 100% coverage of drone detection radars would have a tremendous cost impact, we assume that such detection systems will be deployed to protect critical infrastructure in the first step. In the current state, we should use available technology to create a common situational awareness picture, which could be distributed to all co-operative
airspace users, including drones. “If the good ones are known, the risk of false alarms using drone detection systems are mitigated.”

One of the challenges, according to Assaf Monsa, chief technology officer at counter-UAS company D-Fend, is that there will be no part of VLL that drones and other new airspace users will not want to use. And you cannot regulate for that. “So we have built a framework in which everyone is co-operating and the problem of non-cooperating drones has been left for later,” he said. “The question we are all facing is how we get to any acceptable level of safety – and if you don’t have some kind of surveillance technology able to identify non-co-operative traffic, then you are not safe. Even if all air traffic were properly mapped and tracked, I still fail to see the parts in the framework that would enforce the safety rules in case a rogue element or an irresponsible or careless player enters the airspace, and without that, how can we make sure that no part of this air traffic drops on us from a 300-feet altitude?"

But, for the moment, that is not industry’s concern. For most drone operators, 2024 is the year when the rules, standards and technology maturity levels will all be in place to allow for autonomous BVLOS operations – effectively kick-starting the fully commercial phase of the global drone sector. How these new autonomous systems will interact with legacy general crewed aviation traffic is one of the great current unknowns.


Article originally published in Air Traffic Management magazine, issue 1, 2023.  Want to receive all of the latest stories as soon as they are published? Register now for your free digital subscription.