Applications that can benefit from using drones are increasing worldwide, almost daily. However, commercial users of drones are being constrained by generalised legislation, which is difficult to understand and expensive to implement. A much- contested application – and one that is illegal to undertake for the vast majority of drone operators – is using drones beyond visual line of sight (BVLOS).
Operating a drone BVLOS refers to flying such aircraft beyond any point where it can be seen with the human eye and, although technology exists for drones to be operated in such a manner – either through a preprogrammed global positioning system (GPS) waypoint-to- waypoint flight path or a digital piloting interface – doing so is almost unanimously unauthorised by any airspace authority.
Globally, countries’ airspaces are regulated and restricted by civilian aviation authorities. South African airspace is regulated by the South African Civil Aviation Authority (SACAA), with the deconfliction of airborne vehicles (only those identifiable by radar) falling under the regulation of air traffic controllers (ATCs).
Locally, only State-owned defence systems developer Denel Dynamics is authorised to operate unmanned aerial vehicles (UAVs) in BVLOS mode. There is significant debate about other UAV operators conducting various forms of BVLOS operations in the country, but the extent to which these are authorised by the SACAA is unknown, but mostly regarded as illegal, as the SACAA is unwilling to authorise civilian drone operators to undertake BVLOS flights.
Denel Dynamics developed and operates the Seeker series of UAVs and operates the Seeker II UAV locally, with Seeker I being phased out. Seeker II is a 7-m-wingspan military-spec aircraft that can operate through microwave and ultra-high-frequency radio at a radius of 250 km from its remote-controlled base station and at a service ceiling of 18 000', with an endurance of 10 hours. Its maximum takeoff weight is 310 kg, which includes 80 ℓ of fuel and up to 50 kg of payload.
Payload refers to any external fixture fitted to the aircraft, which is in most instances an optical payload comprising colour, infrared- and thermal-imaging cameras.
To gain better insight into how Denel Dynamics has managed to obtain authority to fly aircraft in BVLOS mode and the implications of operating a large aircraft at high altitude several kilometres away, Engineering News spoke to Denel Dynamics UAV business GM Sello Ntsihlele about the steps required to safely and legally undertake such a UAV operation.
He points out that performing BVLOS flights requires a dedicated crew, with members having specific duties and the necessary expertise. A Seeker UAV requires two pilots: an ‘internal’ pilot to fly the aircraft from within the ground station using digital systems, and an ‘external’ pilot who typically performs the takeoffs and landings through visual line of sight. The external pilot uses a radio control module similar to that which a conventional hobbyist radio control pilot would use and is based outside the ground station.
A Seeker UAV also requires a communications technician (similar to a flight engineer in conventional aircraft) who manages the uplinks and monitors the general technical health of the aircraft.
An observer is also required to operate the optical payload. The observer could play a vital role in emergency situations, during which the pilot requires visual imagery of where the aircraft is heading and what is in front of it.
To ensure a Seeker UAV is prepared for flight, a team of two technicians is typically required to set up the aircraft and perform ground-based preparation duties such as the assembly and disassembly of the aircraft, fuelling and powering up systems and the engine, as well as arresting the aircraft after landing (it has no brakes and relies on an arresting system similar to that used on aircraft carrier ships).
This team of personnel plays an integral part in making every flight as safe as possible and ensuring fast and appropriate reaction to dynamic situations and emergency scenarios. For instance, having separate pilots and communications technicians means that key personnel do not have to abandon their duties to attend to other matters when systems fail or unforeseen circumstances arise.
Ntsihlele provides an example of how teamwork played a critical role in mitigating the loss of the very first Seeker II UAV. “Our very first flight of Seeker II lasted 28 minutes . . . and the flight personnel were in control for only four minutes,” he says. In this instance, the crew relied on the built-in ‘return home’ fail-safe function of the aircraft, which flew the aircraft back to the takeoff point, after which it went into a holding pattern until the command link could be re-established. This gave the technical team enough time to resolve the issue and regain control of the aircraft, leading to the safe landing of the aircraft.
Manned Aviation Lessons
The success of Seeker and its BVLOS capabilities and safety record stems from Denel Dynamics’ having developed the aircraft in line with the many safety features of manned aircraft.
Key equipment used on the Seeker UAV to ensure it can be located, tracked and identified by its crew, ATCs and other aircraft includes a transponder, long-range very-high frequency radio, an altimeter, GPS and navigation lights and strobes.
Seeker II uses a Mode C transponder, which receives a signal from radars used by ATCs and their various repeaters based around the country to identify aircraft, their location, speed, heading and altitude. Such a transponder receives a signal from a radar and then returns an enhanced signal with the relevant information about the aircraft to assist ATCs in determining where various classes of aircraft are, while airborne. ATCs use this information to coordinate various classes of aircraft into segregated airspaces as a primary collision-avoidance mechanism. For instance, helicopters and light aircraft are generally assigned to operate at low to medium altitudes, with larger aircraft operating at higher altitudes. Commercial jetliners operate at even higher altitudes, especially at cruising altitude.
Essential to ensuring that every flight is performed as safely as possible is the compiling of an in-depth safety case, which is a key planning phase before any BVLOS operation proceeds to an advanced stage, says Ntsihlele.
The Seeker flight teams compile and file safety cases for every BVLOS operation, and submit them to the relevant aviation sector oversight authority, which, in most cases, is the SACAA. When conducting military operations, however, the safety case is also submitted to the relevant military oversight authority.
Once the SACAA approves the safety case, Ntsihlele notes, ATCs need to be advised of the flight and air notices may need to be issued in advance of the flight, including notices to airmen as an advisory measure to inform pilots operating in the vicinity of where the UAV will fly.
In an ideal situation, the various landowners over which any such UAV will fly should also be notified, with approval being sought from them; however, Ntsihlele says this can be difficult, as some airfields and airports have different owners and operators. For example, Skukuza Airport, in the Kruger National Park, is owned by South African National Parks, but operated by SA Airlink, thus requiring permission from both parties to take off, land and fly over.
When Denel Dynamics compiles safety cases for Seeker operations, the main aspects covered in the case are the aircraft’s intended operating parameters (flight path, altitude and airborne time), no-go areas, emergency and fail-safe procedures, as well as location geography (the lay of the land, its features and topography).
Denel Dynamics has incorporated several safety features into Seeker UAVs.
Many of the components are tested and developed in-house to accurately determine the mean time between failure (MTBF) of critical and key components. Thus, specific components can be identified as requiring attention before they reach the end of their useful life span. This enables technicians to inspect, replace or repair the component before it fails, thereby preventing failure during operations, which could lead to loss of control of the aircraft.
Many UAVs available on the market to general users use an array of components that either have poor data on their MTBFs or their MTBFs cannot be determined. A significant number of these components rely on consumer-grade electronics, making it difficult to predict when certain components might fail. Consequently, this leads to safety uncertainties, which are exacerbated when UAVs are used in BVLOS operations, because any sudden loss of control or power when a UAV is out of sight can lead to unforeseen accidents in areas that are difficult to access or locate.
Other safety measures taken into account for any BVLOS flight of Seeker UAVs include system integrity checks of the digital on-board hardware and software, as well as control surface tests and engine runs.
Compiling safety cases for flying over the same site becomes easier with each successive instance as the terrain and its implications are understood, thus facilitating the drafting of cases and streamlining the approval process by an oversight authority.
Therefore, using the same UAV with known safety features and easy-to- determine MTBFs simplifies and accelerates the process, as a generic- aircraft safety document can be used as a template, which includes the simple updating of the MTBFs and the list of operational safety features.
Therefore, a safety case should account for any eventuality in the use of a UAV in BVLOS mode in a specific environment and should plan for different reactions to an array of situations, from a best-case scenario in which everything goes according to plan to a worst-case scenario, in which a UAV will be lost over a densely populated area.