Low Level RPAS

Low Level RPAS

56TH ANNUAL CONFERENCE, Toronto, Canada, 15-19 May 2017

WP No. 88

Low Level RPAS

Presented by TOC


This paper studies low level remotely-piloted aircraft systems (LL-RPAS) to examine recent activities, regulations and interactions with ATM. It also makes recommendations for ATC during encounters with very low level operations. This paper follows the previous IFATCA studies on RPAS that mostly covered the operational and professional issues of medium and large RPAS activities above 500 ft.


1.1 Low level remotely-piloted aircraft systems (LL-RPAS) are not only limited to hobby and entertainment purposes: technology is developing, performance is increasing and the prices are decreasing quickly. This attracts not only the interest of private users but also the interest of many companies to use drones for various purposes.

1.2 RPAS in general can operate much closer to the ground and to obstacles than manned aircraft can.

1.3 RPAS operate in airspace where other users operate too e.g. ultra-light machines, helicopters including emergency medical services, search and rescue, fire-fighting, police and border patrol and military flights of all kind.

1.4 A major threat to safety is the recreational use of (toy) RPAS by people who are generally less aware of the dangers and with few safeguards. The lack of aeronautical culture within small drone users decreases the safety level of low-level manned aircraft operations.

1.5 International and local air crew and ATCO associations, inter alia, are concerned about the potential reduction in safety levels.

1.6 Recently, there has been strong political support for developing rules on RPAS. However, regulations are not harmonised yet as member states have often formulated independent regulations to address growing needs while facing political pressure, as international standards are not yet available.

1.7 Several solutions might be applied to the aeronautical environment to mitigate the safety risks. Software- and hardware-based approaches are being developed by industry and evaluated by CAAs. Traffic management procedures, technologies and systems are being developed for low-level operations.


2.1 Use of small drones

2.1.1 RPAS in general can operate much closer to the ground and to obstacles than manned aircraft can. This allows LL-RPAS to inspect power lines or oil pipelines in labour-intensive and sometimes dangerous circumstances, provide fire-fighting support, acquire high definition video/images, provide express delivery and also precision agriculture. Using these systems can yield a better cost/benefit ratio and the environmental impact is usually smaller when compared to traditional manned systems. These types of inspections and activities are already taking place in many States. In general, RPAS are highly suitable for dull, dirty and dangerous operations.

2.1.2 It is commonly assumed that the airspace below 500 ft AGL is bereft of aircraft and is therefore relatively safe airspace for RPAS operations. Even below 500 ft AGL there is a large number of airspace users e.g. air ambulances, police or fire fighting, border control, military and newsgathering agencies. This applies even more to the airspace adjacent to airports, where arriving and departing aircraft operate. These operations are often unpredictable in time and place but all are subjected to the same rules of the air and should not be penalised or placed at risk by the coexistence of RPAS operations.

2.1.3 Another major safety threat is the recreational use of (toy) RPAS by people who are, in general, not aware of the dangers of operating in proximity to the other traffic and operate with few safeguards. Many of these untrained operators have no or limited knowledge about how and where they can safely operate an RPAS: they might not consider potential conflicts with other aircraft. These types of RPAS can easily penetrate airspace used by manned aircraft; a mid-air collision could potentially cause the loss of control of a manned aircraft operating too close to the ground to allow adequate recovery thus leading to disaster.

2.1.4 Several videos that depict aircraft operations shot by drones overflying airports are available to view on the web. Such operation of an RPAS could pose an extreme hazard to the safety of manned aircraft – not only the initial act itself but also its potential for encouraging emulation by others.

2.2 Media and reports

2.2.1 Reports appear in the media from time to time about LL-RPAS seen passing close to aircraft.

2.2.2 On 25th March 2016, the FAA released an updated list of pilot, ATC and citizen reports of possible close encounters with unmanned aircraft systems (UAS). The count is over 600 in the period between September 2015 and January 2016.

2.2.3 Since an official RPAS accident and incident database is missing, the European Cockpit Association (ECA) has started collecting information about such events. The ECA Drones Incident and Accident Repository (https://www.eurocockpit.be/pages/remotely-piloted-aircraft-systems-drones) (published in August 2015), without claiming exhaustiveness, illustrates significant incidents and accidents mostly but not exclusively in Europe.

2.2.4 On 12th June 2016, Dubai Airport closed its airspace for 69 minutes due to unauthorised drone activity, causing 22 flights to be diverted. For the same reason, Dubai Airport closed its airspace again on 28th September and on 29th October of the same year. It has been estimated that these closures cost about US$1 million per minute to the United Arab Emirates economy.

2.3 Market development

2.3.1 The market for RPAS is huge and many manufacturers produce their own devices with a wide extent of weights, performance and uses. The drone market is still a fledgling one, so the numbers will probably grow as the market develops. More drones will likely be sold as new competitors enter the market and prices fall.

2.3.2 The hobby drone market is growing very rapidly. TOC was not able to obtain current sales data but an estimate is that in 2015 the three biggest producers (Parrot, DJI and 3D Robotics) together sold about two million drones around the world.

2.3.3 Research firm Markets and Markets estimates that the global drone market will grow at a compound annual growth rate of 32% between 2015 and 2020 into a US$5.6 billion industry.

2.3.4 Google and Amazon are planning to start delivering packages by drone in 2017. Their plan is to deliver packages up to 2.5 kg by air in less than 30 minutes. On 7th December 2016, Amazon successfully completed the first trial of its project “Prime Air Delivery” (https://www.amazon.com).

2.4 Classification

2.4.1 As of 2017, classification of drones differs from state to state.

2.4.2 Even a small drone of relatively small weight is potentially very hazardous in regards of other aircraft. Several bird strikes have demonstrated that even impact with relatively small birds (below 200 g) can have catastrophic results for helicopters (Ambulance Helicopters like the EC-135, which are certified under regulation CS-27/FAR part 27, are not designed to withstand any bird strikes). As of today, drones are mainly classified according to weight and this does not make clear the risk to other aircraft.

2.4.3 In November 2015, Aero Kinetics Aviation completed a study on the consequences of flying RPAS in the national airspace system of the USA. The results in this paper are:

“Toy drones pose a catastrophic threat to manned rotorcraft in all phases of flight including cruise based upon their typical operating altitude.”

The report also noted that:

“Toy drones pose a real threat to fixed-wing aircraft primarily during approach and departure. Airliners faces a lesser potential for a catastrophic Drone Strike given they both reach cruising speed at significantly higher altitude and they have existing design regulations for impacts. Commercial aircraft are at the greatest risk during take-off and landing, and an engine ingestion drone strike during these phases of flight would cause severe damage to the engine and potentially a catastrophic failure, in either case resulting in damage to the aircraft and economic loss.”

2.4.4 The European Aviation Safety Agency (EASA) has been tasked by the European Commission to develop a set of European rules for drones. The result of EASA studies is the “Advance Notice of Proposal Amendment” (A-NPA). The study focuses more on “how” and “under what conditions” the drone is used, rather than only the characteristics of the drone. The document contains 33 proposals aimed both at commercial and non-commercial activities (since the same drone can be used for any activity). Part of the proposal is also that member states will designate which of their authorities will be responsible for enforcing the rules. The A-NPA defines two types of operations:

  • Commercial operations (aerial delivery, aerial surveillance and survey, other activities; and
  • Recreational use. An unmanned aircraft flying above the open sea poses less risk than a smaller one operated above spectators in a stadium. For this reason, the A-NPA proposes the following classification for RPAS based on the risk that the operation poses to third parties:

  • Open category (low risk)
    • A0 toys and mini drones (<1 kg)
    • A1 very small drones (<4 kg)
    • A2 small drones (<25 kg)
  • Specific category (medium risk); and
  • Certified category (higher risk).

2.5 Flight rules

2.5.1 Since 2014 there is visible and strong political support for developing rules on drones but regulations are not yet harmonised. EASA has been tasked by the European Commission to develop a regulatory framework for drone operations and proposals for the regulation of “low-risk” drone operations. In achieving this, EASA is working closely with the Joint Authorities for Regulation of Unmanned Systems (JARUS).

2.5.2 The IFR and VFR concepts are not applicable to RPAS flights. Alternatives to those traditional flight rules could represent the solution to permit interaction of manned and unmanned aircraft within the same airspace. As of today there is no specific regulation in regards to them because human actions are still required. Even where today’s auto-land, autopilot/flight director or TCAS features might look like autonomous procedures for manned aviation, the human part of the system still needs to be present in order to override the system in case it is necessary.

2.5.3 Due to their operating altitude, speed, shape and size, RPAS might not be detected at all by ATS surveillance systems. For the same reasons, RPAS are also difficult to be spotted and kept in sight from aerodrome control towers. Given the additional fact that they are usually many times smaller than other aircraft, they might not be visible to other airspace users, especially when the speed difference is taken into account. Small commercial RPAS might only have lights indicating battery state, GPS signal state or remote controller link state. As of today, there are not general requirements for colours/lighting system of RPAS.

2.5.4 While visual line of sight (VLOS) operations are conducted with pilots maintaining direct visual contact with RPAS all the time, this is not happening with extended visual line of sight (EVLOS) and beyond visual line of sight (BVLOS) operations. EVLOS operations allows pilot in command to rely on one or more remote observers to keep the RPAS in sight. Remote observers relay critical information and assist the remote pilot in maintaining safe separation from other aircraft (manned or unmanned). BVLOS means flying an unmanned aircraft without the remote pilot having to keep the RPAS in sight. Instead, the remote pilot flies the aircraft by instrument from a remote pilot station. RPAS operations are regulated differently with different minima requirements. A set of basic common rules should be defined to harmonise operations outside segregated airspace and near state borders.

2.5.5 The detect and avoid (DAA) concept, aims to ensure safe execution of an RPA flight and to enable full integration in all airspace classes with all airspace users. ICAO, in Annex 2 “Rules of the Air”, defines DAA as:

“The capability to see, sense or detect conflicting traffic or other hazards and take appropriate actions.”


DAA cannot be compared to the see and avoid (SAA) concept. According to ICAO Doc 9854 “Conflict Management”:

“2.1.7 Conflict management will consist of three layers: strategic conflict management through airspace organization and management, demand and capacity balancing, and traffic synchronization; separation provision; and collision avoidance.”


DAA is a concept integrating the second and third layer of the conflict management but is done by a single device. The redundancy of SAA offered by the pilot (the third layer) is missing.

2.6 IFATCA policy

2.6.1 IFATCA policy related to unmanned aircraft is:


IFATCA is opposed to the operations of any autonomous aircraft in non-segregated airspace.

All Remotely Piloted Aircraft Systems (RPAS) operations in non-segregated airspace must be in full compliance with ICAO requirements. Whether the pilot is on-board or not shall be irrelevant for the purposes of air traffic control, therefore the same division of responsibilities and liabilities as manned aircraft shall apply.

ATCOs shall not be held liable for incidents or accidents resulting from the operations of RPAS that are not in compliance with ICAO requirements, in non-segregated airspace.

Standardized procedures, training and guidance material shall be provided before integrating RPAS into the Civil Aviation System.


2.7 Pilots’ Association policies

2.7.1 The International Federation of Airlines’ Pilots Associations (IFALPA) published the following position:


“IFALPA believes that UAS technology is not capable of replacing human capabilities, particularly in complex and safety–critical situations. Therefore, IFALPA strongly opposes the use of UAS to supplant the role of pilots in any type of air transport operations.

The safe integration of UAS operations into civilian, non–segregated airspace can only be achieved if UAS are regarded in all ways as aircraft. UAS and their operations must comply with all existing rules and regulations applicable to other aircraft in the same class of airspace. It is not acceptable for such rules and regulations to be changed for manned aviation in order to integrate UAS and their operation.

As a subset of UAS, Remotely-Piloted Aircraft System (RPAS) should be fully certified and compliant with the provisions described herein before being allowed to operate in nonsegregated airspace.

Non-compliant UAS will require segregated airspace or mitigation by special authorizations.”


2.7.2 The ECA is concerned about a potential degradation of the existing high level of safety when considering the integration of RPAS in low-level airspace.

2.8 User registration and identification

2.8.1 A system of registering RPAS operators ensures that, in case of an event in which the operator or at least the owner of the RPA has to be known, he/she could be identified. Such a system may not in itself increase safety; however, knowing that they are not anonymous, operators may take greater care in where and how they use their RPAS.

2.8.2 In the USA, all RPAS between 250 g and 25 kg must be registered in the FAA UAS records. Registration costs US$5, is a simple web-based process and is valid for three years. RPAS must be engraved or labelled with the registration number provided by the FAA; heavier RPAS must be registered as aircraft. Thanks to free registration within the first 30 days of operation and the user-friendly system, nearly 300,000 devices were registered by January 2016. These numbers are encouraging but represent only about the 30% of the predicted holiday sales alone.

2.8.3 In Ireland, RPAS registration is mandatory above 1 kg. The Irish Civil Aviation Authority has started online registration for drones between 1 kg and 25 kg (excluding fuel but including any article, equipment or cargo attached at the start of its flight).

2.8.4 Ideally, RPAS and user registration should occur at the time of purchase but presently drones are sold everywhere (even on in-flight duty-free) so this would be difficult to achieve.

2.9 Aeronautical culture

2.9.1 Since there is no common RPAS licence yet, operators of RPAS have often very limited knowledge of the rules of the air and the operating principles of aircraft (especially rescue, state and aerial work flights). Due to lack of knowledge, they may not understand if and when they are endangering manned aircraft operation.

2.9.2 Many ANSPs, civil aviation authorities (CAAs) and institutions are opening specific web pages with the aim of educating users in the safe use of their drones. Moreover, some of them are also organising drone training courses. The UK ANSP NATS together with the UK CAA has developed a project called Drone Safe. This is a good example of an educational website (including a drone code – five simple rules to follow when operating an RPA) and RPAS pilot assistance thanks to an easy-to-use smartphone app – Drone Assist. The app, using an interactive map, supports the pilot in determining areas to avoid and as well ground hazards; the app also enables the sharing of position information with other app users. Similarly, the FAA developed the smartphone app B4UFLY. Recently SkyVector (an aviation charting and flight planning website) has added a graphical depiction of drone NOTAM, which the website calls DROTAM. The United States Department of Agriculture (USDA) as well the Forest Department together with fire fighters started an information campaign called “If you fly, we can’t”. In July 2015 fire fighter’s efforts were disrupted because of hobby drones flying in the fire area. Officials were forced to ground all the fire-fighting aircraft (such as air-tankers and helicopters) that would have helped the suppression of California’s major wildfire.

2.10 Safety Tools

2.10.1 Software application DJI, one of the major drone producers, is leading the market studying new safety system such as geo-fencing. The software helps to avoid inadvertent operation in locations that could cause safety or security concerns. Geo-fencing automatically prevents the device from taking off if within a no-fly zone or, if already in flight towards the location, will pause at the boundary and stop it from entering. The system is not perfect yet: if the RPAS is attempted to be flown before the GPS location is available, it might still fly into a no-fly zone. An application like geo-fencing software would make RPAS incapable of flying within a certain distance from an airport. It could even automatically limit the altitude of the drone if flying under departure/arrival paths. In September 2016, EASA released the second issue of the “Study and recommendation regarding unmanned aircraft system geo-limitation”. The proposals of this document (produced by a task force involving EASA and national aviation authorities’ specialists) are focused on the “open category” and the risk it might create to manned aircraft. It appears clear that such software would be desirable to be declared as mandatory. The implementation should be promoted to users in the way to let them understand that it is not a limitation to stop the enjoyment of operating RPA but a way to help them (and others) to have easy and safe operations in regards to any other people and aircraft. This would represent unwanted additional costs for operators but it could also lead to a new business. Companies might be interested in the competition of creating the most up-to-date, reliable, user-friendly, CAA-certified aeronautical database for drones.

2.10.2 Hardware application Sagetech Corporation has developed a small and light ADS-B (just 150 g) but the price of this device is still high. Users might be reluctant to spend money to equip their RPA with an ADS-B system. Due to weight restrictions, only a very limited and possibly inadequate DAA system could possibly be installed on board an RPA. Nevertheless, foreseeable miniaturisation and nanotechnology could shrink that hardware to fit into pocket-sized devices in the future. The possibility would then be up for consideration. Barometer vs. GPS altitude A peculiarity of GPS applications is that altitude/height is geoid-based and not pressurebased. A GPS device like a drone could then give a vertical position indication that differs from the one used by commercial aviation, where barometric altitude is the standard.

2.10.3 RPAS detection and display As of today, there’s no specific regulation requiring RPAS to be equipped with devices for the transmission of identification and position. This makes almost all the RPAS flying at low level classified as non-cooperative targets in regards of the present ATS surveillance system. The shape and size of RPAs, surrounding terrain, buildings and vegetation compromise their detection from ATS surveillance systems. High-security sites, major airports and VIP areas are requesting the industry to mitigate possible threats. The detection and display of RPAS (on integrated or separate display) is already possible using new generation radars (such as the “3D holographic radar™” by Aveillant (https://www.aveillant.com)) combined with specific software alerting whenever unauthorised drones infringe determined airspace. Different trials at different levels are already taking place. Whenever it will become effective, all the equipment and procedures adopted should meet established aviation standards and criteria.

2.11 Security

2.11.1 The open nature of RPAS is susceptible to hacking. RPAS could be hijacked and used as a weapon against other airspace users and/or targets on the ground. ADS-B signals could be easily received and, if jammed, could compromise the safety of other DAA systems or give unreliable information to ATCOs. Geo-fencing databases might be subject to a hacker’s attack and be infected with malware that would be downloaded by all RPAS.

2.11.2 There are companies developing and testing different devices capable of electronically disrupting the control of the drone, neutralising it so no remote action, including detonation, can occur. These devices are currently neither approved nor certified. MAs should be aware on the effects that they might have on aviation.

2.12 Unmanned aerial vehicles traffic management (UTM)

2.12.1 In 1920, with the increase of air operations, the first fatal incidents started to occur. As result of this, the era of ATC (later part of the ATM concept) started.

2.12.2 An ATM-like system is needed in order to safely enable widespread civilian RPAS operation at lower altitudes. UTM is the service that is in project and development phase already by some national agencies and providers.

2.12.3 The goal of UTM is to enable safe and efficient low-altitude airspace operations by providing services such as: authentication, airspace design and dynamic configuration, dynamic geofencing, severe weather and wind avoidance, congestion management, terrain avoidance, route and re-route planning, separation management and contingency management.

2.12.4 UTM, ideally, is an autonomous system and will not require a human operator to monitor every vehicle continuously.


3.1 IFATCA policy on RPAS is valid but there is a risk that it will not be sufficient in the near future with regards to the low altitude activity of these devices. We have to keep in mind that the integration process of RPAS is not reversible. RPAS activities in lower airspace are not under control. New criteria, which satisfy both airspace users and ATM, should be studied in order to achieve the highest possible level of safety.

3.2 It is established that a 20 kg RPA flying above the Atlantic Ocean is not as dangerous as a 1 kg drone flying above a crowded stadium or too close to an airport/airfield. Studies taking in consideration the kinetic energy of the impact (and not the weight/dimension) of the RPAS demonstrate the danger of small and relatively light devices. RPAS should be classified according to a risk assessment rather than weight/dimension.

3.3 EVLOS should be included in BVLOS operation. Both of them should be only conducted under conditions where conflict with other aircraft is not possible (NOTAM notifying the activities to other users are not sufficient). Only a proper and effective implementation of UTM could lead to safer EVLOS/BVLOS operations outside segregated airspace.

3.4 Standardisation should be required for altimeter readings (baro-altimetry or geo-altimetry). Height should be technically limited or at least always visible to RPAS pilots.

3.5 The visibility of RPAS should be maximised, achieved through lights and/or colours.

3.6 Even if the use of identification or detecting devices (such as ADS-B or new generation radars and displays) might be desirable to enhance the safety levels, studies should be conducted in order to determine the impact of those on the ATC surveillance and clarify ATCO’s responsibility framework and system liability.

3.7 National CAAs and ANSPs together with drone producers should be active in educating the users in aeronautical matters. Training should include an awareness campaign, airmanship, liability and insurance issues. Training for an RPAS licence should not omit principles of just culture, which encourages the reporting of safety issues in the interest of the whole aeronautics system.


4.1 It is recommended that the following is added to existing IFATCA policy:

IFATCA encourages education and awareness campaigns on the use of RPAS for the general public.

IFATCA urges the development and implementation of technology to prevent airspace infringements by RPAS.

Contingency procedures and controller training shall be provided for the management of infringements by RPAS.

4.2 It is recommended that the work programme 2017-2018 for TOC and PLC should include the use and liability of RPAS surveillance information provided to controllers.


IFATCA Technical and Professional Manual 2016 – AAS 1.10 OPERATIONAL USE OF UNMANNED AIRCRAFT (UA).

ICAO DOC 9854 “Global Air Traffic Management Operational Concept” – 2.1.7 “CONFLICT MANAGEMENT”.

EASA, A-NPA 2015-10

EASA, EASA/NAA Taskforce Report on “Study and recommendations regarding unmanned aircraft system geo-limitations”

European Parliament, Directorate-General for Internal Policies – Policy department B: structural and cohesion policies, study on “Research for Tran-Committee – Safe integration of drones into airspace”.

IFALPA Position Paper on RPAS, https://www.ifalpa.org.

ECA (European Cockpit Association) position paper on Low Level RPAS 15_0324, https://www.eurocockpit.be.

FAA UAS Sighting Report 21 Aug 2015, 31 Jan 2016, https://www.faa.gov.

The Aviation Herald, https://www.avherald.com.

Battelle, Battelle Dronedefender™, https://www.battelle.com.

Sagetech Corporation, https://www.sagetechcorp.com.

DJI, https://www.dji.com.

Aero Kinetics Avionics, LLC. Paper study on “The real consequences of flying toy drones in the national airspace system”.

AMAZON, https://www.amazon.com.

Dronelife, https://www.dronelife.com.

Markets & Markets, https://www.marketsandmarkets.com.

Irish Aviation Authority, https://www.iaa.ie.

NATS UK, https://www.nats.co.uk.

Transport Canada, https://www.tc.gc.ca.

DRONESAFE UK, https://www.dronesafe.co.uk

D-FLIGHT Italy, https://www.d-flight.it

JARUS-RPAS, The Joint Authorities for Rulemaking on Unmanned System, https://www.jarus-rpas.com.

AVEILLANT, https://www.aveillant.com.

Last Update: October 1, 2020  

January 17, 2020   872   Jean-Francois Lepage    2017    

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