Conspicuity and ATS Surveillance

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Conspicuity and ATS Surveillance

59TH ANNUAL CONFERENCE, Singapore, 30 March – 3 April 2020

WP No. 87

Conspicuity and ATS Surveillance

Presented by TOC


IMPORTANT NOTE: The IFATCA Annual Conference 2020 in Singapore was cancelled. The present working paper was never discussed at Conference by the committee(s). Resolutions presented by this working paper (if any) were never voted.


This paper provides information about Electronic Conspicuity (EC) which aims at improving the visibility of unknown VFR traffic in ATS surveillance environment. The concept and development of EC, as well as implication to ATC of integrating EC in current Air Traffic Management Systems (ATMS) are discussed. Further in-depth studies in various aspects are suggested to be carried out prior to full adoption of EC in current ATMS.


1.1 “Conspicuity” comes from the word “conspicuous”, which means (According to ““):

“easily seen or noticed; readily visible or observable” or

“attracting special attention, as by outstanding qualities or eccentricities”

1.2 With an increasing amount of traffic in both controlled and uncontrolled airspace, there is a raised concern about the visibility of unknown VFR traffic. Debate on conspicuity versus ATS surveillance, as well as the effect of electronic conspicuity on pilots and controllers’ situational awareness of unknown VFR traffic were brought up.

1.3 This working paper briefly provides background information regarding Electronic Conspicuity (EC) solutions and focuses on the advantages of improving aircraft conspicuity in surveillance systems through discussion on operational and technical considerations. Effects on ATC operations by integrating EC data into Air Traffic Management System will be covered.


2.1 Current rules and regulations for VFR separation

The ICAO Annex 11 “Air Traffic Services” details the standards and recommended practices for types of services and separation provided by ATC in different types of airspaces. In certain types of airspace, like Class E airspace, traffic information is provided by ATC when practicable, for VFR traffic to separate between themselves; while in Class F or G airspace, there is only flight information service provided to VFR traffic.

According to ICAO Doc 4444 (ICAO Doc 4444 sixteenth edition, applicability date 10 November 2016), “flight information service” is defined as:

“A service provided for the purpose of giving advice and information useful for the safe and efficient conduct of flights”

ATC units responsible for controlling Class F/ G airspace are not required to be supported by a surveillance system, while transponder installation on VFR traffic operating in these airspaces is not mandatory. Under these circumstances, “See and Avoid” remains as the fundamental principle for collision avoidance.

2.2 Principles of “See and Avoid”

“See and Avoid” has been defined by Federal Aviation Administration (FAA) in Regulation 14 CFR Part 91.113 (b) as follows:

“When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each per- son operating an aircraft so as to see and avoid other aircraft. When a rule of this section gives another aircraft the right-of-way, the pilot shall give way to that aircraft and may not pass over, under, or ahead of it unless well clear.”

According to an article published in “Proceedings” (Vol. 143/1/1367, Jan 2017) from US Naval Institute, three steps are required for pilot to respond effectively in order to avoid traffic:

“First, the pilot must recognize the indication and conceive a correct response (reaction). Next, the pilot must translate the correct response into motive force (motor response). Finally, the motive force must be translated to the appropriate control input (such as a stick, yoke, or throttle). Research has shown the reaction step takes on average 230 to 250 milliseconds.”

According to the Advisory Circular AC No.: AC 90-48D published by Federal Aviation Administration (FAA) regarding the subject “Pilots’ Role in Collision Avoidance”, the composition of response time to traffic could be 12.5 seconds minimum. The diagram below shows the sequence of actions from recognition of traffic to avoidance manoeuvre.

Another study concerning Airproxes and Collisions of Aircraft (BFU 803.1-17) carried out by the German Federal Bureau of Aircraft Accident Investigation (BFU) was completed in January 2017. It concluded seven causes for airproxes and collisions of VFR aircraft as follows:

  1. The performance limitations of the human eye
  2. Not seeing the conflicting traffic (pilot and air traffic control)
  3. Late recognition of the conflicting traffic
  4. Insufficient and late avoidance manoeuvre
  5. Late or inaccurate traffic information
  6. Misinterpretations of the pilots involved
  7. Non-adherence to regulations and procedures

These studies revealed “seeing and recognition of the aircraft” as the preliminary and crucial stage in any avoidance manoeuvre. Inarguably, improving conspicuity of aircraft could greatly assist pilots in “See and Avoid” actions and eventually improve the margin of safety. The following discussion focuses on the conspicuity of General Aviation Aircraft operating under VFR.

2.3 Improving conspicuity of VFR General Aviation Aircraft

In 2004, the Federal Ministry of Transport and Urban Affairs of Germany (Bundesministers fur̈ Verkehr, Bau- und Wohnungswesen) carried out a study regarding recognizability of gliders and small powered aircraft (BEKLAS, “Erkennbarkeit von Segelflugzeugen und kleinen motorisierten Luftfahrzeugen”).

The final report of BEKLAS suggested:

“Aviation is based on the basic principle of “see-and-avoid”, often translated as “seeing and being seen” in German. Although it comes from the early days of aviation, this concept is still valid today. As the name implies, it is vital to be able to see other traffic and be seen by other traffic to prevent collisions. The core element here is the ability of the pilot to understand other aircraft, to estimate the course and speed, and then to derive the right action for the situation. “

Nonetheless, visual conspicuity of an aircraft depends on many factors including weather (e.g. presence of cloud blocking direct visual contact between pilot and concerned traffic), the construction of aircraft as well as the human eye performance (recognition of slow change in terms of size) etc.

Take gliders as an example (BEKLAS, 2004):

“Gliders can best be seen when the rudder with the fuselage, or, with commensurate bank angles, the wing depth reflects the sun light and impresses by their size. However, during stationary circling flight this is almost never the case. Due to a circle time of approximately 20-30 seconds there are only less than five seconds per perspective.”

These limiting factors have thus encouraged the development of various systems to improve aircraft conspicuity in electronic format, so as to assist pilots in applying the “See and Avoid” principle for collision avoidance, as well as to improve situational awareness of controllers in traffic management.

2.4 What is Electronic Conspicuity (EC)?

Generally speaking, Electronic Conspicuity means the visibility of aircraft in electronic format. As defined in the “Airspace Modernisation Strategy – Electronic Conspicuity Solution, A calls or evidence on a new strategy” (CAP1777) published by the UK Civil Aviation Authority in March 2019:

“Electronic conspicuity (EC) is one of the most important AMS (Airspace Modernisation Strategy) initiatives because of its potential to increase safety benefits and save lives by reducing the likelihood of mid-air collisions and infringements (when an aircraft makes an unauthorised entry into controlled airspace). EC is an umbrella term for technologies that can help airspace users and air traffic services (ATS) to be more aware of the aircraft operating in the same piece of airspace, strengthening ‘see and avoid’ with the ability to ‘detect and be detected’. The phrase EC solutions refers to the devices, systems and infrastructure that bring these technologies to market and ensure they are interoperable. Airborne transponders, moving map displays, air traffic data displays (TDDs), ground-based antennas and satellite surveillance services are all examples of EC solutions. The information generated by EC solutions can be presented to pilots and air traffic services (ATS) visually, audibly or both.”

Technically speaking, TCAS (Traffic Collision Avoidance System) -which is widely installed in commercial aircraft- belongs to one of the EC solutions. Various avionics manufacturers have developed similar systems for General Aviation aircraft. These systems, which supports “See and Avoid” in an electronic way to indicate other aircraft with a transponder, ADS-B signal or FLARM signal, could also be considered as one of the EC solutions and are commonly found installed in VFR general aviation aircraft.

What is FLARM? According to the official website of FLARM system ““:

“FLARM was invented in 2004 by three Swiss glider pilots/engineers, following many fatal mid-air collisions between gliders. Despite the VFR-principle of “see and avoid”, in many situations it’s virtually impossible to see the other aircraft. At that time, mid-air collisions represented the most common cause of fatal accidents in gliding. Most accidents also happened in good visibility and during daylight.”

In 2010, PowerFLARM was developed to incorporate the reception of transponder Mode C/S and the ADS-B signal:

“PowerFLARM was made fully compatible with all Classic FLARM devices, but was designed to be much faster and have substantially higher power and range. PowerFLARM has antenna diversity, meaning it’s possible to have one antenna on top of the aircraft and one below. It also comes with an ADS-B and transponder Mode-C/S receiver, to maximise the number of aircraft that can be detected.”

The above-mentioned systems provide improved aircraft conspicuity, but their electronic signals and transmission channel are not interoperable and are virtually incompatible to each other. Though PowerFLARM, the improved version of FLARM, could receive the signals from Mode C/S transponder and ADS-B, the FLARM signal being transmitted out could not be received by Mode C/S transponder and ADS-B system since FLARM systems communicate at 868 MHz while the ADS-B system transmits signals at 1090 MHz. On the other hand, due to lack of standards widely accepted by the aviation industry, not all aircraft equipped with EC solutions support the “See and Being Seen” principle. EC systems installed could be receiving signals only (See), transmitting signals only (Being Seen), or supporting both reception and transmission of signals (See and Being Seen).

Nonetheless, the Electronic Conspicuity Working Group (ECWG) in UK concluded that:

“it would be possible to develop an industry standard for an EC device that uses radio frequency (RF) and is based on ADS-B extended squitter (ES) technology. This provides more useful information to other airspace users than other solutions, while offering low cost and low power consumption. The ECWG members considered that it might be possible to produce such a device at a cost that, combined with the potential safety benefits, could encourage a significant proportion of the GA community to adopt it voluntarily. The ECWG therefore recommended that a project be initiated to take the development of such a standard forward.” (CAP 1391, CAA UK, April 2018)

EC solutions have been put forward for full adoption by CAA UK due to the following benefits (CAP1777):

  1. To maintain and enhance safety by mitigating the risk of airspace infringement and mid-air collisions
  2. To improve efficiency by seeking to offer airspace users access to the airspace they require to conduct their operations most effectively
  3. To act as a critical enabler for the integration of UAS by establishing a comprehensive foundation of EC that UAS operators can rely on to detect and avoid other airspace users remotely or automatically using connected technologies

In order to fully embody the above-mentioned benefits, CAP1777 states that full adoption of EC solutions should be based on the following four principles:

  1. User focused: putting airspace users, passengers and businesses that rely on aviation at the centre of the approach.
  2. Evidence led: targeting our activity to solve specific problems and deliver tangible benefits and avoiding activity that does not address a need
  3. Market-driven: focusing on the enablers required to help the market for EC solutions to work effectively
  4. Interoperable: focusing on the functions that EC solutions should provide to ensure interoperable connectivity

It was further suggested in the CAP1777 that the EC solutions should be deployed in three functionality levels, which not only comply with but further move beyond the current “See and Being Seen” principle:

Level 1 (Transmit only):

“All airspace users operating in the designated block of airspace must transmit their location and altitude using an interoperable EC solution. ATS units and UTM providers can invest voluntarily in interoperable ground-based solutions as they require”

Level 2 (Transmit and receive):

“All airspace users operating in the designated block of airspace must transmit and receive location and altitude information to/from all other airspace users using interoperable EC solutions; and, all ATS and UTM providers operating in the designated block of airspace must receive location and altitude information from airspace users using an interoperable ground-based solution”

Level 3 (Transmit, receive and rebroadcast):

“ATS and UTM providers must receive EC information and must rebroadcast the information to all other operators, potentially with ‘value-add’ services like weather information or routeing options”

2.5 Electronic Conspicuity in ATMS: How does EC affect ATC operations?

There is no denying that EC solutions could enhance the margin of safety for VFR traffic. Nonetheless, its effect brought to normal ATC operations must be thoroughly considered before implementation and integration of any EC signals to ATMS. Topics brought up in the following should not be considered exhaustive but provide a basis for future in-depth research and discussion.

  1. Minimise effect from human errors in reporting aircraft position verbally. Instead each aircraft could be displayed electronically on both cockpit and ATS surveillance systems which would result in improved situation awareness for pilots and controllers.
  2. Provide an extra safety net apart from “See and Avoid” concept for pilots of VFR traffic.
  3. Extra liabilities and duty of care for controllers might be generated after integrating the EC signals into existing ATMS to prevent collision between aircraft. Guideline to use the flight data displayed from EC solutions on ATMS must be defined to protect controllers. Rules and regulations in regard to handling traffic displayed from EC solutions must be clearly promulgated.
  4. Early detection of possible airspace infringement: this could be achieved through integrating EC signal into ATMS and generate warnings to controllers when there is possible airspace infringement.
  5. Surveillance system workload: Extra processing power is required to process electronic information from EC participating aircraft that transmit their electronic conspicuity data.
  6. Screen cluttering: Additional workload is created for ATCOs having to monitor and process additional aircraft position and intent information. Even though it is just a target symbol, it will occupy controllers’ capacity in registering the information in the mental traffic picture. A flexible tuning, filtering and parameterisation of data displayed to controllers with suitable safety nets must be available at controller working position, so as to reduce screen cluttering and display useful information only. The filter options should suit the need as required in different block of airspace.
  1. Expectation mismatch between pilot and controllers: Currently there is no published guidelines by ICAO, if EC information is displayed on ATMS how the, information might be utilized and interpreted. This, as suggested in the IFATCA TPM LM 11.2.7, might generate a difference in the expected level of service between pilot and controller.
  2. Integrity of EC signal: There is no guarantee on the integrity of EC signal since “EC devices use limited capability, low complexity, off-the-shelf components that do not meet classical aviation equipment requirements” (CAP 1391, CAA UK, April 2018).

Extreme caution must be exercised when integrating EC signal into ATMS system.

2.6 IFATCA Policy on Electronic Conspicuity (EC) Solutions

Currently there is no dedicated policy from IFATCA on EC solutions. Given the fact that EC solution is still evolving at its early stage, a policy draft from IFATCA on this subject may not be future proof and hence is not being recommended. Nevertheless, existing policies in the Technical and Professional Manual (TPM) could be referred to when adopting the EC solutions:

IFATCA TPM 2019 edition, WC 8.2.8 Regulatory Approval of ATM Systems Equipment, Page 197:

Any information displayed at a controller working position shall be approved to be used operationally


That means the information/ data displayed at controller working position has been vetted and carefully considered by management to be used by controllers. This may address the concern regarding the extra liabilities given to controllers when incorporating EC signals into ATMS. They may also ensure the integrity of EC signal to be displayed when integrating any EC solutions into ATMS.

IFATCA TPM 2019 edition, AAS 1.2 Automatic Dependent Surveillance (ADS), Page 56:

When use of ADS-B signal was adopted as the EC solution, IFATCA policy on ADS could be referred to:

“… only pertinent and useful flight data should be supplied to the control team, which supports and enhances the building of human mental models and controllers situation awareness…”

“…The separation standards to be applied between ADS positions and all other surveillance targets must be subjected to an ICAO approved collision risk analysis…”

“… Displays of ADS information that are presented to the controller should be designed to that they meet the need of the control task and enhance the usability of the system…”


These policies would not only address the concern of bringing extra liabilities to controllers, but also the screen cluttering problem that would be brought up on controllers working position when adopting the EC solutions from ADS-B signal.

IFATCA TPM 2019 edition, AAS 1.13 Determining Operations Readiness of New ATM Systems, Page 71:

To ensure the integration of EC solutions into ATMS would deliver the expected benefits to ATC as stated in the last section, TPM AAS 1.13 could be referred to:

“Operational controllers shall be involved in the design, development and implementation of new ATM systems. Their role shall include:

  • establishing user requirements
  • defining operational training requirements prior to implementation
  • participating in the risk assessment process
  • validating the system
  • providing feedback in the future development of the system”


2.7 Use of EC solutions

Current IFATCA policy regarding “Use of ATS surveillance data in the provision of non-surveillance services” points out that:

“Where ATS Surveillance Data is provided to assist in the provision of an Air Traffic Service, rules on the use, restrictions and limitations of the surveillance data shall be published, so that legal responsibilities are clear and unambiguous. Controllers who are required to use surveillance data shall be provided with suitable training in ATS Surveillance Systems.”

 (IFATCA TPM 2019 Edition, LM 11.2.7 Use of ATS Surveillance Data in The Provision of Non- Surveillance Services, Page 318)

ICAO Doc 9924 – Aeronautical Surveillance Manual (first edition, first amendment, applicability date 5 April 2012) defines the functions of aeronautical surveillance system as follows:

“provides the aircraft position and other related information to ATM and/or airborne users. In most cases, an aeronautical surveillance system provides its user with knowledge of “who” is “where” and “when”.”

Broadly speaking EC systems could be defined as aeronautical surveillance system and use of EC data should be in compliant with the above policy. Hence, prior to full adoption and integration of EC with existing ATMS, in-depth studies in the following aspects should be carried out:

  1. How will EC minimise human error from ATC
  2. How will EC provide extra safety net for ATC and airspace users in daily operations, e.g. early detection of airspace infringement
  3. What are the extra liabilities and duty of care added to ATCO after adopting the EC
  4. How will EC affect ATC daily operations, in terms of screen cluttering, separation standard, flight data signal integrity etc.
  5. How will EC affect the expectation of level of services provided by ATC to pilot


3.1  EC is a concept that can be used by the pilot to have an improved situational awareness. Improvement of conspicuity of aircraft provides a more complete safety net to airspace users.

3.2  Although EC solutions are available in the market in various systems, they are not interoperable and incompatible. A unified standard on EC solutions is needed should it be adopted and integrated with existing ATMS.

3.3  Prior to the full adoption of EC in ATMS, in-depth studies on how EC affects ATC operations should be carried out. These may not only require input from ATC and pilot communities, but also local authorities, ANSPs, and even the EC solutions providers.


4.1 It is recommended that this paper is accepted as information material.


IFATCA Technical and Professional Manual Version 64.0 – July 2019.

CAP1391 – Electronic Conspicuity Devices, Civil Aviation Authority UK, April 2018.

CAP1777 – Airspace Modernisation Strategy: Electronic Conspicuity Solution, A calls or evidence on a new strategy, Civil Aviation Authority UK, March 2019.

ICAO Doc 9924 Aeronautical Surveillance Manual, first edition, first amendment, applicability date 5 April 2012.

ICAO Doc 4444 Air Traffic Management, sixteenth edition, applicability date 10 November 2016.

Safety Sense Leaflet 13 – Collision Avoidance, Civil Aviation Authority UK, January 2013.

Airproxes and Collisions of Aircraft in German Airspace (BFU 803.1-17), German Federal Bureau of Aircraft Accident Investigation, January 2017.

Final report BEKLAS – Recognizability of gliders and small motorised aircraft, Federal Ministry of Transport and Urban Affairs of Germany, May 2004.

Regulation 14 CFR Part 91.113 (b), Federal Aviation Administration (FAA).

Life or Death in 250 Milliseconds by Major Michael T. Lippert, U.S. Marine Corps, Proceedings Vol. 143/1/1367, U.S. Naval Institute, January 2017.

Advisory Circular AC No. AC 90-48D by Federal Aviation Administration, US Department of Transportation.

Last Update: October 2, 2020  

July 18, 2020   507   Jean-Francois Lepage    2020    

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