Technology has created the possibility to provide aerodrome control service from a location other than the aerodrome itself. This new concept is being developed both in SESAR and NEXTGEN and is also studied in other countries such as Australia. This document studies the factors behind the interest in remote towers as well as the potential advantages and areas of concern. New policy is proposed in this paper.

1.1 The Remote Towers Concept has seen significant global development over recent years, with a number of ANSPs collaborating with system providers to evaluate and begin implementation of remote tower systems.

1.2. There are two core identifiable drivers for implementation of Remote and Virtual Towers. These can be broadly defined as ‘cost reduction’ and ‘service enhancement’.

1.3 RVT is included in the European SESAR and United States’ NextGEN programs, and programs are underway in other countries such as Australia.

2.1 Definition

Remote Tower – provision of an aerodrome control service from a location other than the aerodrome at which the service is being provided.

2.1.1 Acronyms currently in regular use referring to Remote towers are:

• RVT – Remote and Virtual Towers,
• RTC – Remote Tower Concept/Remote Tower Centre.

For consistency, and to avoid confusion between Remote Tower Concept and Centre, this paper will refer to RVT.

2.2 Motivators behind implementation

2.2.1  A number of factors are combining to motivate industry to push the concept of RVT, including cost reduction/rationalisation, resource centralisation, service enhancement and availability of new technologies.

2.2.2  ANSPs and airspace users alike are continually seeking to rationalise costs. It is hoped by ANSPs that RVT can contribute to reduced costs by reducing both capital infrastructure, and staff related costs.

2.2.3  Resource centralisation is regularly touted by ANSPs as a driver of reduced costs, improved efficiency and standardisation of procedures. RVT is attractive in this sense, as it could allow centralisation & consolidation of ATCOs involved in the provision of tower services.

2.2.4  Provision of control services at remotely located aerodromes is sometimes considered by ANSPs to be ‘impractical’ or not ‘cost-effective’, due to the costs associated with basing permanent staff in such locations and construction and maintenance of tower facilities. In some circumstances RVT may allow reduced capital and staffing costs associated with the establishment of such services.

2.2.5  The aviation regulatory environment in some countries stipulates that ATC services must be provided to all Regular Public Transport (RPT) flights. This results in ATC tower installations being built in remote areas to service very few movements. In these cases the ANSP may see potential for cost savings while continuing to provide the required level of service with RVT.

2.2.6  Integration of technologies such as ADS-B, Pan Tilt Zoom (PTZ) cameras and A- SMGCS could in theory provide enhanced situational awareness for ATCOs in a way that isn’t practicable in a traditional tower (eg: radar tags and on screen alerts).

2.3 Technology

2.3.1  A camera installation is constructed at the aerodrome. The installation includes multiple high definition cameras to provide up to 360 degree vision, Pan, Tilt, Zoom (PTZ) cameras for individual aircraft/object tracking, microphones and potentially infrared cameras and ADS-B receivers.

2.3.2  The data is compressed and transmitted to the remote tower centre, where it is decompressed and converted for display to the ATCO in the virtual tower.

2.4 Development so far

2.4.1  Development and planning of RVT and similar concepts is underway in the two major ATM modernisation programs globally: SESAR and NextGEN.

2.4.2  The NextGEN initiative has been called ‘Blended Airspace’ and aims to utilise technologies to allow controllers to provide surface separation remotely from a centre or TRACON, with final recommendations on the program expected by late 2014.

2.4.3  ‘Remote and Virtual towers’ are listed as items in SESAR workpackage WP6 – ‘Airport Operations’, and WP12 – ‘Airport Systems’.

2.4.4  A number of suppliers are developing RVT products, and can be expected to compete vigorously for ANSP contracts to implement RVT.

2.4.5  ICAO is assessing the concept with regard to the need to update ICAO provisions, and it is included in ASBU module B1-81. The following recommendations are found in a working paper from ANC 2012 presented by European Union and its Member States; by the other Members States of the European Civil Aviation Conference; and by EUROCONTROL)

b) Request ICAO to urgently initiate the necessary actions to update ICAO provisions to provide for:

1) Requirements for the use of sensors, and display technologies to replace visual observation of traffic in the provision of Air Traffic Control and Flight Information Services;

2) Additional requirements for surveillance and ground/ground communications systems to adapt to the above;

3) New operational procedures, where relevant, both at the remote ATC facility and on the airborne side; and

4) New requirements for ATCO/pilot training and eventually licencing if necessary.

2.5 Potential advantages of the technology

2.5.1  Remote towers may allow for provision of aerodrome control services at locations where it is currently impractical. The potential for reduced infrastructure costs and lead times for establishment of a service may also allow for the temporary establishment of services where there is a medium term need.

2.5.2  Advanced camera technology, including PTZ (Pan, Tilt, Zoom) and infrared, could provide a high level of visibility and fidelity, as well as enhanced situational awareness in low visibility conditions (fog, low cloud, precipitation etc…).

2.5.3  Integration of surveillance technologies directly into the screen display (eg. Radar, ADS- B, A-SMGCS etc…).

2.5.4  Automation assistance routine control practices & techniques, for example- automated runway scan with PTZ cameras.

2.5.5  Object detection may assist in detecting and preventing violation of controlled airspace (VCA). Automated detection of hazards such as birds or foreign objects on runways may assist ATCOs to provide hazard alerting.

2.5.6  RVT systems could be installed at major airports for use in contingency situations. Although a contingency RVT may not be able to provide the same level of service as the existing conventional tower, an airport could continue to operate safely at reduced capacity until the contingency is resolved.

2.6 Areas of concern

2.6.1  Aerodrome control is a critical ATC service, and as such must have a very high level of reliability and redundancy. Ultimate fall backs that exist in traditional towers such as ALDIS signal lamps and handheld transceivers will not be available.

2.6.2  While integration of surveillance technologies and alerts into the screen display provides an opportunity to enhance situational awareness, if not implemented appropriately, it might pose the risk of information overload or ‘alarm fatigue’ for controllers. Nuisance alerts can create unacceptable distractions for ATCOs. In complex task environments such as ATC, research has shown false alarms to lead to less frequent and slower alarm responses (Bliss, Dunn & Fuller 1995).

2.6.3  Automation can lead to a tendency of over reliance on the correct functioning of the system to maintain situational awareness. In a highly automated system it is essential that fundamental controller skills and knowledge are maintained through regular training in degraded operations.

2.6.4  Poorly implemented alerts and corresponding procedures can lead to ambiguity in controller/pilot responsibilities. The provision of safety net alerting in automated en-route environments is well established, and it is known that safety net alerts require specific and unambiguous procedures for assessment and response to the alert. Ambiguity in the procedure or responsibility for alert response can lead to inappropriate action or lack of action.

2.6.5  A 2004 Australian Transport Safety Bureau investigation into a Controlled Flight Into Terrain (CFIT) accident at Benalla aerodrome in Australia found that ‘instructions to controllers relating to Route Adherence Monitor (RAM) alerts could be ambiguous’. Controllers had received a RAM alert, however due to uncertainty over pilot intentions and procedures for RAM response, did not query the pilot. In this particular case clear and unambiguous procedures would likely have averted the accident. Although from the enroute environment, this example demonstrates the importance of properly implemented alerts in an ATM system.

2.6.6  ANSPs may wish to provide benefits of technologies before they are ready to be fully implemented, resulting in data provided to ATCOs that can be used for ‘information only’. The provision of information to ATCOs that cannot be fully used to make operational decisions creates liability concerns, due to duty of care issues and lack of clarity over the circumstances under which ATCOs are able to use the information operationally.

2.7 Control Practices and Separation

2.7.1  Regardless of the levels of quality and reliability of RVT, they will not be the ‘same’ as traditional towers. Conventional control towers are able to utilise reduced separations in the vicinity of an aerodrome. This is in part due to their simplicity. All that is required is a functioning radio, there is no latency and they have multiple redundancy. RVT have more potential points of failure and may not be able not be relied on to the same degree. Existing methods of separation will need to be reviewed and assessed with regards to their suitability for use with RVT.

2.7.2  Specific separation standards for RVT should be devised through a scientific process taking into account all factors relevant to the RVT operational environment, including but not limited to – system latency, visual performance/resolution, effect of visual compression. At the time of writing, there are no specific RVT standards approved at the ICAO or national regulator level.

2.7.3  Although RVT are intended to provide as accurate a representation as possible of a control tower view, ultimately, the camera technology is a form of electronic surveillance, not direct visual observation. Existing visual control practices and separation standards cannot simply be transplanted into RVT operations without undergoing rigorous assessment of their suitability for RVT.

2.7.4  IFATCA defines visual observation as:

2.7.5 IFATCA policy on visual observation remains valid. RVT sensor and display technologies should be considered a means of surveillance, rather than visual observation, and required performance standards defined accordingly.

2.8 System Performance and equipment

2.8.1  There is no specific ICAO requirement for the minimum level of equipment required for provision of an aerodrome control service, for either a manned tower or RVT. Furthermore, there is no defined ICAO method or rating for specifying the actual level of sensor or system performance of RVT.

2.8.2  The concepts of Required Navigation Performance (RNP), Required Communication Performance (RCP) and Required Surveillance Performance (RSP) exist in order to be able to categorise the capabilities of an aircraft or ground system for the purpose of determining appropriate level of service.

2.8.3  A framework or concept for measuring and categorizing the performance of RVT, with particular reference to the video technology, may be required for determining the level of service able to be provided from a specific system. As RVT will be implemented with different specification levels around the world, there will also be differing capabilities. Development of a ‘Required Visual Performance (RVP)’ concept, or including RVT sensor performance standards in RSP, could be given consideration to determine the performance and appropriate service levels from specific RVT installations.

2.9 Human Factors and Performance

2.9.1  There will be a number of differences between traditional towers and remote towers in the area of human factors. These may include, but are not limited to, eye strain and fatigue, low light and night conditions, depth perception.

2.9.2  It is well established that prolonged use of screens leads to eye fatigue and eyestrain. This can be exacerbated by sub-optimal lighting, and factors such as screen flicker, screen refresh rates, and resolution. Continuous noise from cooling fans, and dry air from air conditioners can also have a fatiguing effect. ATCOs who have experience working in advanced tower simulators frequently report that they are unable to work for prolonged periods due to eye fatigue and strain caused by electronic displays.

2.9.3  Remote tower installations need to be rigorously assessed with regards to the above, and ATCO shift lengths and break requirements set accordingly. It may be the case that ATCO shift lengths need to be shorter, and required breaks longer and at more regular intervals, than for a traditional tower.

2.9.4  Night and low light operations pose a similar issue. ATCOs assessing trial RVTs have reported reduced screen resolution, pixelation, as well as difficulty distinguishing between runway, taxiway and off-airport lights during night hours. Additionally, it has been reported by some ATCOs involved in trial assessments that judging distance visually is generally more difficult than in a traditional tower.

2.9.5 Eurocontrol/NORACON Human Performance study on Virtual Towers recommends:

‘Conduct a fatigue study to determine the shift schedules and required breaks / rest periods’

due to the risk of increased fatigue in the context of reduced daylight and screens. IFATCA supports efforts to conduct appropriate studies into human factors requirements with regards to RVT.

2.10 Multiple endorsements

2.10.1  ANSPs and ATM suppliers have widely promoted the benefits of consolidating tower ATCO staffing into central locations. It is inevitable that with RVT technology, ANSPs will seek to establish centres (RTC) where numerous aerodromes are controlled from a single facility. This will likely result in tower controllers being expected to hold endorsements for multiple aerodromes.

2.10.2  There are existing examples where ATCOs concurrently hold endorsements for more than one aerodrome, however it is unlikely that more than one of these would be exercised in a single shift, as the aerodromes would be in different locations.

2.10.3  In situations where controllers are expected to maintain and exercise multiple endorsements, training (including refresher training), rest breaks, HMI design and other relevant factors must be taken into account to ensure controller competency. It may be necessary to align procedures at airports where controllers are expected to hold multiple endorsements, such as renaming taxiways and visual reporting points and aligning alarm plans and Letters of Agreements between the ANSP and the aerodrome operator and approach control.

2.10.4  Stated plans by some ANSPs for ATCOs to operate more than one tower simultaneously are of significant concern. The potential for sudden unexpected peaks in workload and loss of situational awareness could lead to a significant reduction in ability to provide safe ATS, including during expected periods of low traffic.

2.10.5  The concept of operating multiple towers simultaneously differs greatly from the enroute or approach environment, where there are numerous examples of controllers performing different control functions (eg. enroute combined with approach, or operating numerous enroute sectors). Generally when enroute and approach functions are combined, it will be a contiguous and coherent volume of airspace, allowing the controller to develop a single mental model of the situation. Operating multiple towers would result in a fragmented situational awareness, and there is potential for significant differences in factors such as weather between the aerodromes.

2.10.6  Instead of operating several aerodrome simultaneously, it might be possible to reduce costs by co-locating an RTC next to a TRACON or ACC and work tower and approach as a common rating and by the same body of controllers, combining TWR and APP functions at times of low traffic.

2.11 Weather

2.11.1  Full meteorological observation (METOBS) may not be able to be performed by ATCOs operating remote towers. The function may need to be delegated to an accredited person on the aerodrome site, such as airport fire service personnel or the aerodrome operator. In some countries, this function is already performed by someone other than an ATCO, such as the aerodrome operator, particularly at uncontrolled aerodromes. At major airports, this function is often performed by dedicated meteorological personnel.

2.11.2  ATCOs may lose intimate local knowledge of weather patterns due to being located off- site, particularly where ATCOs regularly work more than one aerodrome from a remote facility. This could affect critical decision making and situational awareness where it relates to weather.

2.12 Reliability & Redundancy

2.12.1  Aerodrome control is a critical service, as remote towers will require an exceptionally high level of reliability and redundancy.

2.12.2  ATCOs using the system must have a high level of confidence in its reliability. Benefits of new technology may be partly negated if ATCOs don’t trust the system, reducing any efficiency benefits if ATCOs revert to procedural or conservative techniques.

2.12.3  Alerts and warnings for controllers will be necessary to alert them immediately to system failure or degradation, including latency issues, screen freezing, and camera and other failures.

2.12.4  Manned towers generally have 2 levels of communication redundancy (secondary and tertiary equipment – ie: handheld). Handheld transceivers are not possible in a remote tower, so another form of tertiary redundancy should be devised.

2.12.5  Camera installations must be able to be cleaned regularly and at short notice. A number of factors such as condensation, raindrops, bird droppings or nesting and dust could impair visibility or damage camera installations.

2.12.6  Where multiple aerodromes are controlled from a single centre, a system failure or building evacuation could cause multiple aerodromes to lose ATC service. It could be the case that an aircraft’s destination, as well as suitable alternates, become unavailable with little or no notice. Contingency procedures must be available for provision of appropriate levels of ATS in such circumstances.

2.13 Existing IFATCA policy

3.1  The remote and virtual tower concept is fast becoming a reality, and it is likely that fully functional examples will be operational in some parts of the world in the near future. Implementation is being driven by a combination of motivating factors, including but not limited to, cost reduction/rationalisation, resource centralisation, service enhancement and availability of new technologies.

3.2  The technology provides opportunities to provide services where it is currently impractical, provide contingency services at airports where manned towers exist, and integrate new technologies into tower control.

3.3  For RVT to be implemented safely and successfully, it is essential that ATCOs are involved in all stages of development and implementation.

3.4  Areas that are yet to be fully addressed by ICAO and national regulators include:

• Performance requirements for the use of sensors (including cameras) and displays to replace visual observation.
• Operational procedures for both controllers and pilots.
• Requirements for ATCO training, licensing and controller working conditions.

3.5  RVT cameras and sensor technologies should be considered to be a form of surveillance, and system and sensor performance criteria specific to RVT technologies should be established.

It is recommended that;

4.1  IFATCA Policy is:

ATCOs shall not be expected to provide a Remote and Virtual tower service for more than one aerodrome simultaneously.

and is included in the IFATCA Technical and Professional Manual.

4.2  IFATCA Policy is:

Separation standards and procedures for Remote and Virtual Towers shall be developed or adapted and implemented based on a robust safety case and the demonstrated capabilities of the system.

and is included in the IFATCA Technical and Professional Manual.

4.3  IFATCA Policy is:

ICAO should develop required performance standards for Remote and Virtual Tower systems and sensors.

and is included in the IFATCA Technical and Professional Manual.

Eurocontrol/NORACON Human Performance Study.

IFATCA Technical and Professional Manual.

Reversal of the Cry-Wolf effect: An investigation of two methods to increase alarm response rates (J. Bliss, M. Dunn, B.S. Fuller, 1995).