Study the Virtual Tower Concept

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Study the Virtual Tower Concept

45TH ANNUAL CONFERENCE, Kaohsiung, Taiwan, 27-31 March 2006

WP No. 90

Study the Virtual Tower Concept

Presented by TOC


1.1.  This work study is related to the “Remote Aerodrome Control Concepts” paper presented in Melbourne last year.

1.2.  This paper investigates Virtual Tower concepts based on the presentation of the Swedish Member Association (MA) in Melbourne 05. This presentation introduced a Virtual Tower concept developed by the Swedish Air Navigation Service Provider (ANSP).

1.3.  When reference is made to the “Remote Tower Concept”, then the German Remote Tower Concept is that to which it is referred. That concept is further expanded on under agenda item C.5.9.


2.1. Virtual Tower Concept as introduced by the Swedish ANSP

This concept aims for small aerodromes with little IFR traffic. The basic concept includes a camera mast to be located at an optimum location at the airport. The cameras shall provide a sharp and stable picture even under strong wind conditions and will be infrared capable. Cameras shall also be vertically adjustable to select optimum view with regard to visibility and clouds.

A traditional tower cab is built on ground. Live pictures are displayed on the virtual windows. The view is comparable to a real tower. A dome may be used to display traffic overhead. This virtual tower cab does not have to be located at the airport. An aerodrome control centre with more than one virtual cab may be possible.

In addition to the cameras the following systems may be installed to enhance situational awareness: Radar, Surface Movement Radar (SMR), Automatic Dependent Surveillance Broadcast (ADS-B), heat sensors, microphones.

2.2. Comparing basic ideas of “Virtual Towers” and “Remote Towers”

2.3. Technical and operational aspects

2.3.1. Like in the concept for remote towers these plans appear to give less priority to visual observation. Unlike the “remote tower” concepts, “virtual towers” are planned to be supplied with compensatory devices to replace direct eyesight through cameras.

Still cameras even when using the most advanced techniques currently available cannot replace the three dimensional view from a human eye. Distances are hard to estimate in particular when the provided picture on the screen shows a perfectly sharp image.

ICAO provisions demand for visual observation, but unfortunately still leave some space for (mis)interpretation. Therefore, TOC suggests the drafting of a clear definition for the term “visual observation” highlighting the ability of the human eye to focus on particular objects rather than on the whole picture and to obtain a three dimensional impression of space rather than a surface (plane). Human eyesight may be supported by devices that do not affect the above mentioned advantages (glasses, binocular).

2.4. Relevant ICAO provisions

2.4.1.  Annex 11:


Aerodrome control tower. A unit established to provide air traffic control service at aerodrome traffic.

3.2 The parts of air traffic control service described in 2.3.1 shall be provided by the various units as follows:

c) Aerodrome control service: by an aerodrome control tower.

2.4.2.  PANS ATM Doc 4444:

4.3.1 Aerodrome control service

Aerodrome control service shall be provided by an aerodrome control tower. Aerodrome controllers shall maintain a continuous watch on all flight operations on and in the vicinity of an aerodrome as well as vehicles and personnel on the manoeuvring area. Watch shall be maintained by visual observation, augmented in low visibility conditions by radar when available. Traffic shall be controlled in accordance with the procedures set forth herein and all applicable traffic rules specified by the appropriate ATS authority. If there are other aerodromes within the control zone, traffic at all aerodromes within such a zone shall be coordinated so that traffic circuits do not conflict.

Obstructed runway

In the event the aerodrome controller observes, after a take-off clearance or a landing clearance has been issued, any obstruction on the runway likely to impair the safety of an aircraft taking off or landing, such as runway incursion by an aircraft or vehicle, or animals or flock of birds on the runway, appropriate action shall be taken as follows:

a) in all cases inform the aircraft concerned of the obstruction and its location on the runway

b) cancel the take-off clearance for an aircraft which has not started to roll

c) instruct a landing aircraft to go around Whenever an abnormal configuration or condition of an aircraft, including conditions such as landing gear not extended, or unusual smoke emissions from any part of the aircraft, is observed by or reported to the aerodrome controller, the aircraft concerned shall be advised without delay.

7.4.4 When a not previously notified condition pertaining to the safe use by aircraft of the manoeuvring area is reported to or observed by the controller, the appropriate aerodrome authority shall be informed an operations on that part of the manoeuvring area terminated until otherwise advised by the appropriate aerodrome authority. SMR should be used to augment visual observation of traffic on the manoeuvring area and to provide surveillance of traffic of the manoeuvring area which cannot be observed visually.

2.4.3.  Annex 14: A signalling lamp shall be provided at a controlled aerodrome in the control tower.

2.4.4.  Doc 9426:

Part 3, Section 2, Chapter 2 Specific requirements for an Aerodrome Control Tower. …

2.1.2 Surveillance by the aerodrome controller is normally done by visual means (eyesight) alone, mechanically through the use of binoculars to improve eyesight or electronically, through the use of radar or closed-circuit television….

2.1.3 The height of the tower should be such that, at normal eye level (about 1,5m above the floor of the tower cab) the controller is provided with the visual surveillance previously described…


3.1.  Air Traffic Control is a task based on observation. In order to keep safety and efficiency on the maximum level it is necessary to provide air traffic controllers with the optimum devices to maintain the level of service. Visual observation is an important tool for aerodrome control and shall be guaranteed whenever weather allows. To remove this important tool will certainly decrease the quality of the service provided, and might affect the level of safety in a negative way as well.

3.2.  For the above mentioned reasons this concept is not acceptable for IFATCA. It is clearly contradictory to many of the quoted ICAO provisions. Where there is no obvious contradiction, ICAO paragraphs leave space for interpretation in a direction, which serves economical reasons more than safety aspects. This is unacceptable by IFATCA. Hence, IFATCA should suggest changes to the relevant phrases.

3.3.  For the time being no concept has been introduced that is acceptable to IFATCA. IFATCA does not support any future ATM concept for the provision of Aerodrome Control Service, unless the following requirements are met:

  • Aerodrome controllers have to be provided with the same or better quality of surveillance as achieved by visual observation, in particular in regard to the three-dimensional view of direct eye-sight;
  • In addition to standard fallback procedures for Aerodrome control towers proper fall back procedures must be implemented in case of failure of any technical device influencing the situational awareness of tower ATCOs; and
  • A full safety assessment must be made before implementing such a new concept.


It is recommended that;

4.1  IFATCA Provisional Policy is:

Whenever ICAO uses the term “visual observation”, IFATCA considers this to be direct visual observation

and is included in the IFATCA Manual on page 3 2 2 2.

4.2  IFATCA Provisional Policy is that Direct visual observation is defined as:

Observation through direct eyesight, not supported by means other than optical aids (glasses/lenses) that correct vision.

and is included in the IFATCA Manual on page 3 2 2 2.

4.3  IFATCA Provisional Policy is:

An aerodrome control unit is a unit established to provide air traffic control service to aerodrome traffic. It shall provide aerodrome controllers the capability to maintain a continuous watch on all flight operations on and in the vicinity of an aerodrome as well as vehicles and personnel on the manoeuvring area. This watch shall be maintained by direct visual observation, possibly augmented by other means.

and is included in the IFATCA Manual on page 3 2 2 2.

4.4  IFATCA Provisional Policy is:

Any future ATM concept for the provision of Aerodrome Control Service, is only acceptable to IFATCA, provided that;

  • When direct visual observation is replaced by alternative means, it must be as good as, or better than direct visual observation; and
  • In addition to standard fall back procedures for Aerodrome control units, appropriate fall back procedures must be implemented in case of failure of any technical device influencing the situational awareness of aerodrome controllers.

and is included in the IFATCA Manual on page 3 2 2 2.

Last Update: September 29, 2020  

March 29, 2020   740   Jean-Francois Lepage    2006    

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