Investigate the Use of Cockpit Display of Traffic Information (CDTI) with Enhanced Surface Movement Guidance Control Systems (SMGCS)

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Investigate the Use of Cockpit Display of Traffic Information (CDTI) with Enhanced Surface Movement Guidance Control Systems (SMGCS)

38TH ANNUAL CONFERENCE, Santiago, Chile, 15-19 March 1999

WP No. 87

Investigate the Use of Cockpit Display of Traffic Information (CDTI) with Enhanced Surface Movement Guidance Control Systems (SMGCS)


The term Cockpit Display of Traffic Information (CDTI) refers to a generic avionics device in an aircraft cockpit, that is capable of displaying position information of nearby aircraft. It may also include display of ground reference points and navigation information to increase the pilot’s situational awareness.

The display is the interface between the data processing and the pilot. Required display elements, their quality and the specific information presented may vary based on the intended operational use of CDTI.
In today’s environment, a remarkable contrast exists between airborne and ground aircraft operations. While modern aircraft are capable of flying their routes automatically to great accuracy and at minimised fuel consumption under almost any weather condition, during taxi operations the crew is forced to control the aircraft manually, navigate with paper charts and maintain traffic awareness on the surface by way of frequent visual scans and, in some cases, radio communications with ATC to obtain traffic advisories. Especially on large airports with a considerable runway/taxiway complexity and high-workload situations, flight crews often have problems to understand and comply with the cleared taxi routes. Furthermore, as visibility conditions deteriorate, at night, or under high workload conditions, maintaining awareness of traffic and own position within the airport can become difficult. In these types of situations, uncertainties could arise that, in the best case, reduce flow rates, and in the worst case, increase the likelihood of a runway incursion and/or ground accident.

The annual accident statistics indicate a large number of accidents due to disorientation on the ground and the worst accident in aviation history occurred due to a runway transgression at Tenerife, Canary Islands.

The aim of this paper is to investigate if CDTI might be considered capable to support applications to enhance the overall ground system capacity and to examine the operational issues and operating constraints consistent with its findings. If certain specific additional uses of CDTI are found to be viable and useful, it would be appropriate to address the issues regarding the definition of responsibility allocation, operating rules, training and procedures to harness such benefits.


ICAO has drafted the operational requirements for Advanced Surface Movement Guidance and Control Systems (A-SMGCS). A-SMGCS requirements were written to support the safe, orderly and expeditious surface operations under all circumstances and various visibility conditions. Furthermore, RTCA has drafted Minimum Aviation System Performance Standards (MASPS) for airport surface navigation. Both these documents contain requirements that imply the use of CDTI for some operations.

For example, ICAO suggests the following pilots requirements to support A-SMGCS operations down to zero visibility:

  • tactical and strategic planning information that indicate the current traffic situation and the predicted traffic situation in advance;
  • information on current location and direction at all times;
  • information that indicates spacing from preceding aircraft;
  • information that indicates spacing from other aircraft, vehicles, and obstacles, in some visibility conditions;
  • indication of the required sequencing;
  • information to prevent jet blast effects;
  • identification of areas to be avoided;
  • information to prevent collision with other aircraft, vehicles, or obstacles;
  • alerts to prevent incursions onto runways and taxiways.

Assuming that appropriate air-ground data communication capacity is provided, a first application to be considered is the integration of ground data to airborne CDTI. In this way, CDTI should provide a situation–dependent display of the airport, own aircraft position, assigned taxi route and positions of other co-operating aircraft/vehicles. Such information should be primarily used by “non-steering” crewmember so that “pilot” can maintain eyes-out to perform “see and avoid”.

CDTI should provide the necessary functions to permit the crew to comply with the ATC instructions in Low Visibility Operations (LVO) as well. Furthermore, in case of a deviation occurs, the CDTI should provide an appropriate warning, especially in case of runway incursion and/or conflict detection. Ground data should be received by a capable and robust data-link system, as well as clearances, planning times, aircraft/vehicles positions, identification, intentions and status.

In particular, the surveillance data could be derived from several possible sources (e.g.: ADS-B, Mode S etc.). The data fusion for the purposes of traffic data correlation should be done by a ground-based surveillance function independent from CDTI. In this way, the surveillance function will be able to ensure the needed airborne/ground data coherency.

With respect to implementation of ADS-B surveillance function, it is important to note that it is unlikely that all aircraft will be equipped with ADS-B capability in the near term. In a mixed environment, crews must be aware of the fact that non-equipped or non-co-operating (transponder off) aircraft/vehicles will not be presented on the CDTI. In general, the CDTI should offer the following main functionality to support enhanced situational awareness during airport LVO:

Display on a moving airport map with traffic positions (Lat/Long or bearing/distance) and related identity and FOM (Figure Of Merit), RWYs, TWYs, parking positions, and relevant buildings; Several zoom levels:

  • Display of the cleared taxi route;
  • Defined colour/symbol codes according to specific RWYs, TWYs and traffic status;
  • Display of the planning data generated by ground ATC system;
  • Display of warnings in case of runway incursion, loss of in-trail separation, deviation from the cleared taxi route and potential conflict detection (head-to-head and intersecting paths).

In this context, CDTI availability during airport operations could provide flight crews with increased situational awareness while decreasing uncertainties associated with available visual cues and radio communications.

This increased awareness could reduce the likelihood of:

  • runway incursions and surface accidents;
  • navigation errors on the surface;
  • reduce the amount of radio communications required during the airport operations.

Frequently, ATC ground guidance function is provided to flight crews relative to other traffic/vehicles. For example, “ANA 601, follow company traffic” or “DAL 833, follow the 737 on your left”.

A ground CDTI capability should support adherence to these types of instructions in low visibility operations. So, CDTI capability could be critical in enabling, weather-independently, a safe and efficient high capacity flow rates on the airport ATC operations during Low Visibility Operations (LVO).

CDTI could enable, during low visibility operations, tighter separations on the surface and higher taxi speeds and traffic flow.

Simulations and field tests at NASA have shown that CDTI (along with the display of an airport moving-map, route, and own-ship position) can decrease taxi time by 10-15% (larger as the visibility decreases) while reducing the likelihood of navigation errors during taxi by 75% or more. In addition, subjective data received from pilots suggests that a CDTI does in fact increase situational awareness by increasing their confidence in surface traffic positions particularly in low visibility and during night operations.

As stated in the CDTI provisional policy, “IFATCA has no fundamental objection to the use of CDTI in areas where it is demonstrated to maintain and improve system safety”. Anyway, it should be noted that, according to ICAO operational requirements, when visibility conditions permit a safe and expeditious traffic flow, the A-SMGCS functions should primarily be based on standardised visual procedures. In case of specified LVO the use of some specified additional equipment or systems like CDTI can be considered according to well defined procedures. In this specific situation, ICAO has to define the specific type of separation standards, limitations and rules to apply (e.g. a new “CDTI separation”?).

The issue of ATC clearances and instructions to flight crews are based on the knowledge and awareness of the position and movement of aircraft and vehicles within the manoeuvring area. Controllers have to ensure that any authorised movement within this area can be safely accommodated.

Considering the apron and aircraft parking areas with all the movements of ground and ramp vehicles, it is not generally assumed that ATCOs are, effectively, responsible for the safe separations of aircraft and vehicles.

With increased needs to provide, in all weather operations, a safe guidance and control service for aircraft and controlled vehicles moving on the airport, as well as ensuring and monitoring the separation between them, the role of controllers will need to be supported by suitable equipment and procedures. Such system should provide the controller with the same coherent information displayed on the CDTI (i.e. cleared routing, obstacles, ground reference points, aircraft/vehicles positions etc.). In fact, the controller could provide an ATC guidance instruction referred to a specific ground reference point (e.g. “after windsock turn left..”). If the CDTI display does not show the same reference point, then the instruction will be meaning less for the crew. The same is true in reverse for the controller. In this context, suitable standards for airports databases and data-link formats should be defined.

ICAO currently writes standards for ground based systems, and only covers airborne systems which interface with ground systems. ICAO is firmly set against setting standards for airborne displays. This means that the CDTI in Boeing and Airbus aircraft could be different. From ATCO’s point of view this assumption could be a potential problem in terms of information coherency.

Where a route to follow or a traffic information is displayed to the pilot, ATCO should have it on his display as well. If not, whose is the responsibility that the pilot is following the correct route or the correct aircraft?

Some investigations are still required in consultation with IFALPA to come to an agreement on this subject and decide which areas require ICAO SARPS.


The goals for the next future ATC systems must remain to maintain and improve safety standards, increase system capacity and fully utilise capacity resources. The latter will include better accommodation of avionics capabilities.

The quality of information available to the system is a primary factor in determining the overall quality of the service. The future system will select the best sources of information and will utilise these data also to augment ground control systems capabilities.

A hypothetical integration between airborne and ground systems could lead to an increased level of Safety. This is especially valid when the roles played by Airborne system will be considered in a global co-ordinated approach and not as a separate domain.

It is anyway to be noted that, for the time being, no mature operational requirements have been issued on the possible integration between airborne and ground systems. Therefore, there is the need to continue in monitoring the evolution of possible “interoperability” issues between airborne and ground control systems.

The evolving use of airborne equipment derived data within the ground system could have the potential for providing benefits in safety, system capacity and efficiency. The evolutionary introduction of CDTI should not change the way in which controllers accomplish ATC tasks.

The airborne enabling technology is identified but the operational applications must be carefully managed. So, work on assessing specific uses of CDTI must continue and much more is needed before CDTI applications can be introduced.

Each application will require a clear statement regarding controllers and flight crew responsibilities allocation before implementation. However, some potential constraints, benefits and disadvantages can be identified since now.

There are already some limitation for the use of CDTI. In fact, in some cases the display could get extremely cluttered with each aircraft and vehicles displayed.

During some tests it was also noted that pilots had a tendency to fixate on the CDTI. This attitude could cause safety problems in a complex operational environment, where pilots need to maintain situation awareness through an effective scan out of the window. In addition some tests showed that current CDTI data were not really adequate for use in some applications. For example if a preceding aircraft is reducing speed it might be difficult to detect it until the distance from the following aircraft would be so reduced that safety is affected.

A global situational awareness comes from a comprehensive knowledge of aircraft and vehicles short, medium and long term’s intent as well as visual observations of current course and speed. In this sense, CDTI could be seen as a system to help flight crew to see and maintain useful knowledge of the relationships among traffic. CDTI derived data could also help ATC in an easily and safely integrated airport operations. Anyway, non-coherent or incomplete situation understanding for both pilots and controllers could lead to frequency congestion due to increased pilot’s traffic information request.

ATC operations in a mixed traffic environment will require specific assessment and procedures definition (i.e.: handling CDTI equipped and non-equipped traffic or co-operating and non-cooperating traffic).

IFATCA policy on this type of CDTI applications is required. So, the work study item should be confirmed for the next study cycle. Liaisons at appropriate IFATCA level should be activated to possibly determine “responsibility issues” deriving from integration between CDTI and ground control Systems.

At this stage, only some statements are possible:

  • CDTI application will require a clear statement regarding responsibilities allocation between the controller and the flight crew. Specific rules and procedures must be defined for safe CDTI-based operations;
  • CDTI operations must be proven safe and capable of supporting LVO;
  • Impact studies on ground ATC operations must be carried out, especially in a mixed traffic environment, through high fidelity simulations and field tests involving direct operational expertise;
  • CDTI requirements have to be carefully evaluated for the use in complex airport environment;
  • Impact studies on controller workload and RTF congestion have to be carried out;
  • Implementation of CDTI-based procedures must be preceded by appropriate verification and validation phase, followed by a reasonable period of stability to allow system bugs to be resolved;
  • In order to achieve controller acceptability of CDTI applications, it is important to involve controllers in the definition and implementation phase and to provide proper introduction and training;
  • No fundamental objection to the use of CDTI where it will be demonstrated to maintain or improve system safety and capacity;
  • Using CDTI for ground operations, it is important that vigilance outside the cockpit be not relaxed on board, for the purpose of detecting potential collisions;
  • It is necessary that global standards and responsibilities are defined in order to harmonise safety standards in CDTI applications.

Last Update: September 28, 2020  

December 21, 2019   868   Jean-Francois Lepage    1999    

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