Review Issues in the Application of Cockpit Display of Traffic Information (CDTI) in Advanced Surface Movement Guidance System (A-SMGCS) Operations

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Review Issues in the Application of Cockpit Display of Traffic Information (CDTI) in Advanced Surface Movement Guidance System (A-SMGCS) Operations

40TH ANNUAL CONFERENCE, Geneva, Switzerland, 19-23 March 2001

WP No. 86

Review Issues in the Application of Cockpit Display of Traffic Information (CDTI) in Advanced Surface Movement Guidance System (A-SMGCS) Operations


At the 39th IFATCA conference in Morocco, SC1 accepted the work item concerning the review of CDTI applications in the airport environment. In this framework, SC1 was asked to develop a policy on the use of CDTI with Advanced Surface Movement Guidance and Control Systems (A-SMGCS).

The term Cockpit Display of Traffic Information (CDTI) refers to a generic avionics display in an aircraft cockpit that is capable of displaying surveillance information about the surrounding traffic to the flight crew. The information presented includes the relative position of other aircraft/vehicles in the vicinity with respect to own aircraft and may also include display of ground reference points, navigation and/or routings information to increase the pilot’s situational awareness and understanding of the ATC instructions.

At present, no standards are available on CDTI and his applications and there is no uniqueness in the use of relevant terminology.

The purpose of this paper is to provide further information and requirements in order to review the relevant issues and to define an IFATCA policy for potential applications of CDTI with A- SMGCS.


The previous paper on the subject, presented at Marrakech Conference, proposed the following conclusions:

  • IFATCA supports the use of CDTI with A-SMGCS where it is proved to enhance safety while improving airport system efficiency and capacity with an acceptable level of workload for both controllers and pilots;
  • Where separation assurance is concerned, it shall be clearly indicated that this function remains an ATC primary task, until a definitive assessment of CDTI used with A-SMGCS relevant applications and performances will become available.

In the A-SMGCS, CDTI could increase situational awareness by increasing pilot’s confidence in surface traffic positions in low visibility and during night operations. Flight crews could be provided with an enhanced guidance function on the airport and improved traffic situational awareness. Furthermore, a suitable CDTI could enable, during low visibility operations (LVO), higher taxi speeds and traffic flow. CDTI could also play a role in detecting potential conflicts and reducing the likelihood of navigation errors, runway incursions and airport accidents.

The operational use of CDTI in the A-SMGCS will interact with its technical aspects, with consequences for safety and criticality. As for any new equipment or procedures, the introduction of CDTI applications will require assurance they meet the safety objectives, which have been allocated. A-SMGCS operations should be based on the use of CDTI only when the procedures agreed for its use will provide the level of safety normally required for that operations. Therefore, the safety of each individual CDTI application must be assessed before its operational use.

At present, the development, certification, and regulation of aircraft systems are conducted separately from those of ground systems. However, the growing air-to-air and air-to-ground interactions transcend any single institution and need a co-ordinated process. It is desirable that safety assessment of CDTI and its applications are considered as a consistent whole with the appropriate ground A-SMGCS components.

Where CDTI should be used for each of the A-SMGCS functions (Guidance, Surveillance, Control and Routing), the airborne systems must comply with the same equipment standards as the ground equipment in terms of latency, integrity, reliability, accuracy, update rate and continuity of service.

ICAO currently writes standards for ground-based systems, and only covers airborne systems, which interface with ground systems. ICAO is set against the definition of standards for airborne displays. The problem is that there are currently no standards for the format of data displayed on the CDTI. 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 consistency for the operations and ICAO standards are needed for both CDTI and ATC display. Investigations are required in consultation with IFALPA to come to an agreement on this subject and decide which areas require ICAO SARPS.

A-SMGCS should act, in all weather conditions, providing an integrated multi-sensor surveillance and communication system for continuous automatic determination of the traffic situation at the airport. In mixed traffic environment (equipped and not equipped and/or not co-operating), depending on the specific system architecture, the CDTI could not receive surveillance data for all aircraft/vehicles. Crews must be aware of the fact that non-equipped or non-co-operating aircraft/vehicles will not be presented on the CDTI. In these circumstances, the CDTI could provide flight crew whit a false and unsafe sense of security since it would not necessarily display all the relevant traffic.

During the transition phase with a mixed population of non-equipped or non-cooperating traffic interacting with suitably equipped aircraft, it will be necessary to consider which applications are feasible to implement. It could be possible to provide position information to equipped aircraft about non-equipped or non-co-operating aircraft/vehicles through implementation of functions such as ground TIS-B.

If the CDTI utilises surveillance data from different sources, the position accuracy of the displayed data might not be mutually consistent. Therefore, flight crew interpretation of the data might not be appropriate. This situation could be avoided, potentially, by requiring a minimum level of data accuracy for any aircraft that is displayed or by using different target symbols.

The use of TIS-B to increase the integrity of the surveillance data could exacerbate this problem. In fact, the use of data from more than one source creates the risk that a single aircraft/vehicle could be represented by more than one target symbol. Again, this could present problems for the correct interpretation of the CDTI data.

At this stage, it is still an open question whether surveillance data (provided by ADS-B, TIS-B etc.) will have sufficient integrity, reliability, accuracy and continuity of service to support all CDTI applications. Data fusion from different sources might be used to increase the integrity of the surveillance data, but in this case it will need to be demonstrated that common failure modes are not introduced with ground-based systems if TIS-B is used. In particular, as ADS-B could be central to both airborne and ground surveillance, a failure in ADS-B might lead to an increased risk of safety reduction in the A-SMGCS through simultaneous loss of both airborne and ground surveillance systems.

The airborne system must show the same information as the ground system. This problem needs to be pursued further to find the best way of ensuring that all the information will be available to both the controller and the pilots. Non-coherent or incomplete situation understanding for both pilots and controllers has the potential to increase the workload of ATCOs and could lead to frequency congestion due to increased pilots’ traffic information request. Nevertheless, ATC workload could also be reduced since they may not be required to issue repeated traffic advisories.

During LVO the controller should be provided with means to identify CDTI-equipped aircraft and with tools to identify potential conflict or runway incursions. In particular, ATC and CDTI alerting systems for conflict detection and runway incursion might be required to support and maintain the safety in a complex A-SMGCS environment during LVO. Considering the specific system architecture, it is still an open issue if these alerting systems should be different on the ground based ATC system and in the airborne system to avoid common failure mode or not.

The relevant CDTI surveillance data requirements should be application dependent. For some applications, the surveillance data displayed on the CDTI will need to be with very low latency. A clear set of minimum requirements for communications, navigation, and surveillance (CNS) systems that will support the potential CDTI applications in A-SMGCS has to be still defined.

CDTI applications will require implementation of new procedures and new rules to be applied both by pilots and controllers. It will be necessary to ensure that such new procedures are feasible and safe, taking into consideration the workloads of both the controllers and pilots considering the A-SMGCS environment (i.e. traffic density, visibility conditions and airport complexity) in which the application would be used.

Specific flight crew training must be provided to ensure correct interpretation and use of CDTI in the A-SMGCS. Also relevant ATC training requirements must be addressed. Training aspects should be focused on new relations and responsibilities between flight crews and controllers.


Current procedures, visual aids, radio communications and human performance enable safe airport surface operations at near peak flow rates in conditions of good visibility. According to ICAO operational requirements and taking into account the results of different field experiments (e.g. US-FAA/ASTA, LVLASO etc.), when visibility condition permit a safe and expeditious traffic flow, the A-SMGCS functions should be primarily based on presently standardised procedures. Only in case of specified LVO (Low Visibility Operations) the use of CDTI can be considered according to well-defined procedures. In that specific situation, the relevant type of separation standards, responsibility allocation, limitations and rules to apply have to be defined.

It is however arguable that many of the applications being investigated and developed, as part of the evolution of the CDTI in A-SMGCS context and the evolving use of airborne equipment and their derived data within the ground system, could have the potential for providing benefits in terms of safety, capacity and efficiency during LVO. So, work on assessing specific uses of CDTI must continue and much more is needed before these applications can be introduced.

The evolutionary introduction of CDTI should not change the way in which controllers accomplish ATC tasks. ATC operations in a mixed traffic environment will require specific assessment and procedures definition (e.g.: handling CDTI equipped and non-equipped traffic or co-operating and non-co-operating traffic, etc.). An essential requirement will be the provision of position information to the cockpit of equipped aircraft about non-equipped or non-co-operating aircraft/vehicles through implementation of functions such as ground TIS-B.

The development of CDTI equipment and applications in A-SMGCS will follow the work being done by different groups. That development will need to address the many human factors and technical concerns that have been identified in the research so far. For this reason it is essential that IFATCA continues to closely monitor developments within relevant groups.

To do so effectively IFATCA must have a clear unambiguous policy on the relevant issues involved in order to provide guidance to representatives in the various forums. This policy should take account of developing technology that will, theoretically, extend the feasibility of CDTI applications beyond the current limits.

The use of CDTI in A-SMGCS operations will need to address the many human factors and technical concerns that have been identified in the research so far.

It is recommended that:

FATCA supports development and implementation of CDTI in A-SMGCS applications to enhance safety and improve the efficiency of airport ground operations, provided that there are no adverse impact on controller and pilot workload.

Where any CDTI assurance function will be implemented, a clear and unambiguous statement of the responsibilities between pilots and controllers is required.

International standards should be established for certification and approval of complementary CDTI systems.

IFATCA considers the following to be the minimum attributes of CDTI used in A-SMGCS:

  • Positive unambiguous identification of all relevant aircraft/vehicles should be provided to the standards required for ATC systems.
  • Sufficient information as to ground reference points, guidance and/or routings of relevant aircraft/vehicles should be provided to increase pilot’s situational awareness and understanding of ATC instructions.
  • All aircraft/vehicle should be displayed.


Proposed Operational Requirements for A-SMGCS, Draft 9, European Air Navigation Planning Group, Aerodrome Operations Group, Paris, May 1995.

Minimum Aviation System Performance Standards for Automatic Dependent Surveillance Broadcast (ADS-B), RTCA (1998), Document No. RTCA/DO-242.

Minimum Operational Performance Standards for Cockpit Display of Traffic Information, Draft 25a, RTCA (1999), Document No. RTCA/DO-???

Achieving early CDTI Capability With ADS-B, A. D. Zeitlin & Others, MITRE/CAASD (1998).

Demonstration of Integrated Airport Surface Automation Concepts, D. R. Jones, S. D. Young, AIAA/IEEE 14th Digital Avionics Systems Conference (1995).

Positive Identification of Aircraft on Surface Movement Areas – Results of FAA Trials, Rick Castaldo, Federal Aviation Administration (1996).

Atlanta Hartsfield International Airport-Results of FAA Trials to Accurately Locate/Identify Aircraft on the Airport Movement Area, Rick Castaldo, PM for ASTA, Federal Aviation Administration (1998).

Flight Demonstration of Integrated Airport Surface Technologies for Increased Capacity and Safety, Denise R. Jones, Steven D. Young et Others, NASA/TM-1998-206930.

Comparison of A-SMGCS requirements with observed performance of an integrated Airport CNS system, S.D.Young, NASA-Langley Research Center, 1999.

Last Update: September 29, 2020  

March 12, 2020   143   Jean-Francois Lepage    2001    

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