Policy Review AAS 1.8 – 4D Trajectory Concepts / Management

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Policy Review AAS 1.8 – 4D Trajectory Concepts / Management

56TH ANNUAL CONFERENCE, Toronto, Canada, 15-19 May 2017

WP No. 91

Policy Review AAS 1.8 – 4D Trajectory Concepts / Management

Presented by TOC


This paper reviews the status and validity of two provisional IFATCA policy statements on 4D Trajectory Concepts/Management. The subject was investigated by TOC in 2007 and directors in 2008 Arusha Conference ratified current policy statements and status as “provisional”. It was foreseen that new technical and operational development would require periodic review of the subject and relevant IFATCA policies. Such review is presented in this paper. One policy statement is proposed for deletion. The wording of another provisional policy statement is proposed to be updated.


1.1 Concepts of 4D Trajectory Management have become the backbone for the development of future of Air Traffic Management. The idea of sharing four-dimension (4D) data of a flight and managing it in collaborative way is being studied and trialled by number of local projects and regional programs.

1.2 ICAO is drafting relevant Concept Document for Trajectory Based Operations (TBO) along the framework of Global ATM Operational Concept and Air Navigation System Block Upgrades (ASBU). 4D trajectories are an integral part of TBO.

1.3 IFATCA has been involved in following and participating several ways in the development of such concepts. IFATCA Conference in 2008 was presented with an investigation of 4D Trajectory Concepts. Provisional policies were accepted, which are under review by TOC with this working paper.


2.1 TOC investigation of 4D Trajectory Concepts for 2008 Conference resulted in working paper of 13 pages (no. 86). Information was gathered from several programs and trials involving 4D trajectory management at the time. Based on this information, TOC concluded:

3.1 4D trajectory management is already in limited operational use.

3.2 4D Trajectory is a key concept for ICAO, USA’s NGATS as well as Europe’s SESAR. Additionally, 4D Trajectories are being included in other country’s future ATM designs. Although there are different technologies and 4D ATM tools in development, for the most part the concept and proposed application of 4D trajectories is the same.

3.3 Reliable datalink is required in order to implement ATM Trajectory Management.

3.4 It is possible to implement 4D Trajectory Management in current airspace. However, in order to realise all the potential gains of a 4D ATM environment, airspace will have to be comprehensively redesigned.

3.5 TOC is of the opinion that a high equipage rate is crucial for a successful system wide the.

3.6 One of the issues to be resolved is the FMS must regard ATC requirements as hard requirements.


2.1.1 All of these conclusions are considered generally valid as of today by TOC. The working paper with such a foresight still provides comprehensive and valuable information on 4D trajectory management. Working Paper can be accessed from the IFATCA Office (office@ifatca.org) or from the new IFATCA website (TBN).

2.2 Directors in the 2008 Conference ratified two policy statements as proposed by the working paper. However, it was expected that review in the face of new development would be required before the year 2020. This is why these policies were included in the manual as “provisional” policies.

2.3 First the provisional policy statement thrives to ensure that aircraft flight management system (FMS) adheres to ATC requirements all the time. It had been identified in some instances certain FMS could suddenly be incompliant, for example speed constraints being disregarded.

IFATCA Technical and Professional Manual, 2016 issue, page 3 2 1 12:

The flight management system shall accept ATC requirements as compulsory requirements.


2.3.1 For the 2011 Conference, TOC made a broader study of Aircraft Flight Management Systems and their impact to ATM. The same issue with ATC requirements was identified, and eventually the exact same wording as in 4D policy was included in the Manual under title: AAS 1.12 AIRCRAFT FLIGHT MANAGEMENT SYSTEMS (page 3 2 1 16). However, now it was ratified as a “full” policy. As a result, there is a duplication of the same policy text in the manual with different status.

2.4 Another provisional policy from the 2008 Conference urges for airspace to be re-designed where 4D Trajectory Concept is Introduced.

IFATCA Technical and Professional Manual, 2016 issue, page 3 2 1 12:

Airspace must be designed to support 4D trajectory management.


2.4.1 In the Committee B discussions of the conference, it was already questioned that the wording in the policy would be requiring re-design even in airspace where 4D trajectory management is not implemented. Which apparently, was not the intention of the paper.

2.5 The Technical and Professional Manual also includes introductory text of the topic before the actual policy statements. Also, this can be considered valid and appropriate description of the 4D trajectory concept.

IFATCA Technical and Professional Manual, 2016 issue, page 3 2 1 12:

The combination of a standard three-dimensional route consisting of lateral, longitudinal and vertical guidance combined with time constraints is called a 4D-trajectory. 4D- trajectory management is the ability to manage an aircraft’s trajectory through each phase of flight ensuring that Air Traffic Management (ATM) resources are safely and efficiently used. A 4D contract is an agreement to follow a given 4D trajectory to reduce ambiguity of the aircraft position in time and space and so maximize available ATM resources for all users. Using computers and digital communication they can exchange several trajectories until both parties are satisfied. This process is called trajectory negotiation. Once the negotiation is completed, the pilot is responsible to comply with the 4D trajectory “contract”. Amendments to the contract are possible on request of the pilot or controller for any part of the flight. Automated tools provide pilot and controller with a visualization of an aircraft’s 4D-trajectory and allow these users to obtain more trajectories and are automatically communicated and negotiated between the ground systems and the aircraft involved via digital methods (datalink).


2.6 Regarding 4D trajectory management or Trajectory Based Operations in general, a few other IFATCA policies are relevant.

2.7 As referred to in the study from 2008, IFATCA ATS 3.13 MIXED MODE OPERATIONS1 policy applies to any implementation of 4D trajectory concept. Equipage and performance variations of aircraft FMS´s would be the most prominent reason for having to operate in mixed mode ATM environment. However, difference in Air Navigation Service Providers’ system capabilities have potential to add more “mixture” into controllers’ work, such as coordination procedures.

2.8 Most recent IFATCA policy, which is related to the 4D trajectory management is from the 2012 conference. Then, TOC studied the Controlled Time of Arrival (CTA) Concept, which is seen as a first step towards full 4D trajectory based operations. A list of requirements for CTA was added to the Technical and Professional Manual as a policy.

IFATCA Technical and Professional Manual, 2016 issue, page 3 2 3 36:


IFATCA supports the Controlled Time of Arrival concept provided;

  • Arrival Manager (AMAN) is available to define reliable CTA times.
  • RTA equipage level of aircraft is sufficient to support CTA operations.
  • Procedures and controller tools are available to integrate RTA equipped and nonequipped aircraft in the same traffic stream.
  • Tactical ATC interventions are always possible.
  • Accurate wind and temperature data is available.
  • Means to communicate the CTA contract with aircraft are available (preferably data link).


2.9 The Concept Document for Trajectory Based Operations is drafted by the ICAO ATMRPP (Air Traffic Management Requirements and Performance Panel). IFATCA is represented in this panel.

TBO draft definition by ICAO ATMRPP:

Trajectory Based Operations: A concept enabling globally consistent performance-based 4D trajectory management by sharing and managing trajectory information. TBO will enhance planning and execution of efficient flights, reducing potential conflicts and resolving upcoming network and system demand/capacity imbalances early. It covers ATM processes starting at the point an individual flight is being planned through flight execution to post flight activities.



3.1 IFATCA has two provisional policy statements regarding 4D Trajectory Concepts/Management as of 2008. Working Paper and the Introduction of these policies still provides valid information on the topic.

3.2 Duplication of the same policy text of Aircraft Flight Management Systems exists in the Technical and Professional Manual. Under the 4D Trajectory Concepts/Management title the policy is in provisional status, whilst under FMS title it is full policy.

3.3 TOC considers that, only where 4D trajectory management is implemented, airspace needs to be designed accordingly.

3.4 TOC also considers it apparent that the concept of 4D trajectory management is going to evolve significantly, especially with the development of Trajectory Based Operations. Thus, it is likely that the policy will need to be reviewed and further developed in a few years’ timeframe.


It is recommended that:

4.1 Provisional Policy in IFATCA Technical and Professional Manual 2016, AAS 1.8, page 3 2 1 12:

The flight management system shall accept ATC requirements as compulsory requirements.

is deleted.

4.2 Provisional Policy in IFATCA Technical and Professional Manual 2016, AAS 1.8, page 3 2 1 12:

Airspace must be designed to support 4D trajectory management.

Is amended to read:

Implementation of 4D trajectory management requires appropriately designed airspace.

Last Update: October 1, 2020  

December 22, 2019   832   Jean-Francois Lepage    2017    

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