Air/ground trajectory synchronisation via lateral and vertical complex CPDLC clearances

At EUROCONTROL, we are working to define and validate enhanced air and ground (A/G) operational procedures for trajectory-based operations (TBO) using controller-pilot datalink communications (CPDLC) clearances.

Such procedures can be used to:

  • perform immediate changes (for both lateral and vertical dimensions), or
  • anticipate and propose changes in advance, supported by datalink standards (ATN B1 and B2) and increased automation and use of ADS-C EPP information.

EUROCONTROL is leading the initiative, supported by 56 partners from across the industry, including air navigation service provides (ANSPs), airspace users (AUs) and industry representatives, to define and validate the operational and technical requirements supporting the improvement of the complex clearances to ensure the synchronisation of air and ground trajectories.


By anticipating changes and using complex CPDLC clearances, the new procedures allow a better alignment of the airborne and ground trajectories. This helps to:

  • increase predictability;
  • improve certainty in flight deck situational awareness (schedule airline or business jets);
  • provide useful trajectory data from the aircraft;
  • better manage both flight crew and air traffic controller (ATCO) planning and resources;
  • increase capacity and flight efficiency.

Complex clearances

Complex clearances are communications of reference business trajectory (RBT) revisions, supplementing the basic information, from the air traffic service unit (ATSU) to the aircraft using datalink. Their transmission is triggered by issues detected by the 2D or 3D consistency checks to ensure the synchronisation of the air and ground trajectories. Complex clearances sent in advance can be initiated by a downstream sector or a third party (e.g. extended planner) in the same, or a different centre.

Background and plan

Our work builds on research performed under SESAR 2020’s Wave 1. We plan to develop new complex clearances to improve the A/G trajectory synchronisation (mainly vertical clearances).

We will place a particular focus on automation and will assess the possibilities, benefits and implications inherent to increasing the level of automation in ATC tasks. The assessment will consider the impact of:

  • automation of the clearances uplinking;
  • increasing the use of the auto-load to flight management systems (FMS) of uplinked clearances and managed/automatic mode by the flight crew.


As part of this project we will perform two real-time simulations looking at enhanced operational procedures (ATC and airborne) for 3D trajectory changes.

We have also proposed a series of large-scale demonstrations to validate lateral route modification in advance and other complex CPDLC clearances as well as increased automation using relevant extended projection profile (EPP) information (clearance generation, transmission without ATCO intervention) and including MSP / EAP.

Interested in our validation solutions

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Our work is part of a SESAR 2020 Wave 2 project solution 56, performed in partnership with AIRBUS, PANSA, COOPANS, Thales Avionics and airspace users.