The importance of TOBT in the A-CDM Light (Advanced ATC Tower) certification

2 February 2024

The A-CDM & A-CDM Light concept

Airports are very busy places where the various stakeholders have key roles and a common goal : safely and efficiently manage the flow of departing and arriving flights.

With an anticipation of 3 hours, the airport collaborative decision-making (A-CDM) process allows all stakeholders to benefit as soon as possible from the same shared information in order to make informed decisions. Milestones and relevant flight details are updated and shared in order to have precise block departure times (OBT) and take-off times (TOT) for better situational awareness. This information sharing leads to better management of traffic flows at the level of the European Eurocontrol NM network.

This objective is reflected in the light version of the A-CDM (A-CDM Light or Advanced ATC Tower) by a need for communication between all the actors of the airport, the partners but also the NM network, information on the departure flights, includes:

  • A reliable take-off estimate (TTOT)
  • An updated departure circuit information (SID)


The importance of the TOBT in the A-CDM Light certification


The target time for the block start and the reliability of the take-off time


The TOBT (Target Off-Block Time) is the target time defined as the block departure time by the airline or the airport assistant. At this time, the following milestones must be achieved:

  • the doors of the plane are closed;
  • the boarding bridge is disconnected from the device;
  • pushback vehicle is available;
  • the aircraft is ready to start / push back upon authorization by the air traffic controller.


The TOBT and its subsequent updates is key to improving predictability during the aircraft rotation process.

In particular, it contributes to better allocation of parking lot resources thanks to knowledge of parking lot occupancy time and the accuracy of aircraft parking allocation.

It also contributes to better management of the workload of air traffic controllers who can anticipate the number of flights using the platform simultaneously.

Elle contribue aussi à une meilleure gestion de la charge de travail des contrôleurs aériens qui peuvent anticiper le nombre de vols utilisant la plateforme simultanément.

Finally, thanks to variable taxi times (VTT), a better forecast of take-off times (TTOT) can be communicated to the network manager’s operations center.



In order to provide reliable take-off time to partners as well as to the network, the objective block departure time (TOBT) is essential, in association with the estimated taxi time.


TOBT cycle life


The TOBT is declared manually by the airline company or ground handling team in charge of the flight. It is observed that the TOBT is updated very late (i.e. shortly before the current TOBT). This is due to various reasons among which:

  • Airport ground assistants are focused on preparing the aircraft to perform the pushback on time, rather than communicating reliable time to other participants.
  • The parking fees are proportional to the time the stand is occupied, the job of the handlers is therefore to try to minimize this time (it should be noted that in some cases the airport assistants receive penalties when the delay can be attributed to them).
  • Ground assistants do not want to lose their place in the departure sequence, which would result in a longer delay (when TOBT changes, certain rules are applied by air traffic control, which may result in the flight being removed from the departure sequence and its reprogramming in this sequence later).

Certain events are beyond the control of the ground assistants, and they have no control over them (boarding longer than usual, no-show of passengers, etc.).

Therefore, TOBTs are only updated when the issue is confirmed and no other option is possible, meaning that updates occur very late in the flight lifecycle.

This is a sore point in the A-CDM information sharing objective.

To overcome these operational constraints, it then becomes crucial to be able to predict the TOBTs that will be issued in order to anticipate future updates of the TOBT and thus allow all stakeholders to react more effectively to these schedule changes. . We will call the block start time prediction the POBT (Predicted Off-Block Time) in the rest of this article.


Simplified monitoring of the target time for block departure thanks to AirportKeeper


AirportKeeper is based on an approach using the different milestones of the aircraft operating their rotations on the airports using the solution in order to calculate a POBT for each departing flight.

This POBT is then compared to the target starting time of the block communicated by the station assistants (TOBT) in order to allow anomaly detection and an associated alert lifting named TOBT_UPDATE in AirportKeeper.

Thanks to this monitoring of the communicated objective block departure times, AirportKeeper makes it possible to alert on non-updated TOBTs and therefore to facilitate and make their updates generally more reliable.

This support for operations in the tactical phase thus enables the obtaining of A-CDM Light (Advanced ATC Tower) certification in the airports where it is deployed and where the reliability and stability of the TOBT transmitted to the network is essential.