Improving TOBT predictability using actual ready time

Many major European airports have been improving their operational efficiency by implementing Airport CDM information sharing. Some, however, have opted out of a few of the recommended milestones in order to shortcut the implementation process. Not implementing actual event milestones means the airport misses out on benefits by settling for non-optimal predictability.

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Milestones for continued improvement

The EUROCONTROL Airport CDM Manual (pdf) presents a Milestone Approach with 16 Recommended and Highly Recommended Milestones for the turn-around process to further improve effectiveness after implementing A-CDM information sharing. This approach aims to achieve common situational awareness by tracking the progress of a flight from initial planning, through inbound to take off.

The choice to skip recommended milestones can come from a temptation to implement A-CDM faster, or because the potential benefits are not fully understood. However, when Target Off-Block Time (TOBT) is validated, the benefits of enhanced traffic demand predictability for the local airport and the entire network are difficult to understate.

Increasing A-CDM effectiveness

Recommended milestones such as Actual Commence (and End) of Ground Handling (ACGT, Milestone 8), Boarding Starts (Milestone 11) and Aircraft Ready (ARDT, Milestone 12) are intended to validate and improve TOBT predictions. Not implementing these milestones allows inaccurate predictions to stand with no performance feedback. As a consequence, too many flights are not ready at their predicted TOBT and occupy stands longer than expected. Virtual runway space that could be used for flights that are ready experience delayed TSAT instead. Moreover, sub-optimal take-off predictions lead to unreliable sector demand calculations and hence an unnecessarily high amount of ATFM regulation through CTOTs.

Particularly the Actual Ready for Departure Time (ARDT, Milestone 12), is crucial for effective performance feedback. The ARDT is a direct validation of TOBT, making it the most relevant parameter for assessing the accuracy of the TOBT.

Each flight progress event leading to the ARDT requires an independent timestamp source for determining the exact moment of the instance. Sources can be data from airport, ground handling, or airline systems that indicate actual ready times of the aircraft, pushback truck and flight crew. (To avoid human error in the performance monitoring, timestamp sources should be automated.)

Actual milestones such as ARDT can be actively used as enablers by pre-departure sequencer business rules, improving or swapping TSAT for flights verifiably advancing their flight progress. Anticipating on actual flight progress increases flexibility for ready aircraft and contributes to using available runway slots missed by others.

Enhancing predictability

To achieve enhanced predictability, the main airport partners need to steer on predictability indicators rather than time performance. Steering on predictability not only reduces the stress of working towards a deadline (and associated risks), but it also contributes to a more optimum use of resources and eventually reducing capacity buffers.

The solution to improving future airport operations is for all A-CDM partners to collaboratively manage operations based on performance efficiency. In our experience, cross-functional A-CDM project teams working together with operational experts from ground handling, air traffic control, aircraft operators and the airport are the best way to implement actual milestones and analyse performance to continuously improve predictability.

About To70. 
To70 is one of the world’s leading aviation consultancies, founded in the Netherlands with offices in Europe, Australia, Asia, and Latin America. To70 believes that society’s growing demand for transport and mobility can be met in a safe, efficient, environmentally friendly and economically viable manner. To achieve this, policy and business decisions have to be based on objective information. With our diverse team of specialists and generalists to70 provides pragmatic solutions and expert advice, based on high-quality data-driven analyses. For more information, please refer to

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