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Technical article · Reading time ~11 min
By the ITAérea faculty
A-CDM (Airport Collaborative Decision Making) is a working method in which the airport operator, the airlines, the ground handling agents and air traffic control share the same real-time information on every flight and take decisions together. Its purpose is to reduce delays, make the operation predictable and make better use of resources such as stands and the runway.
Several companies touch the same aircraft during each turnaround, each working to its own clock; A-CDM gets them to agree on one time. So, what is A-CDM in practice? Below you will find its 16 milestones, who takes part and where it already runs, as part of airport management.
The essentials in 30 seconds
- What it is: a process, not a piece of software: everyone shares the data on each flight and follows common rules.
- Who takes part: the airport operator, the airlines, ground handling, air traffic control and Eurocontrol’s Network Manager.
- The key time: the TOBT (Target Off-Block Time), set by the airline or its ground handler.
- Where it runs: as of 25 September 2026, 34 European airports according to Eurocontrol, five of them operated by Aena, and El Dorado (Bogotá) according to OPAIN and SITA.
What is A-CDM (Airport Collaborative Decision Making)
It is a concept for improving air traffic flow and capacity management at airports: fewer delays, more predictability and better use of resources, according to Eurocontrol’s concept page and its Implementation Manual v5.0, in force as of 25 September 2026.
Aena, the Spanish airport operator, attributes the concept in its press release of 19 December 2022 to Eurocontrol, ACI Europe (Airports Council International Europe, the European airports’ association), CANSO (Civil Air Navigation Services Organisation, the air navigation service providers) and IATA (International Air Transport Association, the airlines). It is not a software product but an agreement between partners built on a shared information platform.
What does CDM mean in aviation
Collaborative Decision Making: deciding on the basis of data shared between separate organisations, also in air traffic flow management (ATFM, Air Traffic Flow Management) at network level. A-CDM is its airport version. ICAO (International Civil Aviation Organization) covers collaborative decision making, including at airport level, in its Manual on Collaborative Air Traffic Flow Management (Doc 9971), and in the United States the FAA (Federal Aviation Administration) runs its own CDM programme with airlines and other stakeholders, centred on traffic flow management. More on what ICAO is.
What problem A-CDM solves in an aircraft turnaround
Fragmented information: each actor plans with its own time (flight plan, loading and boarding, tower, network). The result? Aircraft waiting at the holding point with engines running, stands reassigned at the last minute and a network that does not know when each flight will actually take off. Now, who sits at the table.
Who takes part in A-CDM: actors and responsibilities
Four parties: the airport operator, the airlines with their ground handling agents, air traffic control (ATC, Air Traffic Control) and Eurocontrol’s Network Manager, each responsible for one of the process times according to the v5.0 manual.
Airport operator
In Spain, that is Aena; elsewhere it may be a public authority, a concession company or an airport group, with the same role. It plans stands and gates using the target times it receives from the ATC sequencer, and it is the party that suffers most from late changes. This is the territory of the airport operations technician.
Airlines and ground handling agents
The airline holds overall responsibility for the TOBT and may delegate its updating to the ground handler; exceptionally, the flight crew manages it. Whoever watches boarding and loading progress has the accurate figure: ground handling sustains, or degrades, the precision of the whole system.
Air traffic control (ATC)
Clearance delivery monitors the TOBT and, through the pre-departure sequencer, assigns the TSAT (Target Start-Up Approval Time) and the TTOT (Target Take-Off Time). Apron control approves start-up and pushback.
Eurocontrol’s Network Manager
It manages the European network. It assigns the CTOT (Calculated Take-Off Time) to regulated flights and receives from the airport the DPI (Departure Planning Information) messages carrying each flight’s TTOT. Outside the Eurocontrol area, this role falls to the national or regional ATFM unit. Now, the order in which they act.
How A-CDM works: the 16 milestones of the process
It follows every flight through 16 milestones, from flight plan to take-off; at each one an actual time or an estimate is recorded, and everyone sees it at once.
The six elements of the A-CDM concept
According to the v5.0 manual: information sharing; the milestone approach; variable taxi time; pre-departure sequencing; adverse conditions management; and collaborative management of flight updates, through FUM (Flight Update Message) and DPI messages exchanged with the Network Manager.
Table of the 16 A-CDM milestones
Section 3.3.3 of Eurocontrol’s v5.0 manual (31 March 2017). EOBT (Estimated Off-Block Time): the estimated off-block time filed in the flight plan.
| Milestone | Name in the manual | What it marks | Time reference |
|---|---|---|---|
| 1 | ATC Flight Plan activation | The ATC flight plan is activated | 3 hours before EOBT |
| 2 | EOBT – 2 hr | Two hours to the estimated off-block time | 2 hours before EOBT |
| 3 | Take off from outstation | Departure from the origin airport | ATOT at the outstation |
| 4 | Local radar update | Local radar picks up the inbound flight | Airport-specific |
| 5 | Final approach | The aircraft is on final approach | Airport-specific |
| 6 | Landing | Landing | ALDT |
| 7 | In-block | The aircraft is on stand (on blocks) | AIBT |
| 8 | Ground handling starts | Ground handling begins | ACGT |
| 9 | TOBT update prior to TSAT | The TOBT is confirmed before the TSAT is issued | Airport-specific |
| 10 | TSAT issue | The TSAT is issued | 30 to 40 minutes before TOBT |
| 11 | Boarding starts | Boarding begins | Airport-specific |
| 12 | Aircraft ready | The aircraft is ready | ARDT |
| 13 | Start up request | Start-up is requested | ASRT |
| 14 | Start up approved | Start-up is approved | ASAT |
| 15 | Off-block | The aircraft leaves the stand (off blocks) | AOBT |
| 16 | Take off | Take-off | ATOT |
The initial “A” in the table’s acronyms (ALDT, AIBT and so on) stands for Actual: the time actually recorded.
The milestones, phase by phase
Four moments (a teaching grouping of our own, not the manual’s) with a worked example, not a real flight, with an EOBT of 14:00.
Flight planning (milestones 1 and 2)
At 11:00, three hours before EOBT, the flight plan is activated, checked against the airport slot, and the first DPI goes out to the network. At 12:00 (milestone 2) the ATFM slot is usually issued if a regulation applies.
The inbound flight (milestones 3 to 6)
On departure from the outstation (3) the estimated landing and in-block times are updated; local radar picks the flight up (4), it turns onto final approach (5) and lands (6), refining the stand and departure forecast at each step.
The turnaround on the apron (milestones 7 to 12)
The aircraft arrives on stand (7) and ground handling starts (8). This is where it matters: the handler confirms the TOBT (9) and ATC issues the TSAT 30 to 40 minutes beforehand (10); with a TOBT of 14:00, our flight knows it at around 13:20. Boarding (11) and aircraft ready (12).
Start-up, pushback and take-off (milestones 13 to 16)
The crew requests start-up (13), the tower approves it (14), the aircraft goes off-block (15) and takes off (16); the actual time goes back to the network by DPI and closes the loop. Everything hinges on three times: TOBT, TSAT and TTOT.
TOBT, TSAT and TTOT: the times that order every departure
The TOBT says when the aircraft will be ready; the TSAT, when it can expect start-up approval; the TTOT, when it will take off. Different actors set them.
What the TOBT is and who sets it
It is the time at which the aircraft operator or its ground handler estimates the aircraft will be ready: doors closed, boarding bridge removed, pushback tractor available and ready to start up or push back on receipt of clearance. The system does not assign it, and it degrades when updated late: the manual requires it to be corrected as soon as a delay is detected.
Difference between EOBT and TOBT
The EOBT is the flight plan forecast, filed hours in advance; the TOBT is the operational commitment of the day, updated with the real turnaround. In other words: what was planned against what is actually happening.
What the TSAT is
It is the time assigned by ATC, taking into account the TOBT, the CTOT if there is one and the traffic situation, at which the aircraft can expect start-up or pushback approval. The actual approval (ASAT) may come earlier.
TTOT and CTOT: from the airport to the European network
The TTOT is the TOBT or the TSAT plus the estimated taxi-out time (EXOT, Estimated Taxi-Out Time), and it travels to the network in the DPI messages. The CTOT is issued by the Network Manager when the flight is subject to an ATFM regulation; after start-up, ATC is responsible for meeting it.
| Time | What it is | Who sets it |
|---|---|---|
| EOBT | Estimated off-block time filed in the flight plan | Aircraft operator, in the flight plan |
| TOBT | Target time at which the aircraft will be ready to depart | Aircraft operator; may delegate it to its ground handler |
| TSAT | Target start-up approval time | ATC, through the pre-departure sequencer |
| TTOT | Target take-off time (TOBT/TSAT + taxi time) | ATC, through the sequencer; sent to the network in DPI messages |
| CTOT | Calculated take-off time under an ATFM regulation | Network Manager (Eurocontrol) |
Airport slot and CTOT are not the same thing
The airport slot is the arrival or departure window allocated in seasonal scheduling; the CTOT is the ATFM slot of the day, given by the Network Manager when a regulation applies. And now, where it is already running.
Which airports have A-CDM
As of 25 September 2026, 34 European airports have fully implemented A-CDM according to Eurocontrol’s list, five of them operated by Aena; in Latin America, El Dorado (Bogotá) is presented as the pioneer.
Spanish airports with A-CDM
According to Aena’s press release of 19 December 2022, it operates at Adolfo Suárez Madrid-Barajas, Josep Tarradellas Barcelona-El Prat, Palma de Mallorca, Málaga-Costa del Sol and Alicante-Elche Miguel Hernández. Alicante was the fifth, in December 2022, and the first single-runway airport in the network to join.
eCDM, Aena’s platform
eCDM is the portal through which Aena gives registered access to A-CDM to airlines, ground handlers, ATC and the operator itself.
Advanced ATC Tower: the step before A-CDM
The Advanced ATC Tower is the first rung: airport, tower and Eurocontrol share information in real time without the full process. Alicante was the first in Spain, in 2016, according to Aena’s 2022 release.
A-CDM in Europe according to Eurocontrol
Its concept page maintains the list of fully implemented airports: 34 as of 25 September 2026, the five Spanish ones included. Many texts repeat old, undated figures.
A-CDM in Latin America
El Dorado would be the first airport in Latin America with A-CDM, according to OPAIN and SITA, who lead the project (Airline92, 23 May 2025). The regional reference is ICAO’s A-CDM implementation guide for the CAR/SAM regions, produced by GREPECAS (the Caribbean and South American Regional Planning and Implementation Group). And now, what it delivers.
Benefits of A-CDM for airlines, airports and passengers
Three fronts: less taxiing with engines running, better punctuality and more predictable take-off times. The only figures with a primary source are Eurocontrol’s from 2016.
What Eurocontrol’s data say
Eurocontrol’s 2016 A-CDM impact assessment, based on data from 17 CDM airports, measured average taxi-out savings of 0.25 to 3 minutes per departure and punctuality gains against schedule of 0.5 to 2 minutes per flight. The same study found take-off predictability improved by up to 85% in adverse conditions, with the standard deviation of take-off time falling from 14 minutes to about 7 at sequencing and 5 at off-block.
Assuming EUR 2.5 million of implementation cost and EUR 150,000 a year in maintenance, the assessment estimated a return on investment within 18 months and a cost-benefit ratio of 7 over ten years, counting only the airlines’ tactical savings. In January 2016, 34% of departures in the ECAC area (European Civil Aviation Conference) already left from CDM airports, according to the study. These are 2016 figures, not today’s.
Benefits for each actor
| Actor | Main benefit | Source |
|---|---|---|
| Airlines | Less taxiing and less fuel; better compliance with the ATFM slot | Eurocontrol, 2016 |
| Ground handling agents | Data available earlier to plan staff and equipment | Aena, 2022; Eurocontrol, 2016 |
| Airport operator | Fewer late stand or gate changes; more departures in the peak hour | Eurocontrol, 2016 |
| ATC and the European network | More predictable take-off times and better-tuned regulations | Eurocontrol, 2016 |
| Passengers | Better punctuality, fewer missed connections and better information during disruptions | Aena, 2022 |
| Environment | Less time with engines running while taxiing and at the holding point (in qualitative terms) | Aena, 2022 |
They do not come with the platform but with the full process, which has an order.
How A-CDM is implemented at an airport
Element by element, in the order set by the v5.0 manual, from information sharing to the link with the European network; it is not an IT project but a change of procedures.
Order of implementation of the elements
Information sharing first; then the milestones, variable taxi time and pre-departure sequencing, before adverse conditions management. Finally, the airport connects to the Network Manager through DPI messages. At smaller airports, the Advanced ATC Tower is the light alternative.
Is there an A-CDM certification?
No. According to the v5.0 manual (2017), there is no international regulation and no A-CDM label: Eurocontrol only issues a certificate recognising implementation with a DPI connection to the network, and each airport validates its results with indicators. As for training, each partner trains its own staff; Eurocontrol offers courses and recommends joint sessions.
The challenges: data, culture and TOBT discipline
Three: data quality, because a platform fed with bad times is worse than none; the cultural shift of sharing information with someone who yesterday was only a supplier or a customer; and TOBT discipline, where that shift shows every day.
From A-CDM to Airport 4.0: AOP, APOC and integrated management
Airport 4.0 is built on shared data, and A-CDM is its first layer. On top of it sit the AOP (Airport Operations Plan), the APOC (Airport Operations Centre) and analytics.
What is the difference between A-CDM and AOP
A-CDM organises the process of each flight; the AOP is a single, common, collaboratively agreed plan covering aircraft and terminal and linked to the Network Operations Plan (NOP, Network Operations Plan), according to Eurocontrol (13 November 2018). Dublin Airport sums it up: A-CDM is the foundation of the AOP. The APOC is the physical centre where that plan is managed; not every airport needs one.
| Advanced ATC Tower | A-CDM | AOP | |
|---|---|---|---|
| What it is | Real-time information exchange between the airport, the tower and Eurocontrol | Collaborative process with six elements and 16 milestones per flight, connected to the network by DPI messages | Single, agreed operations plan linked to the network plan (NOP) |
| Scope | Departure data shared with the network, without the full process | The complete turnaround of every flight, from flight plan to take-off | Aircraft and terminal: the airport’s operation as a whole |
| Prerequisite | None specific: it is the first rung | Information sharing and milestones before the other elements | An implemented A-CDM to build on |
Shared data and AI in airport operations management
With reliable times shared by everyone, analytics and artificial intelligence at airports have something to work with: spotting TOBT deviations, anticipating which stand will come free or simulating a stormy afternoon. Without A-CDM, they feed on times nobody has validated.
Frequently asked questions about A-CDM
What happens if the TOBT is not met?
If the TOBT passes, plus the tolerance each airport sets, and the aircraft is not ready, the platform alerts the airline or the ground handler so that they update it. The new TOBT generates a new TSAT and may cost the flight its position in the departure sequence.
When is an airport considered a CDM airport?
According to the v5.0 manual, when it has implemented the six elements of the concept. Eurocontrol also includes it in its “fully implemented” list when it exchanges DPI messages with the Network Manager, that is, when its take-off times feed the management of the network.
Are A-CDM and ATFM the same thing?
No. ATFM manages traffic flow at network level, the domain of the Network Manager and the CTOT; A-CDM organises the process inside the airport. They connect through DPI messages, from the airport to the network, and FUM messages, from the network to the airport.
Who works with A-CDM day to day?
Airport operations technicians, ground handling and ramp coordinators, airline dispatchers and operations staff, and tower and apron controllers. At management level, the heads of operations who set the procedures: the profile a master’s degree in airport and aeronautical management is aimed at.
Conclusion: A-CDM, the shared foundation of the efficient airport
What is A-CDM, in one sentence: the decision that everyone who touches an aircraft on the ground works with the same information and answers for their part. Common data instead of parallel clocks; the TOBT as a commitment with an owner; and, on that foundation, the AOP, the APOC and Airport 4.0. The technology is bought in months; the culture of sharing data takes years. If you want to move from running the operation to directing it, you can explore our training on airports.
