The Airport Collaborative Decision Making (A-CDM) is an operational procedure of European origin that helps to improve the efficiency and punctuality of the airport, through the collaboration among the airport partners involved, with two direct benefits: a more effective predictability of events and optimized use of resources. These conditions allow all the stakeholders (airport operators, ground handlers, airlines, air traffic controllers, NMOC - Network Manager Operations Centre) to use top quality up-to-date unambiguous data.  In fact, all procedures and communication policies are standardized in order to reduce any possible source of error.
Each phase of the flight, from departure to arrival, is treated as a "single process" based on an information exchange platform, which is useful for optimizing air traffic management and service operations.
The A-CDM project is thus characterized by changing the operational methodology in "Turnaround" management: from "First come - First served " to "First ready - First Served".
In the context of pre-departure (Off-Blocks) sequence planning, the priority of A-CDM is to define the "Target Take Off Time" (TTOT) as accurately as possible in order to improve " en route” and “sector” planning by the European ATM; this process is accomplished through the activation of a series of DPI (Departure Planning Information) and "FUM" (Flight Update Messages) messages sent to NMOC. 
The Airport CDM can therefore be considered as the basis for linking the airport to the ATM system.
The Airport CDM has been implemented at the airport according to the five elements listed below:
1. Milestones Approach (Turn-Round Process)
2. Variable Taxi Time (VTT)
3. Collaborative Pre-Departure Sequence
4. CDM in avverse condizioni metereologiche
5. Collaborative Management of Flight Updates
The A-CDM procedure starts with the transmission of the ATC flight plan 3 hours before the EOBT (Estimated Off Block Time) and continues through 16 milestones that describe the progress of the flight in all its phases until take-off of the aircraft (ATOT - Actual Take Off Time).
The A-CDM is in fact an integrated platform that transfers real-time information on the progress of all departing flights to the NMOC, which forwards it simultaneously to the other connected airports. It is thus possible to benefit from interdependent and multilevel effects: optimization of air traffic flow, maximum utilization of airport capacity and related infrastructure, improvement in punctuality, reduction in consumption and, therefore, in environmental impact. 

Manuale A-CDM

A-CDM procedure in Naples Airport

 A-CDM basic glossary