# Pre-Departure Sequencer The optimization layer that sits on top of [[Airport Collaborative Decision Making]]. A-CDM gives you milestone tracking and information sharing. A PDS takes the next step: it actively sequences the departure queue to maximize runway throughput and minimize taxi-out time. The core problem: at a busy airport, 15-30 aircraft may be ready to depart in a given 30-minute window. The naive approach is first-come-first-served based on pushback request time. The smart approach: sequence departures based on runway configuration, wake turbulence separation requirements, departure route constraints, airline slot compliance, and real-time taxiway congestion. Reordering the queue by even a few positions can eliminate minutes of taxi waiting per aircraft. PDS takes the TSAT (Target Start-up Approval Time) from A-CDM and refines it into an optimized departure sequence. The TSAT tells you roughly when to start engines. The PDS tells you exactly when, accounting for the aircraft ahead of you in the queue, the separation required behind the aircraft currently rolling, and the taxiway routing options available. The direct outputs: reduced taxi-out time, improved runway utilization, fewer ATFM slot misses, less fuel burned on the ground. The indirect output: better predictability of TTOT (Target Take-Off Time), which feeds into network-level flow management through EUROCONTROL's Network Manager or the FAA's TFMS. PDS is the natural second module after A-CDM deployment. A-CDM provides the data foundation (accurate TOBT, ELDT, milestone updates from all stakeholders). PDS consumes that data to optimize the departure sequence. Without reliable A-CDM data, a PDS is optimizing on noise. The sustainability link is direct. Every minute saved in taxi-out time is fuel not burned and CO2 not emitted. See [[Airport Operations MOC#The Sustainability Link]]. Related: [[Airport Collaborative Decision Making]], [[Airport Operations MOC]], [[Aircraft Turnaround]], [[Constraint Programming]] --- Tags: #deeptech #firstprinciple