Although the concept of Collaborative Decision Making (CDM) originated in the US, Europe did leapfrog ahead with its initiative called Airport CDM (A-CDM). A-CDM has been implemented at a number of European airports with varying degrees of success and it seems that the momentum of implementation has slowed somewhat. On the other hand, most everybody agrees that A-CDM, if done properly, does bring the benefits predicted by the early cost-benefit analyses.
While A-CDM has several elements, practically all the benefits arise from the shared information and resulting better decisions while the chief conceptual basis of A-CDM is embodied in the milestones approach. The milestones are in fact defined events and corresponding statuses that must be achieved at defined times as the flight is going through the turnaround process. The turnaround process is then managed proactively by all the parties involved who share the same view and understanding of the process and the consequences of not meeting a given milestone. In fact, the purpose of A-CDM is to make the operation more predictable which reduces unnecessary queuing at the runway.
Of course things did not stand still in the US either. While the basic principles of the A-CDM concept have been adopted it was necessary to steer developments in a direction that took account of the fundamental differences between Europe and the US environment. These concern mainly the more active role aircraft operators play in assigning and controlling airport resources like gates and ramp areas as well as the availability of the FAA Command Center which, unlike the CFMU in Europe, has real authority to dynamically manage the National Airspace System.
The FAA has developed a Surface CDM Concept of Operations which provides the overall framework for CDM implementation in the airport context, much like the A-CDM Concept of Operations does in Europe. Collaborative Departure Queue Management (CDQM) is one element of the Surface CDM Concept, which has actually been tested in the US (in Memphis among others).
As you will see in the next paragraph, under CDQM so called “aggregate departure allocations” are calculated for the aircraft operators with the purpose of:
• Ensuring constant delivery to the runway so that capacity is used to the maximum (in the presence of demand)
• Minimizing the waiting times at the runway (with due regard to minimum engine run-time before take-off power may be applied)
• Improving predictability
In essence, CDQM manages the length of the departure queue in a way that ensures that aircraft are kept waiting at the runway for the minimum possible time while the capacity of the runway is still used to the full. The inevitable delays occurring when demand exceeds capacity are moved from the runway to the gate/stand area. Instead of times for individual flights to meet at the departure runway, aircraft operators receive an allotment of slots to enter the movement area. The slots are allocated using the Generalized Ration by Schedule (GRBS) algorithm as specifically implemented for CDQM. The aircraft operators may use the entry slots without coordination with other aircraft operators or ATC. Once an aircraft enters the movement area in compliance with a slot assigned to it by the aircraft operator from its allocation, ATC takes over and controls the flight in the normal way.
Other than the reduction in queuing time at the runway, CDQM has the important effect of giving aircraft operators flexibility to rearrange flights within their allotted slot-set without having to coordinate with flow management or ATC. Of course not having to co-ordinate does not mean that ATC will not be informed of the sequence set up by the aircraft operator.
The best take-off sequence may be different from what the operators have come up with, based on their preferences in which case additional optimization may be required to ensure the best possible utilization of the runway. In all cases however CDQM provides a powerful additional means for aircraft operators to express their preferences and an opportunity for ATC and flow management to take those preferences into account.