HISTORICAL PERSPECTIVE
The concept of Collaborative Decision Making (CDM) was originally defined in the United States by a group of airlines, led by US Air, in response to what the airlines perceived as inadequate co-operation between airports, the FAA and the airlines themselves. They formed the so called CDM Group, members of which visited several airports with traffic flow problems and analysed the reasons.
Significantly, they discovered that in many cases the reasons were in fact quite trivial. In one case, a missing telephone connection between the FAA tower and the Delta ramp controller was found to be at the root of major departure delays; in another case the “secret” nature of cancelled flights was found to be the cause of unused slots at an otherwise seriously congested airport.
The CDM Group in its original reports had actually established three of the most basic rules of CDM which remain valid to this day even if, unfortunately, in some cases they are being ignored. The three rules are:
• Most problems have simple causes with simple solutions
• Better information sharing eliminates a very large proportion of the problems
• CDM can only be successful if trust is established between the partners as the first step
Although the CDM Group did at first address problems at airports (Atlanta and Philadelphia) when the FAA embraced the concept, they focused on applying it in the en-route environment. This was a natural consequence of the US scene where capacity constraints were present en-route while airports were almost all free flow at the time. Nevertheless, US airports got involved in CDM early as a result of the FAA’s ground-delay concept. The value of information sharing was shown right from the start. Just by being better informed, airlines were able to respond to the restrictions in a much more efficient manner. The initiative in the early 1990s called FAA/Airline Data Exchange (FADE), supported among others by Northwest Airlines, can be seen as the direct forerunner of what evolved into the US CDM project of to-day.
The CDM concept was brought to Europe by experts of IATA and at first it was treated as a research topic and as such, assigned to the EUROCONTROL Experimental Centre. Several years passed and the concept was stuck on the research agenda while the need for better decision making grew every day. At the time, also in Europe most of the delay problems had their origins in the en-route environment and of course the power of CDM could have brought the same level of relief as it did in the US if only States had gotten together and implemented CDM. But this did not happen in spite of repeated pleas by the airspace users.
The lack of progress did not go unnoticed by EUROCONTROL and following a suggestion by IATA they came up with a new idea. Even if it was proving very difficult to get European States to embrace CDM in the en-route context, the more independent and business minded airports, with their more or less closed systems and multiplicity of partners, might prove more receptive to improved decision making and hence introducing CDM on the airport level might prove to be actually feasible. This is how Airport CDM (A-CDM) was borne.
In recent years of course airports in Europe have become a major source of delay and hence A-CDM was proven to be a good idea in more sense than one. But all development projects must keep in mind that A-CDM is not special at all, it is simply a pragmatic sub-set of CDM implementation forced by the initial failure of getting CDM on-board in the en-route context.
Not that A-CDM was an immediate hit. Although many airports created CDM teams, built systems and even booked some initial results, full, across the board exploitation of CDM remains the exception rather than the rule.
An important, relatively recent development of course is the realisation that individual airports forming “CDM islands” can only achieve
limited benefits if the air traffic management network of which they are a part is not fully involved. Bringing the Central Flow Management Unit (CFMU) into the CDM picture was a major step in CDM implementation in Europe and the first one in realising what one may call “network CDM”.
Needless to say, CDM is an important element in the operational concept of both the European SESAR program and NextGen in the US. Under these initiatives, all decisions will be required to be collaborative to the maximum extent possible and hence the idea of CDM will be influencing the very core of air traffic management practice at every level.
CDM APPLICATIONS IN THE US AND EUROPE
EUROCONTROL and the FAA actively cooperate on many aspects of CDM. There are several European ideas and procedures that are being considered for inclusion in the US CDM projects, among them the better utilisation of Target Off-Block Time (TOBT) and next day planning. The US CDM project has several sub-teams and they manage a range of CDM sub-projects, most of which are specific to the integrated US air traffic management environment. It is important to note that the US CDM projects can benefit from a lot of information sharing functionality already available in the FAA’s systems. These capabilities are being delivered by the US System Wide Information Management (SWIM) program which has as its main task the data level integration of the legacy systems as well as the new system elements being implemented.
A lot of the US CDM activity is dealing with items that in Europe would fall under the purview of the CFMU. Examples are the Integrated Collaborative Rerouting (ICR), Airspace Flow Program (AFP) or the Unified Ground Delay Program (UDP). Others, like the integration of the Traffic Management Advisor (TMA) and the Flight Schedule Monitor (FSM) or the Control by Time of Arrival (CbTA) concept are more on the control centre level.
The US CDM scene is also influenced to a large degree by the initiatives taken by some airlines to improve their own operations. This is a US peculiarity mainly because there is no comparable operational density anywhere in Europe. The Surface Management Systems (SMS) used by UPS in Louisville and by FedEx in Memphis hold a lot of important lessons that can be utilised also at other airports.
CDM in the USA can be seen as encompassing the whole operation and is not split into clearly identifiable elements like airport CDM and network CDM. This is not surprising if we consider that creating A-CDM in Europe was an artificial division to begin with.
In Europe, CDM is currently instantiated in the form of clearly defined concept elements which are in fact applications that can be realised in software also. They cover areas where a shortcoming had been identified and are meant to directly address those shortcomings. In this way, we have CDM Information Sharing (the basis for everything else), Variable Taxi Time Calculation but also Collaborative Flight Data Update which is in fact a network CDM elements bringing the CFMU into the picture.
Unfortunately, information sharing in Europe is still in its infancy and the only real islands of SWIM-like activity are the airports even if the information sharing practiced there is local and a far cry from the flexible information sharing envisaged by the SWIM concept. Nevertheless, airport level information sharing has shown conclusively the power of shared information to improve decisions across the board.
Needless to say, the CFMU has several tools used to establish network demand and capacity and to influence both. They do interact with both the users and the providers but their activity is not fully recognised as part of the CDM concept. This should change however as the CFMU moves progressively from a prescriptive to collaborative approach to flow management.
CDM APPLICATION BENEFITS
In 2007-2008, EUROCONTROL had commissioned the production of CDM CBAs for Barcelona, Zurich, Brussels and Munich. At the time, also a generic CBA was produced, taking a typical EUROPEAN airport as the baseline. In 2008, a CDM CBA was also ordered for Prague.
Originally it was the intention to show the benefits of CDM in general but also the specific benefits attributable to the different CDM applications, like information sharing, variable taxi time calculation and so on. This was meant to enable planners to set implementation priorities and find the best possible combination of applications for any given airport. At that time there was no airport where all the applications had been implemented and so some of the work had to be undertaken using projections and well reasoned assumptions based on interviews with operational experts.
The conclusions were predictable and not at all surprising as they lined up perfectly with the most basic tenets of the CDM concept. In excess of 90 % of the benefits attributable to CDM were in fact generated by information sharing. Other applications added only small, incremental improvements and the order of implementation was also of little impact on the actual benefit picture. It was therefore not possible to really quantify the benefits of applications, or combinations of applications, beyond information sharing as the additional improvements were well within the error range of the calculations.
Although EUROCONTROL has started to promote a more prescriptive approach to CDM in recent years specifying the implementation order of CDM applications, the fundamental benefit balance of those applications has not changed.
A new feature of CDM of course is the network version where several airports start to collaborate with each other and the CFMU using information sharing and the other applications. This kind of network CDM forms the basis of the SESAR concept of operations also.
In this context we must remember that information sharing as defined for CDM is in fact an early instantiation of the System Wide Information Management (SWIM) concept and at some point SWIM will overtake this aspect of CDM. The benefits will not diminish since support for decision making and the current and future CDM applications will of course continue.
THE SCOPE OF CDM
Because in Europe only airport CDM has made significant progress so far, the best indicator for the scope of CDM as currently practiced is the “milestone approach” CDM application. In this application, the milestones are selected along the timeline representing an aircraft’s progress through the ATM network. Although the milestones are often depicted in a linear manner, they may in fact belong to processes concerned with the flight that run parallel with each other. Some of the processes may also be only indirectly related to the main timeline.
Studying the milestones defined for A-CDM as we currently know it reveals that the CDM scope represented by them is concerned exclusively with the air-side operations of the airport and even there, the scope is restricted to services/processes in the close surrounding of the aircraft concerned. This is perhaps not surprising since analysis of a wider surrounding and especially the land-side operations would probably have been too complex in the initial phases of the European CDM projects.
It is also evident that the turn-round phase of flight is included in the current scope. An aircraft’s trajectory, while it is on blocks at the gate or at a remote stand is in a peculiar status. One may say it is “idling” with only its time dimension evolving, the spatial dimensions not. However, the trajectory continues to consume resources and numerous milestones may be defined to track its evolution in time.
If the CDM scope is kept relatively narrow (air-side only, close in to the aircraft only), the resulting milestones will not capture several important factors which in fact have a direct influence on the idling trajectory. Consider the following. While the aircraft is in the air or taxiing to its stand, its current trajectory is not affected at all by land-side processes, overlong security queues or missing baggage. Once the aircraft is at the gate, processes not currently considered by CDM will suddenly have a direct influence on the idling trajectory, changing its evolution through time. The earlier these influences are known and the better their visibility, the more predictable the trajectory will become and hence the higher the benefits will be.
Most of the processes involved in the turn-round have been studied in the past and while there is still scope for their optimisation, the possibilities for further gains are limited. What has not been studied are the hitherto invisible processes and influences that fall outside the current CDM scope. Most experts agree that very real additional benefits can be generated by looking at the turn-round with a scope that is wider than what is currently the norm.
It is well known that at the time of writing, there is still no general agreement on whether or not A-CDM should be looking at passenger handling related processes and land-side operations with several schools of thought present, neither with a decisive majority. This is regrettable because the influence of some of the hitherto unconsidered processes cannot be denied. It is also an opportunity to introduce novel elements into the A-CDM scope.
CDM AND THE EUROPEAN COMMUNITY SPECIFICATIONS
Community Specifications provide an appropriate means (of defining the technical and operational conditions necessary) to meet the Essential Requirements and relevant Implementing Rules for interoperability though a community specification is not formally required in order for an IR to apply.
Community Specifications foreseen by the Interoperability Regulation are either:
– European standards for systems or constituents, drawn up by the ESOs (CEN, CENELEC, or ETSI) in cooperation with EUROCAE; or
– Specifications drawn up by EUROCONTROL on matters of operational coordination between ANSPs.
The standards drawn up by the ESOs are initially produced as European Standards (ENs). The ENs and the EUROCONTROL Specifications only become Community Specifications once the references to them are published in the Official Journal of the European Union. The following diagram illustrates the relationship between the Community Specifications, the Implementing Rules, and the Essential Requirements.
Compliance with Community Specifications is voluntary. However, compliance with published Community Specifications creates a presumption of conformity with the Essential Requirements and with the relevant Implementing Rules.
Conformity with the Essential Requirements and with the relevant Implementing Rules may be achieved without a Community Specification, where appropriate other means of demonstrating conformity can be provided by ANSPs or manufacturers.
Airport Collaborative Decision Making is the subject of a Community Specification under the Single European Sky Interoperability Regulation EC 552/2004. The A-CDM Community Specification has been developed by the European Telecommunications Standards Institute (ETSI) in cooperation with EUROCAE to guide compliance with the Essential Requirements of the Single European Sky Interoperability Regulation and as applicable with the implementing rules in the same regulation.
The end of the public enquiry for the CS was 17 December 2009 and the planned date of publication in the Official Journal of the EU is 27 September 2010.
Although every requirement in the CS is referenced to EUROCONTROL and EUROCAE documents (which were in turn developed with the full participation of European CDM experts), the CS has raised some concerns, mainly by certain airports.
While the need to standardise certain elements of CDM is not in question, the rather rigid rule making seen in the CS has raised fears about how necessary changes will be handled on the one hand and how the nature of CDM would change as a result of what some see as too extensive regulation. This is the case even though compliance with Community Specifications is voluntary. However, since compliance with published Community Specifications creates a presumption of conformity with the Essential Requirements and with the relevant Implementing Rules, the fear exists that there will be too much pressure to comply regardless of how financially sound this may actually be.
A CS can be changed if necessary although there is a procedural overhead. Updates and amendments to a CS are handled by the working structure established for the corresponding field and in accordance with the requirements of the change or amendment. Once a change or amendment has been agreed, it has to be adopted by the Single Sky Committee. Thereafter it takes 3-6 weeks before the change or amendment is published in the Official Journal of the EU. The cause for concern is obviously the time that may be required before the material is submitted to the SSC.
This regulation based approach to CDM is one of the major institutional differences between Europe and the US. In the latter CDM remains a voluntary, collaborative process seen by many as more in line with the original CDM concept. At the time of writing it is not yet clear which approach will prove more effective in the end.
CDM AT EUROPEAN AIRPORTS
According to the European CDM web-site, 30 European airports have a CDM project running. Their maturity is very diverse and ranges from early plans through project definition activities to full fledged A-CDM, meeting almost all of the EUROCONTROL functional requirements.
While it was possible to develop a positive cost-benefit analysis for all the planned or actual projects, the most convincing information is available from Munich, the only airport so far with a truly advanced, complex and operational CDM set-up based on the EUROCONTROL A-CDM requirements and which has been in operation without interruption since 7 June 2007. It is interesting to note that even Munich has not followed the original functional requirements to the letter. They have made a few minor changes where those appeared necessary and as such have collected important insights into where the requirements may need to be changed or made more flexible to maximise the benefits for a given local environment without adversely effecting interoperability.
Munich had a very comprehensive set of targets and the results for 2008 (the most recent full year for which data were available at the time of writing) show that basically all targets were met or exceeded. This represents a net overall improvement in the operation of Munich airport as seen from the airspace user perspective. The Munich report notes also that the improved data exchange with the CFMU that had been undertaken by several airports resulted in a reduction of delays, clearly showing the network benefits of CDM.
The Munich CDM operation does have as one of its targeted benefits optimised turn-round times and the more efficient use of airline/handling agent resources, however, it does not have specific focus on turn-round as such. The scope of CDM in Munich has also been kept to within the traditional limits.
It is not unreasonable to conclude that Munich has pushed the A-CDM benefits close to their maximum potential using the traditional scenarios. Additional improvements will probably need expansion of the CDM scope.
Finally, it is important to note that according to a number of airlines, A-CDM seems to work well in normal operations but problems do arise when weather or other similar issues create a disruption. Clearly, more work is needed to address this phenomenon.
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