ESTABLISHING CRITERIA AND PRIORITIES FOR ASSESSING THE IMPACT OF REDUCED SEPARATION MINIMA ON AIR TRAFFIC MANAGEMENT
Konstantinos G. Zografos 1 Professor and Christos S. Tsanos Research Associate / PhD Candidate Transportation System and Logistics Laboratory (TRANSLOG) Department of Management Science and Technology Athens University of Economics and Business 47, Evelpidon St. & 33, Lefkados St., 113 62, Athens t: +30 210 8203673-5, f: +30 210 8203684, e:
[email protected] 1
corresponding author
Abstract Reduction of separation minima constitutes a viable alternative for accommodating the expected medium-term traffic increase in the European and U.S. airspace. The introduction of reduced separation minima has significant implications and impacts on a variety of dimensions of ATM system operation and merits further research. The objective of this paper is to present an integrated methodological framework for assessing the introduction of reduced separation minima in different flight phases of the ATM system (en-route, TMA, airport), considering multiple impact categories and the majority of stakeholders affected by the implementation of reduced separation minima.
Keywords Reduced separation minima, air traffic management, Analytic Hierarchy Process
1. INTRODUCTION
Major changes are required in Air Traffic Management (ATM) operations to accommodate the estimated growth of air traffic (predicted at 18.2% in Europe between 2005 and 2010 and at 27% in the United States by 2016) without compromising on safety issues (Eurocontrol, 2006; FAA, 2006). Currently a number of initiatives are being implemented for the enhancement of the capacity of the European ATM system without compromising on safety, e.g., a medium-term capacity enhancement plan for European airspace (Eurocontrol, 2006). The implementation of reduced separation minima (RSM) constitutes a viable alternative for accommodating the expected additional traffic while simultaneously taking into account the safe use of airspace and the respective infrastructure. The introduction of RSM has multiple and significant impacts on a variety of dimensions of ATM system operation (performance, safety, human factors, etc.) and merits further research. However, a large number of RSM are identified and proposed by numerous actors of the ATM system, such as organizations participating in ATM policy-making, research organizations etc. A detailed analysis of the multiple impacts of all proposed RSM on the ATM system is a very timeconsuming exercise, which moreover requires excessive resources. Therefore, there exists a need for a methodology for initial prioritization of RSM that will facilitate their subsequent detailed analysis in terms of the abovementioned issues. The objective of this paper is to present an integrated methodological framework for prioritizing and assessing the impact of RSM on the ATM system, which will take into account the following characteristics of the assessment problem at hand: i) multiple impact categories, ii) all flight phases (i.e., en-route, TMA, airport), and iii) majority of stakeholders affected by the implementation of RSM. The remainder of this paper is structured as follows. Section 2 presents the proposed methodological framework. Section 3 describes in greater detail the assessment method. Section 4 presents some preliminary results of the assessment, while Section 5 concludes.
2. METHODOLOGICAL FRAMEWORK
The characteristics of the assessment problem at hand determine the methodological steps required for handling said problem. At the outset, a literature review for the identification of the most important impacts of the implementation of RSM on the operation of the ATM system was undertaken. This review resulted in the identification of a set of impact categories and respective prioritization criteria which measure the impact categories (described in Section 3). This initial list of impact categories and prioritization criteria was reviewed in a workshop with the participation of ATM experts from Europe and the United States. The experts which participated in the workshop represented the majority of stakeholders affected by the implementation of RSM: national civil aviation authorities, international policy-making organizations, airport authorities, research organizations and industrial partners. An initial proposal of impact categories and prioritization criteria was reviewed by the experts and the final definition of the impact categories and criteria was achieved with their participation and
consensus. Following the definition of the impact categories and prioritization criteria, the workshop focused on their assessment in terms of their importance for the ATM system, which was made through the use of multi-criteria techniques and expert judgment (RESET, 2008). This process is described in greater detail in Section 3. The activity following the definition of the importance of the impact categories and prioritization criteria is the prioritization of the RSM in terms of the impact categories and criteria. The prioritization of the RSM is performed through the use of multi-criteria analysis. The process is described in Section 3. Following the prioritization of RSM and the analysis of the results, the RSM that are ranked highest (i.e., have the highest performance in terms of the impact categories and criteria) are selected for further detailed analysis in terms of safety, human factors, costbenefit assessment etc. The methodological framework is illustrated in Figure 1. Identification of characteristics of assessment problem
Literature review on impacts of implementation of RSM
Existing list of proposed reduced separation minima
Determination of impact categories
Selection of assessment criteria
Development of assessment instrument
Validation of assessment criteria with external experts
Activities described in the methodological framework
Are changes to assessment criteria required?
YES Re-definition of assessment criteria YES
NO Are further changes required?
NO Finalization of list of assessment criteria
Prioritization of impact categories and assessment criteria
Prioritization of RSM
Future activities Ranking of RSM in terms of the impact categories
Detailed analysis of RSM with highest ranking in terms of safety, human factors etc.
Figure 1. Methodological approach for assessing the potential implementation of reduced separation minima
3. IMPACT ASSESSMENT METHOD
Three major types of impacts of the implementation of RSM on the ATM system were identified in the literature: - Operational performance, which addresses the impacts of the implementation of RSM on ATM operations, - Environmental impact, which addresses the major environmental implications from the implementation of RSM, - Feasibility of implementation, which addresses issues related to acceptability, complexity and effort required for the implementation of RSM. Each of the proposed impact categories is measured through the use of a set of appropriately defined criteria used for the prioritization of RSM. The impact categories and the associated prioritization criteria are presented in Table 1. Specifically, Column 4 (“Applicable flight phases”) demonstrates in which flight phases a criterion is applied: Y (Yes) indicates that the criterion is applicable in the specific flight phase while N (No) indicates that the criterion is not applicable in the specific flight phase. Table 1. Impact categories and criteria for assessing the impact of reduced separation minima ID
Criterion
Definition
Impact category: Operational Performance Increase of the maximum number of aircraft that can be Increase of (airspace accommodated (into ATC sectors / in a given TMA / by an OP1 / TMA / airport) airport’s runways and taxiways) in a given time period, keeping capacity in mind aircraft separation and safety standards Decrease in (the difference between planned and actual Decrease of (en-route duration of the en-route flight phase / the duration of “hold” OP2 / TMA / airport) time before entering approach phase / the difference between delays planned and actual amount of time that an aircraft spends on the taxiway before take off) Increase of airspace Increase in the number of alternative flight levels and routes that OP3 flexibility can be used to accommodate aircraft requests Increase of ATM Decrease in the standard deviation of the duration of flights (in OP4 system predictability en-route / in TMA / in airport) Increase of flight Decrease of deviations from user-preferred horizontal and OP5 efficiency vertical trajectories (in en-route / in TMA / in airport) Impact category: Environmental Impact Reduction of fuel Reduction in the amount of CO2, H2O and NOx emissions per EI1 burn and emissions aircraft type (in en-route / in TMA / during take-off or landing) Decrease of noise Reduction in the level of noise emissions per aircraft (in TMA / EI2 emissions during take-off or landing) Impact category: Feasibility of Implementation Degree of institutional complexity of the implementation of Institutional FI1 RSM from the responsible institutional actors/authorities complexity participating in ATM policy-making Degree of political acceptability of the implementation of RSM FI2 Political acceptability by national and/or international political actors/authorities participating in ATM system management Degree of effort related to the implementation of reduced Implementation FI3 separation minima, including complexity of implementation, effort cost and timescale of implementation
Applicable flight phases En-route TMA Airport
Y
Y
Y
Y
Y
Y
Y
N
N
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
The selection of these impact categories and prioritization criteria was based on a review of the relevant literature (Hoffman et al, 2000; Majumdar et al, 2002; Creamer et al, 2003; and others) as well as extant studies on the assessment of impacts from the implementation of RVSM in European and U.S. airspace (Eurocontrol, 1998, 2001, 2002, 2003, 2004; FAA, 2001, 2003, 2006). Special consideration was given to the strategic performance objectives and targets for the European ATM system set forth by SESAR (SESAR, 2006), which are considered as a guide for all future ATM performance assessment initiatives and studies. The impact categories and prioritization criteria have been aligned with, or at least consider, the SESAR key performance areas that are applicable to the research problem at hand. It is important to note that major impact categories of SESAR, such as safety, human factors, cost-benefit assessment etc. are not evaluated in this phase of the assessment. This first phase of assessment of RSM considers only a subset of these impacts, with the remaining ones to undergo detailed analysis for those RSM that are assessed as having the highest positive impact on ATM operations. The assessment of the relative importance of the impact categories and criteria in terms of their impact on the ATM system requires a qualitative approach due to the following features of the problem at hand: -
A substantial number of stakeholders involved in and affected by the implementation of RSM, with different and sometimes conflicting objectives Multiple assessment criteria Inability to have hard figures for some of the considered criteria
A multi-criteria analysis technique (Analytic Hierarchy Process – AHP) has been selected for addressing the problem at hand. The AHP (Saaty, 1990) fulfils the following requirements: -
Considers multiple criteria Expresses the relative importance of the various criteria Compiles the approaches and opinions of various decision makers and identifies “compromise” solutions
In particular, the AHP provides a practical way to deal quantitatively with complex decision making problems which involve multiple decision-makers. The AHP has been previously used in ATM-related research, e.g., evaluation of the cost-effectiveness of a new ATM concept for Europe (Zografos and Giannouli, 2001). The goal of the Analytic Hierarchy Process model for the present needs is to assign relative importance to each of the impact categories and prioritization criteria. According to the AHP, a complex decision making problem is decomposed hierarchically into its components. Following, pairwise comparisons among the components are made, which express the relative importance of the components in a given level of the hierarchy (e.g., Level 3 – criteria) with respect to the elements in the level immediately above it (e.g., Level 2 – impact categories). The elicitation of the pairwise comparisons is made through expert judgment, while the AHP ensures the logical consistency of the responses. AHP hierarchies were constructed for the assessment of the impact of RSM in each of the three flight phases. An indicative AHP hierarchy (i.e., for the en-route flight phase) is illustrated in Figure 2.
ASSESSMENT OF REDUCED SEPARATION MINIMA FOR EN-ROUTE
Level 1: Goal
Level 2: Impact categories
Level 3: Criteria
Level 4: RSM
OP1
OPERATIONAL PERFORMANCE
OP2
OP3
ENVIRONMENTAL IMPACT
OP4
REDUCED SEPARATION MINIMUM 1
OP5
EI1
EI2
REDUCED SEPARATION MINIMUM 2
FEASIBILITY OF IMPLEMENTATION
FI1
FI2
REDUCED SEPARATION MINIMUM n
Figure 2. AHP hierarchy for the assessment of reduced separation minima for en-route
The planned final result of the assessment process is a ranking of RSM in terms of their performance with regards to the impact categories and the associated prioritization criteria (i.e., Level 4 with regards to Level 3 and Level 2). The current assessment process has resulted in the ranking of the impact categories and relative prioritization criteria in terms of the importance of their impact on the ATM system (i.e., Level 3 with regards to Level 2 and Level 1). This process was repeated for each of the three flight phases (en-route, TMA, airport).
4. PRELIMINARY RESULTS
As stated, the assessment of the relative importance of the impact categories and the respective prioritization criteria took place during the expert workshop described in Section 2. The assessment process was administered through the development of the appropriate expert-specific survey instruments and has catered for the subsequent analysis of results for the entire set of experts as well as per individual expert. While the analysis of the experts’ input is still underway, some preliminary results of the assessment of the importance of the impact categories are available and merit presentation. The ranking of the impact categories per flight phase is illustrated in Figure 3. Figure 3 shows that operational performance is considered as the most important impact category of the implementation of RSM for all flight phases, with feasibility of implementation in second place and environmental impact in third. It is worth mentioning that the relative importance of environmental impact is increased in the airport phase, since the impact of additional flights (stemming from the implementation of RSM) on the environment in the vicinity of airports is significant and constitutes a subject of discussion within the ATM and airport community. Feasibility of implementation is consistently important in all flight phases.
Relative importance of impact categories 60,0
Relative importance
50,0 40,0 30,0 20,0 10,0 0,0
EN-ROUTE
TMA
AIRPORT
Flight phase OPER. PERF.
ENV. IMPACT
FEAS. IMPL.
Figure 3. Comparative results of assessment of impact categories
The ranking of the prioritization criteria per impact category and flight phase is shown in Table 2. Table 2. Ranking of prioritization criteria per impact category and flight phase Flight phase En-route Impact category Operational Performance
Environmental Impact Feasibility of Implementation
TMA
1 - Increase of capacity 2 - Decrease of delays 3 - Increase of flexibility 4 – Increase of flight efficiency 5 - Increase of ATM system predictability 1 – Reduction of fuel burn and emissions 1 - Implementation effort 2 – Political acceptability 3 - Institutional complexity
1 - Increase of capacity 2 - Decrease of delays 3 – Increase of flight efficiency 4 -Increase of flexibility 5 - Increase of ATM system predictability 1 – Reduction of fuel burn and emissions 2- Decrease of noise emissions 1 - Implementation effort 2 – Political acceptability 3 - Institutional complexity
Airport 1 - Increase of capacity 2 - Decrease of delays 3 - Increase of ATM system predictability 4 – Increase of flight efficiency 5 - Increase of flexibility 1 – Reduction of fuel burn and emissions 2- Decrease of noise emissions 1 - Implementation effort 2 – Political acceptability 3 - Institutional complexity
Table 3 shows that for all flight phases, experts consider capacity increase and delays reduction as the most important operational benefits that will be brought about by the implementation of RSM, while the other three criteria are ranked in different positions in the three flight phases. The reduction of fuel burn and emissions is considered as the primary environmental benefit, while the importance of noise emissions decrease is higher in the airport phase. Experts also consider the effort required for the implementation of RSM (in terms of cost, timescale, complexity) is the most important issue determining the feasibility of implementing RSM. Political acceptability, a major issue for the implementation of new policies/measures, is ranked second while implementation effort comes third. 5. CONCLUDING REMARKS
This paper has presented an integrated methodological framework for the impact assessment of the potential implementation of RSM on the ATM system and preliminary results of the first step of its operationalization. Future activities involve: i) the prioritization of a set of RSM by external experts in a relevant workshop and, ii) further detailed analysis of the RSM that will receive the highest ranking in terms of safety, human factors and cost-benefit assessment. ACKNOWLEDGMENTS The work reported in this paper has been partially supported by the RESET (“Reduced Separation Minima”) research project, funded by the European Commission, Directorate General for Transport and Energy (DG TREN). REFERENCES Creamer, S., S. Entis and N. Haase, 2003. Reduced Vertical Separation Minima in U.S. airspace – Air traffic control issues and answers. Journal of Air Traffic Control, October-December 2003. Eurocontrol, 1998. Guidelines for the application of the ECAC Radar Separation Minima. European Commission, 2001. European Aeronautics – A Vision for 2020. Report of the Group of Personalities, January 2001, Office for Official Publications of the European Communities, Luxembourg. Eurocontrol, 2002. The EUR RVSM Implementation Project, Environmental Benefit Analysis. EEC/ENV/2002/08, 2002, Brussels, Belgium. Eurocontrol, 2003. Air Traffic Management Strategy for the Years 2000+, Volume 1. Available online at EUROCONTROL Validation Data Repository (VDR). Eurocontrol, 2004. The EUR RVSM Safety Monitoring Report, AFN-NAV-PER-SAF-001-2004, Brussels, Belgium. Eurocontrol, 2006. European Medium-Term ATM Network Capacity Plan Assessment 20072010, April 2006. Available online. Federal Aviation Administration, 2001. Aviation Capacity Enhancement Plan 2001. Available online. Federal Aviation Administration, 2003. Final Report For Domestic Reduced Vertical Separation Minima (DRVSM) Second Simulation, January 22, 2003, Washington, U.S.A. Federal Aviation Administration – Air Traffic Organization, 2006. Moving America Safely – 2005 Annual Performance Report, September 2006. Available online. Hoffman, E., J. Bellman, S. Grandperret and K. Zehgal, 2000. Traffic Analysis with Fast-Time Simulations to Evaluate Delegation Potentialities of Sequencing Operations. Proceedings of the 19th Digital Avionics Systems Conferences, 2000, Philadelphia, U.S.A. Majumdar, A., W. Ochieng and J. Polak, 2002. Estimation of European Airspace Capacity from a Model of Controller Workload. The Journal of Navigation, 55, 381-403. RESET Consortium, 2008. Methodological Approach for Prioritization of Reduced Separation Minima. Saaty, T.L., 1990. Decision Making For Leaders: The Analytic Hierarchy Process for Decisions in a Complex World, RWS Publications, Pittsburgh, U.S.A. SESAR Consortium, 2006. Air Transport Framework – The Performance Target. Deliverable 2, DLM-0607-001-02-00a, December 2006. Available online. Zografos, K.G. and I.M. Giannouli, 2001. Development and Application of Methodological Framework for Evaluating the Cost-Effectiveness of an Air Traffic Management System for Europe. Transportation Research Record, 1744, 52-64.
