Conclusiones y proyecciones

Trivizas (1998) introduces a dynamic programming approach for solving optimally the static runway scheduling problem for landings and take-offs based on the CPS concept. The mixed-mode, segregated-mode, and multiple-runway environments are considered. His computational results obtained with actual traffic data and a real airport configuration show that even a modest value such as a maximum position shift of three can increase the runway capacity up to 20% compared to FCFS sequencing.

Bianco et al. (2006) introduce static and dynamic models for scheduling the land-ing and take-off of aircraft in the terminal manoeuvrland-ing area (TMA). The pro-posed deterministic job shop scheduling model can represent several operational constraints and different runway configurations. The model considers the runway, TMA, inbound and outbound flight paths, holding stacks for landing and hold-ing points for take-off. The solution method is based on a fast descent heuristic.

Experimental results using real data of Milan Malpensa and Rome Fiumicino air-ports show that the average delay can be reduced by more than 40% and the TMA capacity may increase up to 30% in comparison with FCFS sequencing.

4.4 Remarks

Predictions for increasing air traffic over the next 15 years puts pressure on air navigation service providers around the world to improve safety levels, reduce delays, and cut the costs. This is the motivation behind the SESAR (Single Eu-ropean Sky ATM Research) and NextGen (Next Generation Air Transportation System) programs. SESAR is a European air traffic control infrastructure mod-ernization program that aims to eliminate the fragmented approach in European air traffic management, to transform its system, to synchronize all stakeholders, and to federate resources (EUROCONTROL, 2012). NextGen is the transforma-tion of the entire air transportatransforma-tion system through the use of twenty first century technology to support the current and future demand for aviation services in the

46 Chapter 4 Literature Review United States (FAA, 2012). After reviewing previous research studies on ALP and ATP and observing air traffic controllers in a working environment, we would like to highlight some of our findings. In our research, we aim to fill some of these gaps.

Practical vs theoretical models

As explained before, many theoretical studies may show an increase in utilization of the runway capacity, but it may not be possible to implement the models in practice. Often, some critical operational constraints in the modelling are ignored, some of the hard constraints in obtaining a solution are relaxed, or required com-putational resources are unreasonable.

Quick and good vs slow and optimal solution methods

In real situations, controllers can only use algorithms which can quickly (in a mat-ter of seconds) find a good solution (near-optimal). Optimal solutions arising from lengthy computation times are of little practical use.

Defining the objective functions and constraints

Choosing an appropriate objective function for the ALP/ATP is controversial and stakeholders (air traffic control, airports, airlines, and government) may have con-flicting criteria. Thus, selecting one or more objective that can satisfy the interests of all parties, or provide an acceptable compromise, is an important first step to-wards the model to be implemented.

Robustness and flexibility

There are different levels of uncertainty associated with the information considered within an ATP/ALP, especially in a dynamic environment. The uncertainty can be caused by weather conditions such as winds and snow, the precision of equip-ments, as well as the uncertainty in pushback times and taxi times for departing aircraft. However, most studies consider a static rather than a more realistic dy-namic environment.

Increasing the number of separation categories

Currently, ICAO classifies aircraft into three categories of Heavy, Medium and Light. Since wake vortex separation is a primary constraint on runway through-put, refining the classification into more classes may increase runway capacity.

Integrated models

There are several models that can relatively solve problems involving individual components of airport operations effectively. However, a major challenge is to form an integrated model. Possible types of integration include integrating run-way scheduling, ground movement control, and gate assignment. Another example is the scheduling of an aircraft’s take-off and landing at the same time which re-quires runways at several airports to be scheduled simultaneously.

Throughput is the primary objective for ATC

The literature considers many different objective function criteria, whereas in gen-eral controllers are only concerned with throughput after safety considerations are taken into account. In order to balance other criteria, controllers need more infor-mation and good decision support tools to use this inforinfor-mation.

Availability of information in advance

The accuracy and timeliness of information can improve decision making. One of the purposes of the Collaborative Decision Making (CDM) approach for airports is to provide relevant information to all parties (airport, airlines, and ATC) in ad-vance. This helps controllers to schedule landings and take-offs with better insight into the future state of the system.

US vs Europe

There are greater research activities in airport runway scheduling in the US com-pared to Europe. The difference in the type of research on the ALP and ATP in the US and Europe indicate that joint research projects would provide a good opportunity for both communities to enhance their models and further develop their solution algorithms.

48 Chapter 4 Literature Review In the next chapter, the ALP has been defined in details and different solution methods for scheduling arrival flights to the airport have been discussed.