summarise this:Chapter 7Gate Assignment
Introduction
The problem of the aircraft-gate assignment was defined with the introduction of gate walkways that connect passengers directly between the aircraft and the terminal area. Accordingly, each aircraft has to be allocated to one gate at the terminal. In the case that not enough gates are available, aircraft are parked at the apron and passengers are serviced by buses to connect to the terminal. The gate assignment problem is more significant at busy airports (hubs), where there are many arrivals and departures scheduled within a short time period over a limited number of gates. As mentioned earlier, at hub stations, the air carriers schedule time banks where a few flight arrivals are followed by a few flight departures to allow passengers to connect between different origins and destinations.
The gate assignment at the hub affects the walking distance of connecting passengers in the terminal, the baggage handling of connecting passengers, and cargo transfer, which directly impacts on the air carrier’s operating cost. For example, Figure 7.1 shows the trajectories of the connecting passengers and baggage of one flight arrival at a hypothetical airport terminal. It is clear that the total travel distance of the connecting passengers and the total transportation distance of connecting baggage depend on the location of the gate assigned to this flight. Proper assignment of the gates for each flight can optimize the connection time of passengers and baggage, and improve the overall turn time of aircraft at the terminal. This optimal gate assignment can contribute to the productivity of the aircraft and overall revenue to the airline.
There are several conflicting objectives for the gate assignment problem. First, gate assignment should increase the convenience of connecting passengers by minimizing the total walking distance. Furthermore, gate assignment should consider minimizing the total operating cost related to baggage and cargo handling, and the aircraft taxi distance. In addition, it should consider matching the aircraft size to the appropriate gate to account for the passengers’ seating capacity at the gate. Another consideration is aircraft assignment at adjacent gates: for example, two aircraft with long wings cannot occupy two adjacent gates at the same time. A further factor to be taken into account is schedule variability due to irregular operation conditions. So gate assignment should be sufficiently robust to minimize changes during irregularities. Figure 7.1 Example of trajectories of connecting passengers/baggage at airport terminal
The gate assignment problem is solved during the planning and operation phases of the schedule. At the planning level gate assignment should ensure that all flights can be accommodated by the gates available to the air carrier. During the operation phase, flights might need to be reassigned to other gates as a result of schedule irregularities due to flight delays and cancellations.
Problem Characteristics
Figure 7.2 gives an example of the aircraft assignment for a hypothetical set of gates. As shown in the figure, the solution to the gate assignment problem for each gate consists of a set of flight service times (aircraft turns) separated by periods of idle time at the gate. The turn time of an aircraft represents the difference between the departure time of a flight and the arrival time of its preceding flight at the gate. The idle time at the gate starts at the departure time of a flight and ends at the arrival time of its next flight at the gate.
The gate assignment problem is characterized as a non-deterministic problem and involves significant uncertainties that are related to the flight delays and cancellations. A delay to an outbound flight cause the aircraft to occupy the gate for a longer period than planned for this flight. Similarly, a delay to an inbound flight will also disrupt the assignment schedule at the gate. Furthermore, a cancellation of an outbound flight generates a need for an additional aircraft to be parked at one of the gates or near the terminal area, until a new assignment is given to this aircraft.
The gate assignment problem is also characterized as being time-critical during operation. During irregular operation conditions, a reassignment (recovery) plan needs to be rapidly formulated and disseminated quickly to the operators so that the passengers are informed about the gate changes, if any, in a timely manner. Figure 7.2 Example of the flight assignment for a hypothetical set of gates
Finally, the gate assignment problem is known to be combinatorial in nature, with many interacting decisions. The assignment of one flight to a particular gate affects the decision on which flight is to follow at this gate. It also affects the decision on which flight can be assigned to the adjacent gates, due to wing-length constraints for the corresponding aircraft.