The aircraft

The flight schedule of the airport is read from a pre-defined data table in Simio.

When the arrival time of each flight is reached, according to the schedule, a flight is created. Each flight has the following properties that are assigned to it:

• flight number

• flight type

• number of passengers

• arrival time

• departure time

• boarding time for departing passengers

7.1 The entities in the model

In the simulation model, the flights are numbered from one to the number of flights in the run, with the first flight being the one with the earliest arrival time.

The flight type is dependent on the size of the aircraft. The different sizes are:

• type A, where aircraft have a wingspan of 15 m

• type B, where aircraft have a wingspan of 29 m

• type C, where aircraft have a wingspan of 36 m

• type D, where aircraft have a wingspan of 52 m

• type E, where aircraft have a wingspan of 65 m

• type F, where aircraft have a wingspan of 80 m

In the model, the gates are numbered from one to 122. No gate can have the same number as another since it will then not be clear to which gate to direct the aircraft. However, the gates on either sides of each of the taxiways are numbered from one to 18 for those concourses with large gates and from one to 36 for those with smaller gates. This numbering of gates is important for knowing the position of each aircraft on the taxiway in order to prevent a collision of the aircraft. This concept is further explained in section 7.2.1. It is thus necessary that each gate has a property of its position on the taxiway. It is also important to know on which taxiway each gate is in order to know where each aircraft will leave the taxiways perpendicular to the concourses to enter the taxiway at which its gate is situated.

The model runs through all the gates and assigns the position and the taxiway of each gate to a one dimensional matrix. This is described by Algorithm 1.

Algorithm 1 Assign gate positions and taxiways For i = 1 to number of gates

position of gate(i) = Gate position (as read from table in Simio) taxiway of gate(i) = Taxiway of gate (as read from table in Simio) i ← i + 1.

end

7.1 The entities in the model

Once this is done, there is no need for the process to be repeated. By including the condition that it must be the first created flight in order to enter the loop described above, this step is only performed in the beginning of the simulation run.

After considering the above mentioned condition, each aircraft is assigned a priority. The first aircraft has a priority of one, the second of two and so on. The variable priority is assigned to the attribute aircraft.priority and then the variable priority is incremented. When the next flight arrives it will thus have a priority of one more than the previous. These priorities are then used as flight numbers. The flight type, representing the wingspan of the aircraft, is assigned to the aircraft in order to know which gates are suitable for it. This flight type is read from the table containing the flight schedule. As stated previously, in the new designs of Lanseria International Airport, there are three different gate sizes, small, medium and large. When a flight is created it has to be assigned to a gate. In this chapter the first and second rules of assigning flights to gates will be explained. The third rule will be explained together with the metaheuristic in chapter 11.

The first rule assigns the flight to the appropriate gate nearest to the main terminal building since all passengers have to go to that building to collect their luggage. In making this decision, the model starts at the gate closest to the terminal building. If the gate is currently occupied by another aircraft, the next gate is chosen. Once an available gate has been found, the model evaluates it to determine whether it is an appropriate gate for the flight in question. The gate is appropriate if it fits the size of the aircraft. If not, the next gate is evaluated.

The logic used in the model is described below:

• If the selected gate is a small gate, and the aircraft is small, the aircraft can be assigned to the gate.

• If the selected gate is a small gate and the aircraft is medium or large, the next gate is considered.

• If the selected gate is a medium gate, and the aircraft is small, the next gate is considered. This is done even though a small aircraft can park at a medium gate, because it may happen that a medium aircraft arrives at the

7.1 The entities in the model

airport with no suitable gates available, while small aircraft are occupying the medium gates. A small aircraft can be assigned to a medium or large gate only when there are no small gates available.

• When a medium gate is selected and it is a medium aircraft, the aircraft is assigned to the gate.

• If the selected gate is medium and the aircraft is large, the next gate is considered.

• If a large gate is selected, small or medium aircraft can only be assigned to it if there are no small or medium gates available. Again, this is done to prevent the situation of having no suitable gates available for the large aircraft.

• If a large gate is selected and the aircraft is large, the aircraft is assigned to the gate.

• If there are no suitable gates available for a specific flight, the aircraft has to wait. As soon as the first gate becomes available, it is tested to determine whether it is suitable for the aircraft in question. If it is, the aircraft is assigned to it. If not, the aircraft has to wait until a suitable gate becomes available.

In the second rule, a small aircraft is assigned to a gate of any size. Thus, if the available gate closest to the terminal building is a medium or large gate, the aircraft is assigned to it, even though there may be small gates available.

Similarly, if a medium aircraft arrives and the closest available gate is a large gate, the aircraft is assigned to it. In this rule, it may happen that a medium or large aircraft arrives without there being a suitable gate available while small aircraft are occupying the medium and large gates.

Once a flight is assigned to a gate, attributes such as the taxiway at which the gate of the aircraft is and the position of the gate on the taxiway are assigned to the aircraft. The condition of whether the arrival time of the aircraft has expired (i.e. whether the aircraft had to wait to be assigned to a gate) is tested. If the aircraft did have to wait, the waiting time is recorded. The total waiting time

7.1 The entities in the model

of all the flights will later be used as an output statistic to evaluate the airport layout.