General

The Tail Assignment Optimizer in N-OC Desktop is a tool used to assign flights to aircraft, either using simple assignment principles like ‘first in first out’/’last in first out’, or by optimization. 

There are several different predefined objectives the optimizer can work towards. For example, to make the aircraft follow the crew pairings, or to reduce unnecessary ground time for aircraft.

The tool can be used, either to move flights from ‘ghost’ aircraft to real ones, or to move around flights already assigned to aircraft in order to find a better solution.

The Optimizer can be set to follow, or ignore onward references, and multi leg flights.

Options for maintenance can be set so that the provided solution from the tail assignment optimizer makes room for maintenance checks after a specified number of days, flight hours, or landings.

Note: The Optimizer requires that VcRedist64 (2015-2019) is installed on the PC.

https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads

When you click the Wizard icon in the Schedule Gantt, the window opens. To get to the Tail Assignment Optimizer, click the first icon in this window, titled 'Tail Assign Optimizer'.

Load Data

The next screen concerns loading of data. 

Flights and aircraft can be loaded directly from the database by selecting the Load radio button, and entering the start and end of the desired period in the fields at the top of the window. 

Alternatively, the data already loaded in the Schedule Gantt can be used by the Tail Assignment Optimizer. For this option, select the Gantt radio button option in the as in the above image. 

Clicking the Next button will take you to the main window of the Tail Assignment Optimizer.

Note: The Gantt option loads the zoomed period, and the time is UTC.

Main window of the Tail Assignment Optimizer

 This page contains general settings which apply to all optimization algorithms.

Left Side of the Window

Note: If in the previous step, loading data from Gantt was chosen, then only leg filters and aircraft filters containing flights and aircraft already loaded in the Gantt will be applicable. If no filters are selected in this window, all legs and aircraft currently loaded will be included in the optimization.

Lower Part of the Window

In the lower part of the window, all legs currently loaded into the system are displayed. Each row corresponds to a flight. 

After a run is complete, the solution will be displayed in the Schedule Gantt, but will not be saved until the Save button in the Tail Assignment Optimizer window is clicked. 

Note: Saving results from the Tail Assignment Optimizer using the CTRL+S, or any other button in N-OC Desktop will not work, and that this button in the Tail Assignment Wizard must be used.

General Tab

Rotation Options

Results Options

Advanced Tab

This tab contains settings which affect the internal workings of the ‘min cost flow’ and ‘column generation’ algorithms.

Time Windows Tab

This tab contains settings for Time Windows used in the Column Generation algorithm. 

Time windows are used to speed up the optimization, and is needed to get a solution within a reasonable time frame (if the input data contains a large number of flights, or the period over which we optimize is long). 

Optimizing using Time Windows means that we divide the input period into smaller chunks, and we optimize over these shorter periods one after another. 

Note: The smaller the time window, the further the solution will be from the optimal one, but also the faster the optimization will be.

Column Generation and Integer Heuristic Tab

Under this tab are internal settings for the Column Generation algorithms.

Objective and Penalty Functions Tab

This tab contains settings for objective and penalty functions, which are used by the ‘min cost flow’ and the ‘column generation’ algorithms, to guide the solution away from what we want to penalize, and towards what we want to achieve.

Penalty Functions

Objective Functions

This sets the goal of the optimization. Several different objective functions are implemented in the system, and they are briefly described below.

Legality Rules Parameters Tab

This tab contains options to use some rules in the legality system in N-OC for the Tail Assignment Optimizer. Every rule which concerns a combination of a single flight and a single aircraft can be applied. This includes the ‘Restricted station rule’, in which the user can specify certain stations as forbidden for certain aircraft. 

Note: Rules that concern something different than ‘can aircraft A fly flight B’, cannot be handled by the Tail Assignment Optimizer in its present state.

The restricted stations parameters are created in the Rules Factory.

1. Dropdown contains all legality groups saved into the system.
2. Selecting a group in the dropdown and clicking ‘Show Rules’ displays the rules in this group in the left window.
3. You can here select one or multiple rules and move them over to ‘Rules To Use’, which will make the tail assignment optimizer consider these rules during a run, in that the solution it provides will not violate them.
   
   

Buttons	Descriptions
	Moves over every rule in the ’Available Rules’ window to the ’Rules To Use’ window.
	Moves over every highlighted rule in ’Available Rules’ to ’Rules To Use’.
	Moves over every highlighted rule in ’Rules To Use’ to ’Available Rules’.
	Moves over every rule in ’Rules To Use’ to ’Available Rules’.

Maintenance Tab

The Maintenance options in the Tail Assignment Optimizer works as such as the user defines maintenance checks which the aircraft must undergo. It is then specified on which stations and at what times these maintenance checks can be performed.

Checks Tab

In this tab, you can create maintenance checks which need to be performed on the aircraft.  Rules can be set up such that there is a limit on the maximum flight hours, the maximum number of landings, and the maximum time between two succeeding maintenance checks. You can also specify here for which aircraft types the check applies, and how long the maintenance check takes to perform.

To create a new maintenance check, click the Create New button. As can be seen in the figure, a new line appears where the different maintenance options for this newly created maintenance check can be entered. To delete the highlighted maintenance check, click the Delete button.

Stations Tab

In this tab, rules for each station can be set. For each station, you can specify the opening times during which maintenance can be performed, and also specify which particular maintenance checks can be performed.

To create a rule for a specific airport, select that airport in the dropdown then fill in the options on the right side panel. 

Results Tab

Under this tab, results from a successful run will be displayed. Under ‘General result’, results regarding the overall solution are shown. Under ‘Aircraft Result’, results regarding individual vehicles are displayed.

General Advice

• Different settings apply to different rotation options (or algorithms). For LIFO and FIFO, the parameters “Ignore onward”, “Ignore type”, “Ignore version”, “Ignore initial positions”, “Use estimated times”, “Ignore multileg connections”, and “Use fixed turn around time” will influence the solution.
• For Minimum cost flow, in addition to the parameters affecting the solution from LIFO/FIFO, the “objective function” and the “penalty for unassigned flights” will also affect the solution.
• For column generation, all parameter setting will affect the solution.
• If onward references exist for all flights, and you just want a solution which follows these references, it is sufficient to choose one of the faster Rotation Options (LIFO/FIFO/Min cost flow), and to uncheck ‘Ignore Onward’.
• After a successful run, the solution will be displayed in the Schedule Gantt, but will be saved first after the ‘Save’ button in the tail assignment wizard is checked.