This model is a simple representation of the logistics system in place to maintain an aircraft fleet at a number of Airfields. It concentrates on the repair and re-supply of a key navigational aid that has a selected failure profile. The model offers the options to hold dedicated local stocks of these navigational aids or to operate a common store from which refurbished aids are dispatched when the one spare that is held at an airfield is needed.

With the model it can be evaluate whether it is better to hold these stocks locally or centrally. Key statistics include the number of navigational aids in the system (and hence cost) and the resulting "up" time or flights that are not delayed due to a lack of operational parts.

Both the operational performance statistic for each airfield and the levels of equipment waiting repair are shown in selected windows

This model illustrates the modular nature of WITNESS and the ability to reuse large parts of models again and again. To introduce a fourth airfield into the model simply select one of the airfield modules in the element selector and use the right mouse button to clone the module. Place it on the screen, rename it if you like and run the model again. The fourth airfield is automatically linked into whole operating rnodel (including the statistics).

The model also illustrates the use of dialog boxes in WITNESS to interact with the user. For an example of this please look in initialize actions from the model menu.

To see the model logic clearly it is best to run this model with the walk option turned on.
 

The attached video shows the behaviour before mentioned.