As well as determining and documenting the planned responses of your organisation and system to the generic loss of PNT data, it is important to also compile and maintain a list of the different disruptions that can affect your PNT system. When it is possible to rapidly identify the cause of the disruption, it may be possible to then reduce the period of time that you are suffering the data outage by moving away from the disruption or by directly solving the issue.

For example, the following are typical risks for all systems:

• Power outages
• Loss of communication to required assistance or reference data
• Damage to an antenna, lens, mounting, cable, or other physical part of the system
• A software error resulting in a system crash or reboot
• Bad weather conditions occluding or degrading access to PNT information (e.g. camera visibility)
• Unintentional or intentional interference

Your system may have other risks to account for.

By compiling a list of risks that can cause PNT outages you can then design a testing suite to confirm the behaviour of the system during short and long outages. This then allows you to directly test the response to your system for PNT outages spanning, minutes or hours, and longer outages such as many days.

In some cases it will be possible to intentionally input incorrect data to your systems to simulate a PNT disruption.

The reader is highly encouraged to establish an annual PNT disruption testing day, similar to an annual fire drill, to safely test the behaviour of various subsystems (and ideally an overall system) when PNT data is degraded and when PNT is completely denied.

It is important to note that PNT disruptions can include the complete loss of PNT data, or a reduction in the PNT accuracy. In the case of reductions in accuracy, the level of integrity of the PNT system will determine if the PNT system correctly reports this degradation in performance. A low integrity system may report a much higher current accuracy in the data than is actually true. In a high integrity system the system should report the degraded performance and may also trigger an alarm if the data has dropped below the required level of performance for safe operation.