It is important to establish within your plans how you will detect the disruption to your PNT systems. For each of the risks you have identified, establish the method that will be used to determine whether this disruption is occurring. In order to detect a disruption, one must first understand what affects the disruption will exhibit in your specific systems or systems-of-systems. To do this, one must conduct a Failure Modes and Effects (FMEA) analysis that presents, in a controlled environment (in reality or simulation) all known PNT disruptions and how the system will react to each. Only in this way can one determine how to plan and develop mitigation strategies – as a minimum to alert the detection of the disruption (i.e., an alarm function), but ideally to implement actions that minimise or even preclude significant negative impacts.

Some disruptions will occur with a degree of forewarning, such as space weather events or vehicles moving into geographical areas containing permanent electronic interference. In these scenarios it may be preferred to activate your mitigation plans in advance of the expected encounter with the disruption to provide a given level of assured PNT, even if it is a degraded mode of operation.

An example outline sketch of a disruption indicator table for a fleet of delivery drivers is given below as an example. Note that in general the default detection mode is simply the absence of PNT data at the expected update rate.

Example disruption detection table for a fleet of delivery drivers serving a supermarket using a company-provided satnav for all navigation, planning and communication
	Disruption type
	Absence of PNT data at expected update rate	PNT system has lost power	Communication link lost	PNT device is suffering electronic interference
Indicator of disruption	Position is no longer updating on a moving map display.  Position accuracy is lower than expected and lower than required for normal operations.  Position information is wrong.  Time information is wrong.	Power light indication or electronic display is unlit	Error warning message  Loss of expected communication messages	PNT device may be displaying a related error, or may not be providing any PNT data at all.  Jamming might manifest as a lack of any data at all.  Spoofing or meaconing might manifest as incorrect position and/or time data.