Definition
A method by which a navigation facility (such as a VOR, ILS, or GPS satellite system) checks its own signal accuracy and integrity using built-in equipment, and automatically removes itself from service or sends a warning flag to the cockpit if the signal falls outside tolerance.
Plain English
The navigation station watches itself. If something goes wrong with the signal it transmits, it shuts itself down or warns pilots, without anyone on the ground having to notice the problem first.
Context Anchor
Seen in instrument procedure material when discussing how ground-based navigation facilities are watched for accuracy and reliability.
Derivation
Internal' from Latin internus, meaning 'on the inside.' The monitoring happens inside the navigation facility itself, rather than being checked from somewhere else.
Why Pilots Care
It gives pilots confidence that the signal they are using is being watched for errors without needing constant manual verification.
Analogy
It is like a built-in warning system in a machine: the machine is not waiting for someone outside to notice a problem; it has its own check that can raise the alarm.
Intuition Check
Internal monitoring does not mean the pilot is monitoring something inside the airplane. Here, internal means the navigation facility has its own on-site checking system.
Example Sentence 1
The localizer's internal monitoring removed the signal from service when the course alignment drifted beyond limits.
Example Sentence 2
Internal monitoring allows the facility to remain in service only while signal parameters stay within FAA limits.