Definition
A reduced network of VOR ground stations retained by the FAA to provide a backup navigation capability if GPS service is lost or degraded. The MON is designed so that an aircraft anywhere in the contiguous United States, at or above 5,000 feet AGL, can navigate by VOR to a suitable airport within 100 nautical miles for an instrument approach.
Plain English
As the FAA decommissions VORs no longer needed in a GPS-based system, it keeps a smaller core set of them in service as a safety net. If GPS fails, pilots can still use these remaining VORs to reach an airport and land using a non-GPS instrument approach.
Context Anchor
Seen in discussions of IFR navigation, GPS outages, FAA navigation planning, and the gradual reduction of older ground-based navigation stations.
Derivation
Minimum Operational Network describes exactly what it is: the smallest network of VOR stations the FAA considers operationally sufficient to back up GPS. The phrase signals that this is a deliberately trimmed-down, not a full, network.
Why Pilots Care
It guarantees a fallback navigation capability so IFR flight can continue safely during GPS disruptions.
Analogy
Think of it like keeping a basic set of paper maps in the airplane even if you normally use a tablet. You may not use them every day, but they matter when the main system is not available.
Intuition Check
Minimum does not mean optional or unimportant here. It means the smallest VOR network the FAA believes is needed to provide a usable backup navigation system.
Example Sentence 1
After GPS coverage was lost in the area, the pilot used a MON VOR to navigate to the nearest suitable airport and fly the ILS approach.
Example Sentence 2
Pilots planning for a GPS failure checked the Vor Minimum Operational Network coverage on their route.