The VOR Minimum Operational Network, the Two Hundred Stations the FAA Switched Off, and the IFR Backup Question Every Pilot Needs to Answer Before GPS Has a Bad Day
The FAA decommissioned roughly 270 VOR stations to build a GPS-independent IFR backup network - but it only works if pilots can still fly raw VOR approaches.
The FAA has deliberately reduced the United States VOR network from nearly 1,000 stations at its peak to approximately 688, engineered to provide a guaranteed GPS-free path to the ground anywhere in the contiguous 48 states. That structure is called the VOR Minimum Operational Network, or MON. It exists specifically for the moment GPS fails - and whether it works for any individual pilot depends entirely on skills that legal instrument currency does not require.
The VOR Network That Built American IFR Flight
VOR technology entered civil aviation in the 1950s and became the backbone of the entire IFR system. Victor airways connected transmitters across the country. Instrument approaches were built around ground stations. At its operational peak, the FAA maintained close to 1,000 VOR stations across the contiguous 48 states and Alaska, with enough density that a pilot at a reasonable cruise altitude might receive three or four stations simultaneously.
GPS eroded the operational need for that density. WAAS-based approaches with vertical guidance - LPV approaches - now outnumber every other approach type in the United States. The moving map became the primary reference for most instrument pilots, and VOR stations became expensive infrastructure for a function that satellite navigation was already performing better.
The FAA’s 2016 Decision: What It Kept and What It Cut
In 2016, the FAA published its formal plan for the VOR Minimum Operational Network. The question was direct: how many VOR stations does the country actually need? The answer was neither zero nor the existing count. It was a calculated 688 stations, retained specifically to meet one operational guarantee.
That guarantee: from anywhere in the contiguous 48 states, a pilot in a standard IFR-equipped aircraft can navigate using only VOR receivers - no GPS, no RNAV - to a landing at a MON-designated airport. MON airports are spaced within 100 nautical miles of each other. If the aircraft has VOR receivers and the pilot can fly a VOR procedure, the network guarantees a path to the ground.
To build that network, the FAA identified redundant coverage and scheduled it for decommissioning. Roughly 270 VOR stations have since gone dark. Victor airways through those stations were modified or eliminated. IFR en route charts today show a significantly thinned airway structure compared to charts from a decade ago - RNAV waypoints filling gaps where VOR fix after VOR fix once appeared.
Why This Matters Right Now: GPS Is Not Invulnerable
GPS jamming - deliberate interference that degrades satellite signals in a defined area - has affected civilian aviation during military training exercises and in specific geographic corridors. Jamming is at least detectable; the receiver notices degraded signal quality and flags the problem.
GPS spoofing is more serious. Spoofing involves transmitting false satellite signals that receivers accept as valid. The receiver reports a position. The moving map moves. The autopilot follows. And the reported position is wrong - sometimes dramatically so - with no warning flag because the receiver cannot distinguish false signals from real ones without external cross-checks.
This has become a documented operational problem in international corridors, particularly in regions of active geopolitical conflict. ICAO, EASA, and the FAA have all issued guidance on areas of known or suspected GPS interference. The practical defense against a spoofed GPS position is the same skill the MON presupposes: cross-checking GPS-derived position against raw VOR radials. A pilot who has tuned, identified, and is actively monitoring VOR receivers will notice when the radials disagree with the moving map. A pilot treating VOR as legacy equipment will not.
The Proficiency Gap the MON Exposes
FAR 61.57 instrument currency requirements do not specify VOR approaches. A pilot can satisfy the 90-day currency requirement flying RNAV approaches exclusively. Given that LPV approaches routinely offer 200-foot decision altitudes against VOR procedure minimums that may be twice that, there is rarely operational motivation to choose the VOR procedure when both are available at the same airport.
The NTSB has documented this drift in accident investigations involving unexpected equipment failures. Pilots who were current and properly certificated found themselves unpracticed on the specific skill the situation required. Legal currency and actual proficiency are not the same thing. The MON raises the stakes of that gap because the backup it provides only functions for pilots who can execute what it assumes.
Four Practical Steps for IFR Pilots
Know the MON airport symbol on IFR en route charts. Identify which airports in your regularly flown areas carry MON designation before you file, not after your GPS receiver fails at 8,000 feet in solid IMC. Those are your divert targets if satellite navigation becomes unavailable.
Know the VOR procedures at your regular airports and alternates - not just that a procedure exists, but the plate details: inbound course, final approach fix, minimum descent altitude, missed approach procedure. A procedure you have never reviewed cannot be flown reliably under pressure.
Keep your avionics database current. Decommissioned VORs remain in expired databases. Pilots have filed routes to stations that were switched off months earlier. In an IFR system where the underlying navaid structure is actively changing, an outdated database is a practical safety problem.
Practice raw data VOR approaches. Not RNAV approaches with a VOR tuned for reference. An actual VOR approach: intercepting the inbound course on the CDI, managing the descent using the plate, crossing the final approach fix, flying the missed, entering the hold. Under the hood with a safety pilot, or in actual instrument conditions. If that has not happened in the last several months, it belongs on the calendar.
Alaska Is a Different Calculation
The MON design standard applies to the contiguous 48 states only. Alaska operates under a separate navigation infrastructure calculus, driven by the density of remote airports, the criticality of instrument approaches to communities with no other reliable air access, and the terrain and reception geometry that differ substantially from the continental picture. The FAA has been considerably more conservative about VOR decommissioning in Alaska. Pilots operating there should treat navaid planning as a distinct study from what applies in the lower 48.
Key Takeaways
- The FAA retained ~688 VOR stations in the MON to guarantee a GPS-free path to the ground from anywhere in the contiguous 48 states, with MON airports within 100 nautical miles of each other.
- Roughly 270 VOR stations have been decommissioned since the program launched; current IFR en route charts reflect a significantly thinned airway structure.
- GPS spoofing - false signals that receivers accept without warning - makes VOR cross-checking a front-line defense, not just a backup drill.
- FAR 61.57 does not require VOR approaches for instrument currency; proficiency and legal currency are not equivalent.
- The MON’s guarantee holds only for pilots who can actually fly raw VOR procedures - the network was built, but using it requires maintained skill.
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