What is the purpose of the VOR Minimum Operational Network (MON) for pilots without DME/DME equipment during a GPS outage?

1-1-8.
b. Most VORs are equipped for voice transmission on the VOR frequency. VORs without voice capability
are indicated by the letter "W" (without voice) included in the class designator (VORW).
c. The only positive method of identifying a VOR is by its Morse Code identification or by the recorded
automatic voice identification which is always indicated by use of the word "VOR" following the range's name.
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Reliance on determining the identification of an omnirange should never be placed on listening to voice
transmissions by the Flight Service Station (FSS) (or approach control facility) involved. Many FSSs remotely
operate several omniranges with different names. In some cases, none of the VORs have the name of the "parent"
FSS. During periods of maintenance, the facility may radiate a T-E-S-T code (-   -) or the code may
be removed. Some VOR equipment decodes the identifier and displays it to the pilot for verification to charts,
while other equipment simply displays the expected identifier from a database to aid in verification to the audio
tones. You should be familiar with your equipment and use it appropriately.  If your equipment automatically
decodes the identifier, it is not necessary to listen to the audio identification.
d. V oice identification has been added to numerous VORs. The transmission consists of a voice
announcement, "AIRVILLE VOR" alternating with the usual Morse Code identification.
e. The effectiveness of the VOR depends upon proper use and adjustment of both ground and airborne
equipment.
1. Accuracy. The accuracy of course alignment of the VOR is excellent, being generally plus or minus 1
degree.
2. Roughness. On some VORs, minor course roughness may be observed, evidenced by course needle or
brief flag alarm activity (some receivers are more susceptible to these irregularities than others). At a few stations,
usually in mountainous terrain, the pilot may occasionally observe a brief course needle oscillation, similar to
the indication of "approaching station." Pilots flying over unfamiliar routes are cautioned to be on the alert for
these vagaries, and in particular, to use the "to/from" indicator to determine positive station passage.
(a) Certain propeller revolutions per minute (RPM) settings or helicopter rotor speeds can cause the VOR
Course Deviation Indicator to fluctuate as much as plus or minus six degrees. Slight changes to the RPM setting
will normally smooth out this roughness. Pilots are urged to check for this modulation phenomenon prior to
reporting a VOR station or aircraft equipment for unsatisfactory operation.
f. The VOR Minimum Operational Network (MON). As flight procedures and route structure based on
VORs are gradually being replaced with Performance -Based Navigation (PBN) procedures, the FAA is
removing selected VORs from service. PBN procedures are primarily enabled by GPS and its augmentation
systems, collectively referred to as Global Navigation Satellite System (GNSS). Aircraft that carry DME/DME
equipment can also use RNA V which provides a backup to continue flying PBN during a GNSS disruption. For
those aircraft that do not carry DME/DME, the FAA is retaining a limited network of VORs, called the VOR
MON, to provide a basic conventional navigation service for operators to use if GNSS becomes unavailable.
During a GNSS disruption, the MON will enable aircraft to navigate through the affected area or to a safe landing
at a MON airport without reliance on GNSS. Navigation using the MON will not be as efficient as the new PBN
route structure, but use of the MON will provide nearly continuous VOR signal coverage at 5,000 feet AGL
across the NAS, outside of the Western U.S. Mountainous Area (WUSMA).
NOTE-
There is no plan to change the NAVAID and route structure in the WUSMA.
The VOR MON has been retained principally for IFR aircraft that are not equipped with DME/DME avionics.
However, VFR aircraft may use the MON as desired. Aircraft equipped with DME/DME navigation systems
would, in most cases, use DME/DME to continue flight using RNA V to their destination. However, these aircraft
may, of course, use the MON.
1. Distance to a MON airport. The VOR MON will ensure that regardless of an aircraft's position in the
contiguous United States (CONUS), a MON airport (equipped with legacy ILS or VOR approaches) will be
within 100 nautical miles. These airports are referred to as "MON airports" and will have an ILS approach or
a VOR approach if an ILS is not available. VORs to support these approaches will be retained in the VOR MON.
MON airports are charted on low-altitude en route charts and are contained in the Chart Supplement U.S. and
other appropriate publications.
NOTE-
Any suitable airport can be used to land in the event of a VOR outage. For example, an airport with a DME-required ILS
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approach may be available and could be used by aircraft that are equipped with DME. The intent of the MON airport is to
provide an approach that can be used by aircraft without ADF or DME when radar may not be available.
2. Navigating to an airport. The VOR MON will retain sufficient VORs and increase VOR service volume
to ensure that pilots will have nearly continuous signal reception of a VOR when flying at 5,000 feet AGL. A
key concept of the MON is to ensure that an aircraft will always be within 100 NM of anairport with an instrument
approach that is not dependent on GPS. (See paragraph 1-1-8.) If the pilot encounters a GPS outage, the pilot
will be able to proceed via VOR-to-VOR navigation at 5,000 feet AGL through the GPS outage area or to a safe
landing at a MON airport or another suitable airport, as appropriate. Nearly all VORs inside of the WUSMA and
outside the CONUS are being retained. In these areas, pilots use the existing (Victor and Jet) route structure and
VORs to proceed through a GPS outage or to a landing.
3. Using the VOR MON.
(a) In the case of a planned GPS outage (for example, one that is in a published NOTAM), pilots may
plan to fly through the outage using the MON as appropriate and as cleared by ATC. Similarly, aircraft not
equipped with GPS may plan to fly and land using the MON, as appropriate and as cleared by ATC.
NOTE-
In many cases, flying using the MON may involve a more circuitous route than flying GPS-enabled RNAV .
(b) In the case of an unscheduled GPS outage, pilots and ATC will need to coordinate the best outcome
for all aircraft. It is possible that a GPS outage could be disruptive, causing high workload and demand for ATC
service. Generally, the VOR MON concept will enable pilots to navigate through the GPS outage or land at a
MON airport or at another airport that may have an appropriate approach or may be in visual conditions.
(1) The VOR MON is a reversionary service provided by the FAA for use by aircraft that are unable
to continue RNA V during a GPS disruption. The FAA has not mandated that preflight or inflight planning include
provisions for GPS- or WAAS-equipped aircraft to carry sufficient fuel to proceed to a MON airport in case of
an unforeseen GPS outage. Specifically, flying to a MON airport as a filed alternate will not be explicitly
required. Of course, consideration for the possibility of a GPS outage is prudent during flight planning as is
maintaining proficiency with VOR navigation.
(2) Also, in case of a GPS outage, pilots may coordinate with ATC and elect to continue through the
outage or land. The VOR MON is designed to ensure that an aircraft is within 100 NM of an airport, but pilots
may decide to proceed to any appropriate airport where a landing can be made. WAAS users flying under part
91 are not required to carry VOR avionics. These users do not have the ability or requirement to use the VOR
MON. Prudent flight planning, by these WAAS-only aircraft, should consider the possibility of a GPS outage.
NOTE-
The F AA recognizes that non-GPS-based approaches will be reduced when VORs are eliminated, and that most airports
with an instrument approach may only have GPS- or WAAS-based approaches. Pilots flying GPS- or WAAS-equipped
aircraft that also have VOR/ILS avionics should be diligent to maintain proficiency in VOR and ILS approaches in the event
of a GPS outage.