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AIM

10/12/17

1

−1−3

Navigation Aids

of an

 

airport 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 RNAV 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 FAA 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.

1

−1−4. VOR Receiver Check

a.

The FAA VOR test facility (VOT) transmits a

test signal which provides users a convenient means
to determine the operational status and accuracy of a
VOR receiver while on the ground where a VOT is
located. The airborne use of VOT is permitted;
however, its use is strictly limited to those
areas/altitudes specifically authorized in the Chart
Supplement U.S. or appropriate supplement.

b.

To use the VOT service, tune in the VOT

frequency on your VOR receiver. With the Course
Deviation Indicator (CDI) centered, the omni

−bear-

ing selector should read 0 degrees with the to/from
indication showing “from” or the omni

−bearing

selector should read 180 degrees with the to/from
indication showing “to.” Should the VOR receiver
operate an RMI (Radio Magnetic Indicator), it will
indicate 180 degrees on any omni

−bearing selector

(OBS) setting. Two means of identification are used.
One is a series of dots and the other is a continuous
tone. Information concerning an individual test signal
can be obtained from the local FSS.

c.

Periodic VOR receiver calibration is most

important. If a receiver’s Automatic Gain Control or
modulation circuit deteriorates, it is possible for it to
display acceptable accuracy and sensitivity close into
the VOR or VOT and display out

−of−tolerance

readings when located at greater distances where
weaker signal areas exist. The likelihood of this
deterioration varies between receivers, and is
generally considered a function of time. The best
assurance of having an accurate receiver is periodic
calibration. Yearly intervals are recommended at
which time an authorized repair facility should
recalibrate the receiver to the manufacturer ’s
specifications.