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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.