AIM
6/17/21
NOTE
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The U.S. government regularly conducts GPS tests,
training activities, and exercises that interfere with GPS
signals. These events are geographically limited, coordi-
nated, scheduled, and advertised via GPS and/or WAAS
NOTAMS. Operators of GPS aircraft should always check
for GPS and/or WAAS NOTAMS for their route of flight.
c.
GPS is a critical component of essential
communication, navigation, and surveillance (CNS)
in the NAS; and flight safety/control systems.
Additionally, some satellite communications avion-
ics use GPS signals for operations in oceanic and
remote airspaces. It is the sole aircraft position
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re-
porting source for Automatic Dependent
Surveillance – Broadcast (ADS
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B). Some business
aircraft are using GPS as a reference source for
aircraft flight control and stability systems. GPS is
also a necessary component of the Aircraft Terrain
Awareness and Warning System (TAWS) – an aircraft
safety system that alerts pilots of upcoming terrain.
There are examples of false “terrain
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pull up”
warnings during GPS anomalies.
d.
When flying IFR, pilots should have additional
navigation equipment for their intended route to
crosscheck their position. Routine checks of position
against VOR or DME information, for example,
could help detect a compromised GPS signal. Pilots
transitioning to VOR navigation in response to GPS
anomalies should refer to the Chart Supplement U.S.
to identify airports with available conventional
approaches associated with the VOR Minimum
Operational Network (MON) program. (Reference
1
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1
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3f.)
e.
When flying GPS approaches, particularly in
IMC, pilots should have a backup plan in the event of
GPS anomalies. Although the appropriate response
will vary with the situation, in general pilots should:
1.
Maintain control of the aircraft,
2.
Use the last reliable navigation information
as the basis for initial headings, and climb above
terrain,
3.
Change to another source of navigation, if
available (i.e., VOR, DME radar vectors).
4.
Contact ATC as soon as practical.
f.
Pilots should promptly notify ATC if they
experience GPS anomalies. Pilots should not
normally inform ATC of GPS interference or outages
when flying through a known NOTAMed testing
area, unless they require ATC assistance. (See
1
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1
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13.)
1
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2
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10
Performance
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Based Navigation (PBN) and Area Navigation (RNAV)