background image

AIM 

6/17/21 

NOTE

 

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

re-

porting source for Automatic Dependent 
Surveillance – Broadcast (ADS

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

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

1

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

1

13.) 

1

2

10 

Performance

Based Navigation (PBN) and Area Navigation (RNAV)