AIM 

4/20/23

 

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20

Navigation Aids

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11. NAVAID Identifier Removal During Maintenance

During periods of routine or emergency maintenance, coded identification (or code and voice, where applicable)
is removed from certain FAA NAVAIDs. Removal of identification serves as a warning to pilots that the facility
is officially off the air for tune

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up or repair and may be unreliable even though intermittent or constant signals

are received.

NOTE

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During periods of maintenance VHF ranges may radiate a T

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E

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S

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T code (

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D DDD

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).

NOTE

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DO NOT attempt to fly a procedure that is NOTAMed out of service even if the identification is present. In certain cases,
the identification may be transmitted for short periods as part of the testing.

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12. NAVAIDs with Voice

a.

Voice equipped en route radio navigational aids are under the operational control of either a Flight Service

Station (FSS) or an approach control facility. Facilities with two

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way voice communication available are

indicated in the Chart Supplement U.S. and aeronautical charts.

b.

Unless otherwise noted on the chart, all radio navigation aids operate continuously except during

shutdowns for maintenance. Hours of operation of facilities not operating continuously are annotated on charts
and in the Chart Supplement U.S.

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13. User Reports Requested on NAVAID Outages

a.

Users of the National Airspace System (NAS) can render valuable assistance in the early correction of

NAVAID malfunctions or GNSS problems and are encouraged to report their observations of undesirable
avionics performance. Although NAVAIDs are monitored by electronic detectors, adverse effects of electronic
interference, new obstructions, or changes in terrain near the NAVAID can exist without detection by the ground
monitors. Some of the characteristics of malfunction or deteriorating performance which should be reported are:
erratic course or bearing indications; intermittent, or full, flag alarm; garbled, missing or obviously improper
coded identification; poor quality communications reception; or, in the case of frequency interference, an audible
hum or tone accompanying radio communications or NAVAID identification. GNSS problems are often
characterized by navigation degradation or service loss indications. For instance, pilots conducting operations
in areas where there is GNSS interference may be unable to use GPS for navigation, and ADS

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B may be

unavailable for surveillance. Radio frequency interference may affect both navigation for the pilot and
surveillance by the air traffic controller. Depending on the equipment and integration, either an advisory light
or message may alert the pilot. Air traffic controllers monitoring ADS

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B reports may stop receiving ADS

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B

position messages and associated aircraft tracks.

b.

Malfunctioning, faulty, inappropriately installed, operated, or modified GPS re

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radiator systems, intended

to be used for aircraft maintenance activities, have resulted in unintentional disruption of aviation GPS receivers.
This type of disruption could result in unflagged, erroneous position

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information output to primary flight

displays/indicators and to other aircraft and air traffic control systems. Since Receiver Autonomous Integrity
Monitoring (RAIM) is only partially effective against this type of disruption (effectively a “signal spoofing”),
the pilot may not be aware of any erroneous navigation indications; ATC may be the only means available to
identify these disruptions and detect unexpected aircraft positions while monitoring aircraft for IFR separation.

c.

Pilots encountering navigation error events should transition to another source of navigation and request

amended clearances from ATC as necessary.

d.

Pilots are encouraged to submit detailed reports of NAVAID or GPS anomaly as soon as practical. Pilot

reports of navigation error events should contain the following information:

1.

Date and time the anomaly was observed, and NAVAID ID (or GPS).

2.

Location of the aircraft at the time the anomaly started and ended (e.g., latitude/longitude or

bearing/distance from a reference point),