AIM 

3/21/24 

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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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). 

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 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. 

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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), 

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Navigation Aids