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AIM

10/12/17

1−1−15

Navigation Aids

1−1−11. 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−up or repair and may be unreliable even though

intermittent or constant signals are received.

NOTE−

During periods of maintenance VHF ranges may radiate
a T−E−S−T code (

D DDD -).

NOTE−

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.

1−1−12. 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.

The voice communication is available on some

facilities. Hazardous Inflight Weather Advisory

Service (HIWAS) broadcast capability is available on

selected VOR sites throughout the conterminous U.S.

and does not provide two-way voice communication.

The availability of two-way voice communication

and HIWAS is 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.

1−1−13. User Reports Requested on

NAVAID or Global Navigation Satellite

System (GNSS) Performance or

Interference

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 undesir-

able 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 communi-

cations or NAVAID identification. GNSS problems

are often characterized by navigation degradation or

service loss indications. For instance, pilots conduct-

ing operations in areas where there is GNSS

interference may be unable to use GPS for navigation,

and ADS−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−B reports may stop receiving ADS−B position

messages and associated aircraft tracks.

In addition, malfunctioning, faulty, inappropriately

installed, operated, or modified GPS re−radiator

systems, intended to be used for aircraft maintenance

activities, have resulted in unintentional disruption

of aviation GNSS receivers. This type of disruption

could result in un−flagged, erroneous position

information output to primary flight displays/indica-

tors 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 for identification of these

disruptions and detect unexpected aircraft position

while monitoring aircraft for IFR separation.

b. Pilots reporting potential interference should

identify the NAVAID (for example, VOR) malfunc-

tion or GNSS problem, location of the aircraft (that is,

latitude, longitude or bearing/distance from a

reference NAVAID), magnetic heading, altitude, date

and time of the observation, type of aircraft

(make/model/call sign), and description of the

condition observed, and the type of receivers in use

(that is, make/model/software revision). Reports

should be made in any of the following ways:

1. Immediately, by voice radio communication

to the controlling ATC facility or FSS.

3/29/18

AIM