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NON-DIRECTIONAL

BEACON

NDB

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GROUND BASED EQUIPMENT

NDBs are rarely found in the US, But still

common in Canada. Used in busier areas as a means of identifyingapproach fixes (ILS), and as a sole means of

navigation and approach in remote areas.(unless equipped with GPS)

NDB facilities are relatively inexpensive to build

and maintain. NDB simplicity is its greatest strength.

Essentially an AM radio transmitter.

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AIRCRAFT EQUIPMENT

Receiver

Control Head

Indicator(Automatic Direction Finder) Fixed Card relative bearing

Rotatable Card magnetic bearing

Radio Magnetic Indicator (RMI) magnetic bearing

The head of the needle always points to the station.

Two Antennas Sense non-directional signal Loop directional signal (180 ambiguity without

sense)

Note: see propilot simulation

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OPERATION

The desired frequency is tuned.

The station is identified.

ANT setting may be used to identify station, butno directional information will be available, ADFmust be selected prior to navigation.

ADF equipment has no flag system to indicatereception, therefore pilots must monitor theaudible identifier of the station anytime ADF is

the sole means of navigation and throughout theapproach phase of flight. Note: some EFIS displays incorporate a flag warning

system, making audio monitoring unnecessary.

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SELKIRK AVIATION SOP 2.8.11

Monitoring ADF Audio

When IFR or simulated IFR and navigating by ADF,the ADF audio identifier will be monitored during all

NDB instrument departures and approaches. When

navigating enroute with ADF only, pilots should check

the Morse code identifier frequently to confirm the

station is still working.

When flying GPS overlay approaches that have been

properly setup from the database it is not necessary

to monitor ADF audio.

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ERRORS

Bank Error needle will point down to thestation when aircraft is banked.

Quadrantal error Caused by therefraction (bending) of the incoming radiowaves by the aircraft structure.

Minimum when station is off cardinal points(nose, tail, or wingtip).

Maximum in between.

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LIMITATIONS

Skip Zone: an area of erratic indication or signalloss between the points where the ground wave

ends and the sky wave hits the ground. Night Effect: occurs at night due to the

reception of sky waves reflected by the

ionosphere. It is most pronounced at sunriseand sunset. Has a greater effect on higherfrequencies. More pronounced further from thestation.

Fading: similar to night effect although theerratic indications are caused by out of phasesignals. Usually results in a rhythmic swinging of

the needle.

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Shoreline Effect: water and land have

different levels of conductivity causing thesignal to bend as it crosses a shoreline.(most pronounced at angles of less than

30 with the shoreline; accounted for onpublished airways.)

Terrain: mountains and natural magneticdisturbances effect signals. (accounted foron published airways.)

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Interference: if an ADF receives two

signals it will alternate back and forthbetween them until one becomesdominant. (needle will swing back and

forth.) Thunderstorms: electrical disturbances

cause static interference and erroneous orerratic indications. The needle willsometimes point towards the storm.

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ACCURACY

Systems are flight checked to an accuracy

of at least +/- 5 for approach and +/- 10for en route. The accuracy of an NDB at

any given time is difficult to determine

when considering all the factors creating

errors. However the accuracy will be

adequate for the purpose intended. (en-route 50-75nm range, approach 25nm

range.)