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    Ground-Based Navigation (Week 9)

    Uploaded by

    Shane Vince
    Ground-based navigation systems like NDBs and VORs allow pilots to navigate precisely to any point. NDBs transmit a continuous three-letter identification in code. NDBs operate in low or medium frequencies, transmitting in all directions. An ADF installed in an aircraft uses two antennas to indicate the direction of an NDB. ADFs can have fixed or movable cards to display the bearing to the NDB. While NDBs do not require line-of-sight, their signals can be affected by terrain, weather, electrical interference and other factors, limiting their accuracy for navigation.

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    Ground-Based Navigation (Week 9)

    Uploaded by

    Shane Vince
    161 views17 pages
    Ground-based navigation systems like NDBs and VORs allow pilots to navigate precisely to any point. NDBs transmit a continuous three-letter identification in code. NDBs operate in low or medium frequencies, transmitting in all directions. An ADF installed in an aircraft uses two antennas to indicate the direction of an NDB. ADFs can have fixed or movable cards to display the bearing to the NDB. While NDBs do not require line-of-sight, their signals can be affected by terrain, weather, electrical interference and other factors, limiting their accuracy for navigation.

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    Ground-based navigation (Week 9)

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    Ground-based navigation systems like NDBs and VORs allow pilots to navigate precisely to any point. NDBs transmit a continuous three-letter identification in code. NDBs operate in low or medium frequencies, transmitting in all directions. An ADF installed in an aircraft uses two antennas to indicate the direction of an NDB. ADFs can have fixed or movable cards to display the bearing to the NDB. While NDBs do not require line-of-sight, their signals can be affected by terrain, weather, electrical interference and other factors, limiting their accuracy for navigation.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    161 views17 pages

    Ground-Based Navigation (Week 9)

    Uploaded by

    Shane Vince
    Ground-based navigation systems like NDBs and VORs allow pilots to navigate precisely to any point. NDBs transmit a continuous three-letter identification in code. NDBs operate in low or medium frequencies, transmitting in all directions. An ADF installed in an aircraft uses two antennas to indicate the direction of an NDB. ADFs can have fixed or movable cards to display the bearing to the NDB. While NDBs do not require line-of-sight, their signals can be affected by terrain, weather, electrical interference and other factors, limiting their accuracy for navigation.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
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    Ground-based Navigation

    ATRN 214
    Ground-based navigation

    Advances in navigational radio receivers installed in aircraft, the development of aeronautical


    charts that show the exact location of ground transmitting stations and their frequencies,
    along with refined flight deck instrumentation make it possible for pilots to navigate with
    precision to almost any point desired.

    All radio beacons, except compass locators, transmit a continuous three-letter


    identification in code, except during voice transmissions. A compass locator, which is
    associated with an instrument landing system, transmits a two-letter identification.
    Radio navigation systems available for VFR navigation

    • Nondirectional Radio Beacon (NDB)


    • VHF Omnidirectional Range (VOR)
    • Global Positioning System (GPS)
    Nondirectional Beacon and
    Automatic Direction Finder
    Nondirectional Beacon (NDB)

    • Is the simplest NAVAID used by aircraft.


    • It is a ground-based transmitter which transmits radio energy in all directions, hence its
    name – the nondirectional beacon
    • The NDB stations normally operate in a low or medium frequency band
    • The radio frequencies assigned to NDBs shall be selected from those available in that portion of the
    spectrum between 190 kHz and 1750 kHz (based on ICAO Annex 10 Vol 1 3-34)
    • The NDB frequency can sometimes bleed over to the AM Radio frequency band and likewise
    radios can bleed over onto the NDB frequency
    NDB in Charts
    NDB Range

    • The range of NDB depends on:


    • The power of transmission (10-2000 watts)
    • The frequency of transmission
    • Atmospheric conditions at the time
    • The nature of the earth’s surface over which the signal travels
    Automatic Direction Finder (ADF)

    • Installed in an airplane, has a needle that


    indicates the direction from which the
    signals of the selected NDB ground station
    are being received.
    • In the past days, the ADF was referred to
    as radio compass
    ADF Antennas

    An ADF requires two antennas.

    1. Directional antenna
    • is a flat device about the size of your hand, containing loops of wire that receive radio signals more
    efficiently in one direction than in others.
    2. Sense antenna
    • receives signals with equal efficiency in all directions.
    The ADF will point to the
    NDB it is tuned to.
    Bearing

    A bearing is the horizontal direction from one point to another. It can be measured
    clockwise in degrees from any reference point.

    • Relative bearing (RB) - is the clockwise angle from the heading of the vessel to a straight
    line drawn from the observation station on the vessel to the object.
    • Magnetic bearing (MB) - refers to the angle between the magnetic north and an object.
    • True bearing (TB) - refers to the angle between the true north and an object.

    Relative Bearing + Magnetic Heading = Magnetic Bearing


    ADF Bearing Indicators

    • Fixed-card bearing indicator


    • the number zero always appears at the top, and the numbers around the 360° azimuth card
    correspond to a station’s bearing relative to the nose of the airplane (relative bearing).
    • Movable-card bearing indicator
    • Pilot can rotate the face of the card.
    • The ADF needle will directly indicate the magnetic bearing to the NDB when the aircraft heading is
    shown at the top.
    • Radio Magnetic Indicator (RMI)
    • Is similar to the movable-card indicator except that it automatically adjusts itself to the present
    aircraft heading.
    A view of fixed-
    card bearing
    indicator
    A view of movable-
    card bearing
    indicator
    Advantages of NDB/ADF

    • Low or medium frequencies are not affected by line-of-sight. The signals follow the
    curvature of the Earth; therefore, if the aircraft is within the range of the station, the
    signals can be received regardless of altitude.
    • Accuracy is suitable for navigation but subject to numerous limitations
    • Relatively simple and low cost
    Limitations

    • Radio beacons are subject to disturbances that may result in erroneous bearing
    information. Such disturbances result from factors such as lightning, precipitation static,
    etc.
    • Nearly all disturbances which affect the Automatic Direction Finder (ADF) bearing also
    affect the facility's identification
    • Noisy identification usually occurs when the ADF needle is erratic
    • Voice, music or erroneous identification may be heard when a steady false bearing is being
    displayed
    • Since ADF receivers do not have a "flag" to warn the pilot when erroneous bearing
    information is being displayed, the pilot should continuously monitor the NDB's
    identification
    Limitations
    • Twilight Error (Night Effect)
    • Radio waves can be reflected back by the ionosphere and can cause fluctuations 30 to 60 NM
    (approx. 54 to 108 KM) from the transmitter, especially just before sunrise and just after sunset
    • Terrain Error:
    • High terrain like hills and mountains can reflect radio waves, giving erroneous readings especially if
    they contain magnetic deposits
    • Electrical Error:
    • Electrical storms, and sometimes also electrical interference can cause the ADF needle to deflect
    toward the electrical source
    • Shoreline Error
    • Low-frequency radio waves will refract or bend near a shoreline, especially if they are close to parallel
    to the shore
    • Bank Error
    • When the aircraft is banked, the needle reading will be offset

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