NON-DIRECTIONAL BEACON

1
NON-DIRECTIONAL BEACON

• NDB

2
GROUND BASED EQUIPMENT

• NDBs are rarely found in the US, But still
  common in Canada.
• Used in busier areas as a means of identifying
  approach 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.

3
AIRCRAFT EQUIPMENT

• Receiver
• Control Head
• Indicator (Automatic Direction Finder)
• Fixed Card relative bearing or 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

4
OPERATION

• The desired frequency is tuned.
• The station is identified.
• ANT setting may be used to identify station, but
  no directional information will be available, ADF
  must be selected prior to navigation.
• ADF equipment has no flag system to indicate
  reception, therefore pilots must monitor the
  audible identifier of the station anytime ADF is
  the sole means of navigation and throughout the
  approach phase of flight.
• Note some EFIS displays incorporate a flag
  warning system, making audio monitoring
  unnecessary.

5
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.

6
ERRORS

• Bank Error needle will point down to the
  station when aircraft is banked.
• Quadrantal error Caused by the refraction
  (bending) of the incoming radio waves by the
  aircraft structure.
• Minimum when station is off cardinal points
  (nose, tail, or wingtip).
• Maximum in between.

7
LIMITATIONS

• Skip Zone an area of erratic indication or
  signal loss 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 sunrise and
  sunset. Has a greater effect on higher
  frequencies. More pronounced further from the
  station.
• Fading similar to night effect although the
  erratic indications are caused by out of phase
  signals.

8

• Shoreline Effect water and land have different
  levels of conductivity causing the signal to bend
  as it crosses a shoreline. (most pronounced at
  angles of less than 30 with the shoreline
  accounted for on published airways.)
• Terrain mountains and natural magnetic
  disturbances effect signals. (accounted for on
  published airways.)

9

• Interference if an ADF receives two signals it
  will alternate back and forth between them until
  one becomes dominant. (needle will swing back and
  forth.)
• Thunderstorms electrical disturbances cause
  static interference and erroneous or erratic
  indications. The needle will sometimes point
  towards the storm.

10
ACCURACY

• Systems are flight checked to an accuracy of at
  least /- 5 for approach and /- 10 for 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.)