Navigation: Ground navigation equipment Flashcards
What is Loran C?
Loran C is a long-range navigation system that uses ground-based beacons that operate in the lowfrequency (LF) band using surface waves to achieve ranges of more than 100 nautical miles. It is
available in North America, the North Atlantic, Europe, and the Mediterranean.
Describe VHF directional finding (VDF).
VHF directional-finding (VDF) uses communication radio waves and does not require any additional
instrumentation in the cockpit.
It can be requested from air traffic control (ATC) at aerodromes that are equipped with radio
aerials that can sense the direction of the very high frequency (VHF) com radio signals from an
aircraft whenever the pilot transmits. This is known as automatic direction finding (DF) in the VHF
band.
This system allows ATC to provide the pilot with aural bearing information on request, either as a
QDM, QDR, QTE, or a QUJ.
Give the following Q definitions.
QUJ- True bearing TO the station
QTE- True Bearing FROM the station
QDR- Magnetic bearing(radial) FROM the station
QDM- Magnectic bearing ( radial) TO the station
Describe how an NDB/ADF system works.
A nondirectional beacon (NDB) is a medium-range radio navigational aid that sends out a signal in
all directions for aircraft to home to. The NDB transmits in the 200- to 1750-kHz medium- and lowfrequency bands and uses a surface-wave propagation path.
The automatic direction finder (ADF) is a needle indicator fitted in the aircraft that shows the
direction to the selected NDB from the aircraft. This is either displayed as a relative bearing (angle
between the aircraft heading and the direction of the NDB) on a relative bearing indicator (RBI)
instrument or as a QDM on an RMI instrument.
What is the range of an NDB?
The range of a beacon is controlled primarily by its power, with a maximum theoretical range of 300
nautical miles over land and 600 nautical miles over the sea, although its range is often restricted to
avoid interference with other signals. For example:
Land over land (NM) = 3 SRT Power output (Watts)
Land over sea (NM) = 9 SRT Power output (Watts)
What are the errors of an NDB/ADF?
The errors suffered by an NDB/ADF are as follows:
1. Interference from other NDB stations
2. Static, especially thunderstorms
3. Night effect
4. Coastal refraction
5. Mountain effect
6. Aircraft quadrantal error
7. Synchronistic transmission
The International Civil Aviation Organization (ICAO) requirement for an NDB is that it maintains
its accuracy to within ±5 degrees. However, not all errors are predictable, and therefore, it is
possible that the actual error experienced by an NDB/ADF system is greater than its designated
maximum.
What is an ADF beat frequency oscillator used for?
A beat frequency oscillator (BFO) is selected by the pilot on an automatic direction finder (ADF)
navigation box and is used when identifying any nondirectional beacons (NDBs) that use unmodulated carrier waves, i.e., NON A1A transmissions. This is needed because no audio message (Morse) can be heard by the pilot on an unmodulated carrier wave, so the BFO imposes a tone onto the carrier wave to make it audible to the pilot; thus the NDB signal can be tuned and identified. However, it
should not be left on when using the ADF to navigate.
Note: NDBs with A2A idents already modulate to an audible frequency. Therefore, the BFO is not
needed and should always be switched off.
