Non-Directional Radio Beacons: An Overview

To arrive at the right location and make a safe landing, pilots need more than a compass and good eyesight. They need navigation technologies such as differential GPS and Non-Directional Beacon (NDB) navigation. Both aviators and mariners once used NBD navigation to chart their way around the earth. Today, the former predominately use it. Below […]

Non-Directional Radio Beacons: An Overview

To arrive at the right location and make a safe landing, pilots need more than a compass and good eyesight. They need navigation technologies such as differential GPS and Non-Directional Beacon (NDB) navigation. Both aviators and mariners once used NBD navigation to chart their way around the earth. Today, the former predominately use it. Below is a brief review of how non-directional radio beacons are used to navigate aircraft, including some potential drawbacks of the technology that pilots must counteract to make it useful.

Common uses for non-directional beacons

Non-directional beacons (NDBs) are radio transmitters that are stationed at a set location, and transmit signals that serve as a navigational aid for airplanes. NDBs are distinguished from other types of transmitter technology because they do not offer inherent directional information. Rather, the Automatic Direction Finder (ADF) that is located on the plane determines the direction to the NDB location relative to the location of the aircraft. Using the ADF to trace the signals from the NDB, NBD navigation is commonly used for:

  • Determining airway paths – NBD is used to provide bearings (lines passing through the station that point in a certain direction) that define the paths that airplanes can fly.
  • Judging airway approaches – Non-directional radio beacons are frequently used as “locators” for an instrument landing system (ILS) approach or a standard landing approach. They define the starting area for an ILS approach and set a path for the standard approach.
  • “Fixing” the location of an airplane – A plane or ship can determine its location on the earth by computing a fix, which is done by extending lines through navigational reference points until they intersect.

Pros and cons of non-directional beacons

NDB navigation is preferred to other types of radio navigation technologies (e.g. VOR) because the transmitter sends signals along the curvature of the earth, which makes them readable at long distances and low attitudes. However, the technology also has potential drawbacks that do not affect competing technologies such as differential GPS, including:

  • Terrain disruption – Terrain such as mountains and cliffs can make ADFs give erroneous readings by reflecting the signal of the NDB. Terrain that contains magnetic deposits can also cause a disruption.
  • Electrical disruption – Strong electrical sources such as electrical storms or high-powered equipment may cause the needle in an ADF to veer in the direction of the electrical source and produce a false reading.
  • Shoreline disruption – If NDB signals are near a shoreline and almost parallel to it, they will refract or bend.

Pilots can compensate for these occurrences by choosing a heading that averages them out. This is far easier than trying to compensate for the disturbances during flight.

Conclusion

When they are paired with ADFs, non-direction radio beacons comprise an important navigation technology that helps pilots determine airway paths, judge airway approaches, and fix the location of an airplane. To learn more about the benefits and drawbacks of NBD technology, and how it compares to other technologies such as differential GPS, contact a provider of high-tech navigation equipment today.

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