Non-Directional Radio Beacons – Overview
To get to the right place 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. Airmen and sailors alike once used NBD navigation to chart their way around the land. Today, the former use it predominantly. Below is a brief review of how non-directional beacons are used to navigate aircraft, including some potential downsides of the technology that pilots must counter in order for it to be useful.
Common uses of non-directional beacons
Non-Directional Beacons (NDBs) are radio transmitters that are stationed at a certain location and transmit signals that serve as navigation aids for aircraft. NDBs are distinguished from other types of transmitter technology because they do not offer inherent directional information. Rather, the automatic direction finder (ADF) found on the aircraft determines the direction to the location of the NDB in relation to the location of the aircraft. Using the ADF to track NDB signals, NBD navigation is commonly used to:
- Determination of the airways – NBD is used to provide bearings (lines that pass through the station and point in a certain direction) that define the routes that aircraft can fly.
- Judging airway approaches – Nondirectional beacons are often 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 establish a path for the standard approach.
- “Fix” the location of an airplane – An aircraft or ship can determine its location on the ground by calculating a waypoint, which is done by stretching lines through navigation waypoints until they intersect.
Pros and cons of non-directional beacons
NDB navigation is preferred over other types of radionavigation technologies (eg VOR) because the transmitter sends signals along the curvature of the earth, making 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:
- Land disruption – Terrain such as mountains and cliffs can cause the ADFs to give wrong readings when reflecting the NDB signal. Soil containing magnetic deposits can also cause an outage.
- Electrical interruption – Strong electrical sources, such as electrical storms or high-power equipment, can cause the needle of an ADF to drift in the direction of the electrical source and produce a false reading.
- Shoreline disruption – If NDB signals are close to and nearly parallel to a coast, they will refract or bend.
Pilots can compensate for these events by choosing a heading that averages them. This is much easier than trying to compensate for disturbances during flight.
When combined with ADF, the directionless radio beacons comprised an important navigation technology that helps pilots determine airway routes, judge airway accesses, and fix the location of an aircraft. 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.