Aircraft navigational aids, commonly referred to as navaids and beacons, are essential tools used to guide aircraft on their routes from departure to destination safely and efficiently. These aids provide crucial information regarding the aircraft’s position relative to a desired course or location. They employ a range of technologies from conventional ground-based radio signals to precise satellite-based positioning with GPS waypoints. Let’s take a look at the different types of navigational aids and the technology behind them.
VOR (Very High Frequency Omni-Directional Range)
VOR, which stands for Very High Frequency Omni-Directional Range, is a type of navigational aid (navaid) for aircraft. Essentially, VORs are navigation systems that utilize very high frequency radio signals emitted from ground-based beacons. These stations also broadcast their three-letter identifiers in Morse code. Given that VOR signals can cover a range of approximately 200 miles, pilots often receive signals from multiple VOR stations simultaneously. Consequently, it is crucial for pilots to correctly identify a VOR station before using it for navigation to ensure they are following the correct beacon. Additionally, some VOR stations transmit a voice signal that includes the station name along with recorded advisories.
NDB (Non Directional Beacon)
A Non-Directional Beacon (NDB) is a type of radio beacon that functions in the Medium Frequency (MF) or Low Frequency (LF) bandwidths. NDBs emit a uniform signal in every direction. This signal includes a coded component, typically one to three letters in Morse Code, which serves as the station’s identifier. NDBs frequently play a role in Non-Precision Approach procedures. Aircraft are equipped with Automatic Direction Finding (ADF) equipment, which utilizes the bearings from NDB signals for navigational purposes.
DME (Distance Measuring Equipment)
Distance Measuring Equipment (DME) is a type of radio navigation system that calculates the slant range (distance) between an aircraft and a ground station. It does this by measuring the time delay of radio signals, which operate in the frequency range of 960 to 1215 megahertz (MHz). DME units are often combined with VORs or NDBs to provide additional distance information.
DME technology is also used as part of the instrument landing system. An ILS DME provides distance information to landing aircraft that are using the ILS’ localizer and glideslope, replacing the older system of individual outer, middle and inner markers.
The number of conventional navaids (such as VORs) has declined in recent years as the prevalence of GPS-based navigation has increased. In many cases, the physical infrastructure of the beacons have been replaced by digital based waypoints using the same identifiers. With the increase in global GPS interference, some VOR infrastructure is being repurposed to act as a backup navigation service that can be used in the event of GPS outages.
In addition to conventional navaids, the world is covered in tens of thousands of GPS based waypoints. These are not based on any kind of physical infrastructure, and are used for both high altitude and low altitude navigation.
Check out our GPS Jamming Map
You can view Navaids, low altitude and high altitude waypoints on Flightradar24. Head to settings, scroll down to ‘Aeronautical Charts’, and select one to add them to the map.
- Navaids refer to conventional navaids as referenced above, including VOR, VOR/DME and NDBs.
- High altitude waypoints are mostly used for operations 18,000 feet and above and appear on “Area charts.” Low altitude waypoints are mostly used for navigation from the surface to 18,000 ft. Whilst they will appear separately on low and high altitude charts, they can both appear on digital tabled based charts used in electronic flight bags.
Holding patterns and navigation aids
You may notice that some aircraft fly holding patterns around some navaids more than others. This is particularly prevalent in London, where inbound aircraft can be seen holding over the VOR DME stations at Lambourne (LAM), Bovingdon (BNN), Biggin Hill (BIG), Brookman’s Park (BPK), and Ockham (OCK).
How and why do aircraft hold at airports?
Navaids and GPS waypoints are an essential part of the global aviation infrastructure. Without them, we would not be able to guide aircraft to their destinations, fly holding patterns, oir manage and separate traffic. As the global influence of GPS interference increases, it will be interesting to observe the safeguards put in place to ensure the navigation and airways system operate safety.
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