In air navigation, pilots make use of various forms of navigational aids en route and on approach. Two particular forms of navigational aids are VORs (Very High-Frequency Omnidirectional Radio Range) and NDBs (Non-Directional Beacons).
The major difference between the two is the high degree of accuracy of VORs when compared to NDBs. NDBs require the aircraft’s exact heading in order to function precisely, VORs do not. VORs consist of a set of dual signals, in which the differential calculates the exact course from the aircraft to the VOR.
When navigating via NDBs, there is no directional guidance available unless the aircraft is fitted with an onboard ADF or Automatic Direction Finder. In this sense, NDBs have very limited functionality.
This mode of operation makes VORs much more reliable and accurate for navigation purposes. VORs are commonly used for en-route navigation and approaches in most countries.
The vast majority of NDBs have been decommissioned for these reasons, in favor of VOR navigation.
Future of Air Navigation
Conventional navigational practices including the use of VORs are evolving in favor of RNAV (Area Navigation) and GPS (Global Positioning System) navigation. These forms of navigation allow an aircraft to perform an instrument approach into an airport that does not have physical navigational units on the ground.
These forms of approaches allow an aircraft to fly a direct approach to a runway as only two “reference” points of such are required for lateral and vertical navigation.
Although these systems do not have dedicated on-ground systems, they are commonly coupled to an existing VOR or DME ground unit as a reference point, followed by an adjustment or a shift for the selected approach path.
This form of navigation has several advantages over VORs and NDBs, most noticeably being the efficiencies associated with it. More direct approaches allow for fuel and time savings along with a smoother traffic flow at busy airports.
Advantages of VOR over NDB
When comparing VOR navigation to NDBs directly, it is apparent that there are significantly more advantages to using VORs. These advantages are the following:
- VORs offer more precision and accuracy – this is partly due to the high frequency in which VORs operate on.
- This high frequency lends itself well to adverse weather conditions – NDBs are affected by lightning and thunderstorms, VORs are not.
- The directional capability of a VOR is far greater than that of NDBs – VORs give an aircraft accurate bearings in terms of course/radial.
- While both VOR and NDB approaches are known as Non-Precision Approaches (in which no glideslope guidance is provided), VOR is by far the most accurate form.
- Greater accuracy provided by VOR approaches means the landing minimums can be lower – offering greater limitations than that of an NDB approach.
- VORs are far more common in the Western Hemisphere in the modern era than NDBs – they are prefered over NDBs due to the reasons listed above. This means there is a high degree of familiarisation amongst flight crews in regards to VOR approaches.
- When conducting an NDB approach, it is essential that pilots conduct lengthy and thorough calculations to ensure accuracy; this is a time consuming process which adds a heavy burden to the workload of the flight crew.
Disadvantages of VOR over NDB
Despite the numerous advantages stated above, VORs also have disadvantages in some instances when compared to NDBs. Some of these include:
- NDB navigation functions on the curvature of the earth, meaning that they can be utilized at lower altitudes and further distances to that of VORs which in comparison are fairly short range.
- VORs are classified as a line of sight form of navigation which means they are short range between a transmitter and a reciever; NDBs are the complete opposite of this.
- NDBs are typically inexpensive forms of navigation to install. The infrastructure required to set one up can be done at little cost when compared to VOR stations.
Types of VOR
VORs can be broken down into 3 different categories, all carry similar functions but with slight variants in regard to what their systems comprise of:
- VOR – the standard system.
- VOR-DME (Distance Measuring Equipment) – standard VOR which also consists of a DME station which provides distance in nautical miles from the reciever to the station.
- VORTAC – VOR combined with the military form; TAC (Tactical Air Navigation System). More detail regarding this form can be found here.
Aside from these 3 forms of VOR, they can also be broken down in relation to range capability, high altitude, and low altitude configurations. Detailed variants and specifications of VORs can be found on aeronautical navigational charts.