VOR is a short-range radio navigation system and the most common ground-based NAVAID. It operates in the 108.0 MHz-117.95 MHz band, continuously broadcasting a stationary master signal together with a rotating variable signal. The airborne receiver compares the phases of the two signals and instantly presents a magnetic bearing from the station.
Because VOR provides magnetic bearings, pilots can use it to fly point-to-point along published airways that hop from one VOR beacon to the next. Effective coverage is divided into three overlapping service volumes: at its high-altitude tier the signal can be relied on out to 40 nautical miles from 1,000 ft above the station to 14,500 ft, out to 130 nautical miles from 18,000 ft to 45,000 ft, and out to 100 nautical miles from 45,000 ft to 60,000 ft.
Although VOR gives only directional guidance and thus supports non-precision approaches without vertical cues, variants like VOR-DME couple distance-measuring equipment to supply both bearing and slant-range, while test facilities (VOT) and those stripped of voice capability (VORW) allow for routine calibration and silent service respectively. Understanding this omnidirectional beacon's range bands and guidance types clarifies why, despite satellite systems, VOR remains a backbone of en-route and terminal navigation worldwide.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is VOR in aviation?
VOR stands for very high frequency omni-directional range, which is short-range radio navigation that pilots use for navigation. VOR-DME combines VHF omnidirectional range with distance-measuring equipment, and aircraft can pick up signals from multiple VOR stations.
At the ground station, radio beacons emit very high frequency radio waves that are received by aircraft. Each VOR station broadcasts a three-letter identifier in Morse code, and this identifier is also voiced. The identification is always followed by ‘VOR’ after the range's name.
The composite signal emitted by the station is a line of position called a VOR radial, and the magnetic bearing the aircraft observes corresponds exactly to that radial. An omnibearing selector in the cockpit allows the pilot to choose one of the 360 possible radials. When the CDI is centered it indicates the aircraft is on the selected radial, and the sense indicator shows ‘From’ when the CDI is centred on a radial radiating from the station. Signal range is approximately 200 miles (321.87 km), giving continuous position guidance far beyond the immediate vicinity of the airport.
VOR infrastructure constitutes the foundation of en-route navigation. Its central rule employs phase-compare techniques to decide the magnetic radial from a ground facility. By adjusting frequency the pilot identifies the chosen station and interprets the continuous track-variation sign. Functional continuity makes the signal uninterrupted even when satellite data is corrupt, so the technology persists to function as a reliable substitute.
What is the primary function of VOR in aircraft navigation?
The primary function of Very High Frequency Omnidirectional Range (VOR) in aircraft navigation is to provide a bearing from the station to the aircraft that does not vary with wind or aircraft orientation. The aircraft's VOR receiver compares the difference between the variable and reference phase of the transmitted signals and thereby determines the aircraft's bearing from the station. This bearing is the radial the aircraft is currently on and is expressed as azimuth information in magnetic heading.
Equipped with continuous knowledge of which radial they are flying, pilots can fly point-to-point along established airways between VORs, turning from one published radial to another at common checkpoints. In this way VOR provides radials that form the skeleton of en-route procedures and departure procedures, and enables pilots to confirm position by picking up multiple VOR signals.
The real significance of the VOR instrument rests in its capacity to give both lateral direction and location data. It gives for precise en-route guidance yet without visual signs. By choosing a particular radial on the VOR, I can identify whether I am on the 090-degree radial or the 180-degree radial, and I can locate my precise whereabouts along that path.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
What is the frequency range for aircraft VOR?
The frequency range for aircraft VOR is 108.0 MHz to 117.95 MHz. All VORs operate within this very high frequency band, using channels spaced 50 kHz or 100 kHz. The first 4 MHz, from 108.0 MHz to 112.0 MHz, is shared with the instrument landing system band. Terminal VOR stations use this lower segment, while en-route VORs use 112.0 MHz to 117.95 MHz.
What are operational issues of VOR in aviation?
Operational issues include that VOR signals are blocked by terrain and obstacles. Trees located outside FAA-controlled areas cause interference. Obstacle encroachment causes signal restrictions. Signal restrictions impact en-route, arrival, and departure procedures.
VOR stations are costly and have range limitations. Big and robust VORs were expensive to maintain, and VOR stations require maintenance. The need for maintaining the current network of VORs is diminishing, and the FAA is gradually reducing the number of VORs. The FAA plans to maintain a VOR Minimum Operational Network (MON), which will assure redundancy and assure that at least one airport will be within 100 Nautical Miles. The FAA altered the Standard Service Volumes in December 2020.
What is the difference between VOR and DME in aviation?
The differences between VOR and DME in aviation are given in the table below.
| VOR | DME |
|---|---|
| VHF omnidirectional range | Distance-measuring equipment |
| Provides course information | Provides slant range distance |
| No specific range measurement | Measures time-lapse of signal transmitted by aircraft to station and responds back |
| Does not provide distance | Provides pilots an indication of the aircraft's distance from the VOR station |
| Operates on VHF band | Operates on UHF (L-band) |
| Transmits coded ident | Transmits the same coded ident as the VOR, but sends it during the pause between successive VOR idents |
| No requirement for line-of-sight | Requires line-of-sight between the aircraft and the ground station |
| No specific height dependency | Slant range is dependent on the height of the aircraft |
| Used for non-precision approaches | Facilitates separation and control of aircraft in non-radar airspace based upon VOR/DME fix reported by aircraft |
| No specific speed or time-to-station readouts | Can provide groundspeed and time-to-station readouts by differentiation |
| Not typically used for holding patterns | Permits more accurate flying of holding patterns and DME arcs |
| Does not integrate with other systems for RNAV | Basis for simple Area Navigation (RNAV) system when appropriate computerization is fitted |
| No specific frequency pairing | 200 DME channels are paired with 200 VOR/LOC channels |
| No specific frequency selection | DME frequency is automatically selected when VOR frequency is tuned |
| No specific terrain or horizon dependency | Terrain and distance beyond the horizon will prevent DME from working |
The difference between VOR and DME in aviation is that VOR gives only bearing, telling the pilot which radial the aircraft is on, but not how far along that radial it lies. DME, a short-/medium-range secondary-radar system, fills the gap by providing continuous slant-range distance in nautical miles, a circular position line centered on the ground station.
When the two aids are co-located the installation is called a VOR/DME. The airborne set tunes a single frequency: the VHF VOR is received directly, while the paired UHF DME channel is automatically selected. The DME transponder replies to each aircraft interrogation, and the airborne timer converts the round-trip delay into distance, groundspeed and time-to-station.
Because the DME measures slant range, the reading increases with aircraft height. The value displayed is the straight-line distance from the antenna to the receiver, not the horizontal miles shown on the chart. This slant-range effect is accepted by procedure designers and is used by pilots to cross-check altitude and to identify the exact point at which to start a continuous descent final approach (CDFA).
I understand that the basic distinction consists in the navigational information each instrument gives. VOR is mainly involved with heading; it provides a radial, which is a magnetic heading from the facility, and tells me where I am in comparison to that fixed location on the compass. DME is solely involved with distance; it offers an immediate output of my slant-range length to the facility in nautical miles and answers the question of closeness. When a VOR facility is connected with a co-located DME, the coupling produces a strong integration known as VOR/DME. This coupling gives both radial and distance, giving me an exact geographical location and letting me identify my precise location.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
What are the types of VOR navigational stations aviation?
VOR navigational stations include three basic configurations: VOR, VOR-DME, and VORTAC. Inside each configuration, the FAA classifies the stations into three service-volume categories: Terminal (T), Low (L), and High (H). Terminal VOR is typically located near airports, covers 25 NM (46.3 km), and serves traffic from the surface up to 12,000 ft (3,658 m). Low-altitude VOR extends the signal from 1,000 ft (305 m) to 18,000 ft (5,486 m) out to 40 NM (74.1 km), whereas high-altitude VOR projects radials from 1,000 ft (305 m) to 60,000 ft (18,288 m) and reaches 130 NM (240.7 km).
In 2022 the FAA introduced two new service-volume types - VOR Low (VL) and VOR High (VH) - to replace the legacy L and H classes. VL covers radials out to 40 NM (74.08 km) from 1,000 ft (304.8 m) to 5,000 ft (1,524 m) above transmitter height, whereas VH extends 40 NM (74.08 km) to 130 NM (240.76 km) from 1,000 ft (304.8 m) to 60,000 ft (18,288 m). A VORTAC combines a VOR with Tactical Air Navigation (TACAN) and carries any of the T, L, H, VL, or VH designators. It provides both TACAN azimuth and TACAN distance as well as the standard VOR bearing. Whatever the class, every VOR must be flight-checked through one of four approved VOR check types: VOT check, ground checkpoint check, airborne checkpoint check, or dual-VOR check.
