VOR stands for VHF Omnidirectional Range. It's a ground-based radio navigation aid that tells an aircraft its bearing to or from a fixed station, and it has quietly underpinned civil aviation navigation since the 1940s. This guide covers the physics behind it, the cockpit instruments that display it, and the actual flying skill of intercepting, tracking, and cross-fixing with it.
Strip away the acronym and a VOR does one job: it lets an airplane, anywhere within range and line of sight, determine which of 360 possible directions it lies from the station. No distance, no altitude, just a bearing, accurate to about a degree. Combine that bearing with a second one from another station, or with a distance from a co-located DME, and you have an actual position. Combine a whole chain of VORs and you have the backbone of the airway system that has guided airliners, cargo flights, and student pilots for eighty years.
Before VOR, the standard en-route aid was the four-course radio range, which broadcast Morse-coded tones that overlapped into a steady note along exactly four fixed courses, and nothing usable in between. VOR, standardized after World War II and built out through the 1950s and 60s, replaced that with continuously variable bearing information across all 360 courses, to a precision of about a degree. It became the foundation of the Victor airway system that still appears on charts today.
GPS has taken over as the primary means of en-route and approach navigation for most operators, but VOR hasn't gone away, for a few concrete reasons: it's a non-satellite backup (the FAA maintains a deliberately thinned-out Minimum Operational Network, or MON, so aircraft can still navigate if GPS is degraded), it's still charted and flyable (Victor airways, VOR approaches, and VOR-defined holds are all still active), and it's still required knowledge on every private and instrument checkride, both because it's operationally relevant and because understanding phase-comparison navigation builds real navigational judgment.
A VOR ground station broadcasts two signals on the same VHF carrier frequency and compares them. The difference between them is the bearing. A reference phase signal, 30 Hz, is broadcast identically in every direction. A variable phase signal, also 30 Hz, is produced by an antenna pattern that effectively sweeps around the station 30 times per second. The two signals are exactly in phase at magnetic north (the 360° radial); moving clockwise, the variable signal's phase lag increases in lockstep with the angle, 90° of lag at the 090 radial, 180° at the 180 radial, and so on. An aircraft's receiver measures that phase difference and reports it directly as the radial.
A conventional VOR (CVOR) produces the rotating signal with a directional antenna pattern that mechanically or electrically rotates, which makes it sensitive to siting: nearby terrain or buildings can reflect the signal and distort it. A Doppler VOR (DVOR) instead uses a ring of fixed antennas switched on in rapid sequence, electronically simulating rotation, which is considerably more resistant to siting errors. From the cockpit, a DVOR and a CVOR behave identically; the difference is purely in how the ground station generates the signal.
Not every VOR symbol on a chart represents the same equipment.
| Facility | Provides | Notes |
|---|---|---|
| VOR | Bearing only | The baseline facility. No distance information. |
| VOR/DME | Bearing + distance | A VOR co-located with Distance Measuring Equipment, giving a fix from a single station. |
| VORTAC | Bearing + distance | A VOR co-located with a military TACAN; civil aircraft use the VOR bearing and the TACAN's DME-equivalent distance. |
| TVOR | Bearing only, shorter range | Lower-powered, terminal-area use. Typically reliable to roughly 25 nautical miles. |
| VOT | A single simulated radial | Not a navigation aid, a ground facility used only to check receiver accuracy. |
Most VORs charted along major airways today are VOR/DME or VORTAC facilities, since a single station then gives a real position fix without needing to cross-reference a second VOR.
A radial is a magnetic bearing measured from the VOR station, outward. Every VOR broadcasts 360 of them, one in every direction, like spokes on a wheel. Radials are always numbered from the station, outward, never toward it. If you're on the line labeled 045°, you're "on the 045 radial," regardless of which direction your nose is pointed. Flying outbound on it, you'd fly roughly 045°; flying inbound toward the station along that same line, you'd fly the reciprocal, roughly 225°, described as "inbound on the 045 radial." The radial names the line, not your direction on it.
The station broadcasts a bearing. The cockpit turns that into something you can act on, with three parts working together.
The VOR receiver is tuned to the station's frequency (108.00–117.95 MHz), demodulates the reference and variable signals, and computes the radial. The OBS (Omni Bearing Selector) is the rotatable knob that lets you select a desired course; turning it doesn't change the signal, only what the instrument compares your position against. The CDI (Course Deviation Indicator) is the needle that swings left or right of center to show how far off the selected course you are — on a standard receiver, each dot typically represents about 2° of deviation, full-scale roughly 10–12°. A small TO/FROM indicator shows whether flying the selected course would take you toward the station or away from it; misreading this flag is the single biggest source of reverse sensing. An OFF flag means the signal is too weak or unreliable to trust.
Four things, read together, tell you everything the instrument knows: the selected course, the needle's deflection, the TO/FROM flag, and whether your heading makes the first three meaningful.
The basic procedure: (1) tune and positively identify the station, never skip this; (2) rotate the OBS until the needle centers, or dial in the course you intend to fly; (3) read the TO/FROM flag; (4) read the needle's deflection to see how far off course you are.
The CDI's left/right logic only works intuitively when your heading roughly agrees with the selected course. If you fly a heading closer to the course's reciprocal, the needle still deflects correctly by the underlying geometry, but it stops matching your instinct for which way to turn. This is reverse sensing, and it's disorienting because the instrument still looks normal.
Getting established on a desired radial, and staying there despite wind, comes down to two techniques.
Intercepting: a shallow intercept (20–30°) closes gradually; a steep one (60–90°) gets you established quickly but needs a more decisive turn. A 30–45° intercept is a comfortable default. Watch the needle move toward center, and time your turn onto course so you arrive wings-level right as it centers.
Holding the radial: wind will push you off course again once established. That drift is wind, not error, and the fix is a wind correction angle (WCA) — a small heading adjustment into the wind. Find it by bracketing: apply a small correction (5° is a common start), watch the needle over a minute or two, then refine. If it still drifts the same way, add more; if it now drifts the other way, split the difference.
Fly directly over, or nearly over, a VOR station, and your instruments will briefly go strange: the needle wanders, the TO/FROM flag flickers, sometimes flags OFF entirely. A VOR's vertical coverage pattern is weak almost directly overhead, like an inverted cone standing on the station, where the phase comparison the receiver depends on breaks down. This is normal and expected, and pilots use it deliberately as confirmation of station passage. The size of the cone scales with altitude: wider, and the wandering lasts longer, the higher you fly over the station.
A single radial only tells you that you're somewhere along one line. Tune a second VOR, center its CDI, and note that radial too, a second line from a different station — your position is wherever the two lines cross. What matters is the angle of cut: a cut close to 90° gives a sharp, well-defined intersection, while a shallow cut makes it mushy and sensitive to small reading errors. Look for stations whose radials differ by 30–150°, with something close to 90° ideal. A single VOR/DME or VORTAC gives you a fix on its own, since the DME distance functions as the "second line," a circle of constant distance intersecting the one radial at a single point.
A Victor airway is a defined route built along a specific radial (or sequence of radials) connecting one VOR to the next, generally below 18,000 feet, labeled "V" followed by a number (V23, V495). Flying one is just radial tracking strung end to end: fly outbound on the defined radial, then transition to the next station, usually at a crossing radial, a DME distance, or station passage.
Every VOR-type facility is drawn inside the same circular compass rose; what changes is the symbol at the center: a plain VOR is a hexagon alone, a VOR/DME is a hexagon inside a square, and a VORTAC is a hexagon with three tabs on alternating sides. A TVOR uses the same plain hexagon as a standard VOR, with a smaller or truncated compass rose reflecting its shorter range.
A frequency alone doesn't guarantee you're receiving the station you think you are. Every operating VOR continuously transmits a unique three-letter Morse identifier, often alongside a synthesized voice ID, printed on the chart both as letters and as its Morse pattern. When a VOR is out of service, its identifier is either removed or replaced with a maintenance code.
14 CFR 91.171 requires pilots operating under IFR to check their VOR receiver within the preceding 30 days. Four approved methods: a VOT (tolerance ±4°), a certified ground checkpoint (±4°), an airborne checkpoint (±6°, looser since it's harder to hold position precisely in the air), or a dual VOR cross-check comparing two receivers against each other (must agree within ±4°). Results must be logged for aircraft used in IFR operations.
VOR operates in the VHF band, so signals travel in a straight line and don't reliably bend around terrain or the earth's curvature. As a rough rule of thumb, VHF line-of-sight range in nautical miles is approximately 1.23 times the square root of altitude in feet above the station: roughly 87 nm at 5,000 feet, roughly 174 nm at 20,000 feet. Mountains, ridgelines, and large buildings can reflect the signal, producing small, sometimes-fluctuating bearing errors called scalloping, which Doppler VOR was specifically designed to reduce.
| Source | Typical effect |
|---|---|
| Line-of-sight range | No signal at all beyond the radio horizon for your altitude |
| Terrain / reflection ("scalloping") | Small, sometimes fluctuating bearing errors near affected sites |
| Cone of confusion | Temporary, expected instability directly over the station |
| Station and receiver tolerance | A few degrees of routine bearing error under normal conditions |
| Interference | Erratic or unreliable indications, sometimes an OFF flag |
You depart south of FLI VOR, planning to track outbound on the 058° radial toward your destination. Tune and identify FLI before takeoff, confirming the Morse identifier. Set the course to 058° on the OBS; since you're departing south and flying away from the station, confirm the flag reads FROM. Intercept: the CDI shows you slightly east, so you turn to 030° and watch the needle walk toward center. Establish on course by rolling out on 058° as the needle nears center. Hold the radial: a crosswind pushes you south, so you apply a 6° correction (flying 052°) and the needle holds steady. Cross-check with a second VOR partway along the leg to confirm you're on track. Nothing in this walkthrough is a special technique, it's Chapters 5 through 9, applied in sequence.
The full PDF includes all diagrams and 17 practice questions with a worked answer key.
This guide is intended for educational and training purposes only. It is not a substitute for official FAA publications, an authorized ground school, or qualified flight instruction, and should not be used as a sole source for real-world flight planning, dispatch, or operational decisions.