VOR operation & limits

The VOR is older, dumber, and more honest than GPS. It tells you exactly one thing — your angle from a ground station — and it tells you the same way it did in 1955. Learning it teaches you what "course" actually means.

How a VOR works

A VHF Omnidirectional Range station transmits on 108.0–117.95 MHz and effectively paints 360 radials outward, one per degree, referenced to magnetic north. Think of it as 360 spokes you can ride toward or away from the hub.

It's line-of-sight: usable range grows with altitude and is blocked by terrain. Down low behind a ridge, the signal simply isn't there. And a VOR tells you only which radial you're on — your bearing from the station. It says nothing about distance (that takes DME) or which way your nose is pointed.

Reading it: OBS, CDI, and TO/FROM

• The OBS (Omni-Bearing Selector) is how you ask the question: dial a course, and the instrument tells you where you are relative to it.
• The CDI (Course Deviation Indicator) needle shows how far left or right of that selected course you are. Center the needle and you're on the course; a typical CDI shows full-scale deflection at about 10° off course.
• The TO/FROM flag resolves an ambiguity: the same line through the station is one radial going TO and its reciprocal going FROM.

A quick orientation trick: center the needle with a TO flag and read the OBS — that's the magnetic course to the station. Center it with a FROM flag and the OBS reading is the radial you're on. If you set 360 and the needle sits left with a FROM flag, you're east of the 360 radial and the course back to the line is to your left.

Reverse sensing is a CDI-interpretation trap. Set a course roughly 180° opposed to the way you're actually flying and the needle works backward — fly toward it and you steer away from course. The cure is to set the OBS to roughly your intended course, and it reads normally. (On an HSI, the course needle rotates with your heading, which eliminates reverse sensing entirely — but the underlying radial logic is identical.)

Don't confuse reverse sensing with the cone of confusion. The cone is a physical signal phenomenon, not an interpretation error: directly over the station the signal is briefly unusable, so the flag flickers and the needle swings as you pass through. It's how you know you crossed the station — covered as station passage in S2.

The trainer below is all of that made touchable — drag the airplane around the station, spin the OBS, and watch the needle, the flag, and (with the reveal on) the radial math agree with each other.

Service volumes and identifying the station

VORs come in standard service volumes — Terminal, Low, and High — that define the usable range and altitude band (the FAA's VOR MON program is adding expanded VL/VH volumes as it thins the network into a backup system).

Always confirm the Morse code identifier before you trust a VOR. A station down for maintenance may still radiate an unreliable signal but remove its ident — so no ident means no navigation, full stop.

Limitations and accuracy checks

A VOR gives bearing only; pair it with DME (or use a VOR/DME or VORTAC station) and you also get slant-range distance, which turns a single station into a position fix. Beyond its line-of-sight range, a VOR can read slightly off — which is why accuracy checks exist (a VOT, a designated ground or airborne checkpoint, or a dual-VOR comparison) before a VOR is used for IFR. For VFR cross-country you aren't required to run them, but it's worth knowing the system is checked, not simply assumed.