BRENT CROW

What is VOR Navigation?

• Very High Frequency Omni-Directional Range Radio or VOR stations provide aircraft with a “radial” to follow while flying. VOR stations send out signals to aircraft that tell them what cardinal direction they are from the station.

• Aircraft do not have to make wind corrections in order to use the station, as you would if you were using a Non-directional Beacon or NDB.

• VOR navigation is unaffected by weather, but relies on line of sight for reception.

VOR’s work by sending out two signals. The first is called the Reference phase, and its frequency stays constant. The second is its Variable phase.

Magnetic North

090 degree radial

180 degree radial

270 degree radial

VOR Station

= Reference Phase

= Variable Phase

The VOR navigation equipment in the aircrafts cockpit calculate the difference between the reference phase

and the variable phase to determine the radial the aircraft is on relative to the station.

360° phase 180° phase difference

The diagram on the left shows one full phase of the reference phase. The diagram on the right depicts what an aircraft on the 180 degree radial from the VOR would be receiving. You can see the 180 degree phase difference between the reference phase and the variable phase. Inside the

VOR station, the reference signal is broadcasted continuously with a Morse code every 10 seconds. Pilots can listen to the Morse code to determine if the station is working correctly. If no Morse code is heard, then the station is out of service. Its unclear about how the variable phase is transmitted,

but its transmitter spins at 1800 RPM.

North VOR Lighthouse ANALOGYLets pretend the VOR station is a light house. There are two things at this light house, a blue light bulb and a flashlight that spins through all compass headings. The blue light bulb is on continuously, except when the flashlight is

pointing north. The flashlight turns at a rate of one degree a second for all 360 degrees.

Now, lets say you are the pilot of the aircraft to the left. You see the blue light go off (this is the point at which the flash light is pointing north). And just as the light

turns off, you begin timing. Then you see the flashlight beam pointing directly at you 225 seconds after you started your timer. That would mean you are on the 225 degree radial (heading) from the flashlight. Its all

about timing.

A real VOR works in the same sort of manner, where the blue light is the reference phase signal, and the flashlight is the

variable phase. You can think of the heading that the flashlight is pointing is the phase difference between the reference phase

and the variable phase.

225 degrees

Omni Bearing Selector (OBS) – Spins the outer compass card so the pilot can

select the desired radial to track.

VOR Station

Magnetic North

090 degree radial

180 degree radial

270 degree radial

The black instrument on the top left of the screen is a Course Deviation Indicator. Lets say you are the aircraft depicted above, and

you tuned into the VOR station. You spun the OBS until the white CDI needle centered, telling

you that you are on the 254 degree radial FROM the station. If you wanted to fly direct to the station, then you would turn the OBS till the CDI centered with a TO flag. Then the heading at the top would indicate the heading you would need to fly in order to fly direct to the station. If you had the needle centered with a FROM flag,

the selected radial would be the heading you would fly to fly away from the station on the

current radial selected.

Selected Radial

TO/ FROM flag. Indicates whether you are going to be

traveling to or from the station if you fly the heading of the

radial selected.

Course Deviation Indicator

(CDI)

Aircraft A, B, and C all have 135 as their

selected radial in their CDI with a TO flag. Aircraft B is right on the 135

degree radial from the station, therefore the CDI is centered.

Aircraft A is to the right of the radial so the CDI is telling the

pilot that the selected radial is off

to the left of the aircraft. Aircraft C’s

CDI is telling the pilot to turn to the

right to intercept the 135 degree radial.

135

135

135

This is part of a flight I recorded to demonstrate how a VOR system is used in my everyday life. We will track the outbound 050 degree radial from Gila Bend

VOR.

INOP.

This movie has been placarded inoperative in accordance with FAR 91.213

http://www.visi.com/~mim/nav/

There is a great VOR simulator at this website. I strongly recommend you visit this website if you still have unanswered questions about the use of VOR systems.

Special Thanks to John Raatz for allowing me to record during his flight.

THE END