1. VOR NAVIGATION
BRENT CROW

2. 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.

3. VOR’s work by sending out two signals
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.
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.
VOR Station
Magnetic North
270 degree radial
090 degree radial
180 degree radial
= Reference Phase
= Variable Phase

4. 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.

5. VOR Lighthouse ANALOGY
North
VOR Lighthouse ANALOGY
Lets 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.
225 degrees
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.

6. Course Deviation Indicator (CDI)
Selected Radial
Magnetic North
Course Deviation Indicator (CDI)
VOR Station
270 degree radial
090 degree radial
180 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.
Omni Bearing Selector (OBS) – Spins the outer compass card so the pilot can select the desired radial to track.
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.

7. 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

8. This movie has been placarded inoperative in accordance with FAR 91
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.

9. There is a great VOR simulator at this website
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