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Another Podcast – The VOR

VOR stands for Very High Frequency Omni-Directional Radio Range. Why do we care? Like always, because we have an intense interest in how airplanes work, and the VOR is a great navigation aid. We also care because there will be a couple VOR questions on the test and they’ll be easy to get if you understand how the VOR works.

So, a VOR is a very high frequency omni-directional radio. What’s it look like? You may have seen one. You find them at some airports. There’s one at CYPK, where I normally fly out of, for example. They have a center cone/antenna surrounded by a big ring, and when I say “big” I mean that the diameter of a VOR could easily be 25 feet. Once you’ve seen one you’ll pick them out easily, and they’re easy to see from the air.

They work by sending out two VHF radio signals in a range between 108 and 117.95 mhz. The signals from a particular VOR are sent out all on the same frequency. One is a master signal, and the second is a directional second signal. The difference in direction between each of the two signals can be measured, and once measured can be assigned a direction in degrees. That means that a VOR can send out a signal on each degree of the compass and a VOR receiver in the aircraft can receive that signal and indicate exactly when the airplane is in line with it.

You can see how the VOR in your plane could tell you exactly what direction you are from the VOR on the ground at a particular airport. You wouldn’t know how far away you are, but you’d know exactly what direction you were from the airport because you’d be on the line that corresponds with one of the secondary signals.

These lines are called “radials”, and are always described as coming from the airport’s VOR. There is a radial for every direction, and the radials originate at the station. This concept of “from” is important. Be clear that a 090 radial is a line traveling due east from the station. If your airplane is on that line you could be flying west to the station, east from the station or just crossing that line going in any random direction. The radial is just a line coming from the station.

That means that radials from the VOR are exactly opposite what you fly to the station. If you’re on the 090 radial from the station you’d fly 270 to the station. If you arrived at the station and overflew it, continuing on the same heading, you’d change from being on the 90 degree radial from the station to being on its reciprocal, the 270 degree radial from the station.

Radials from the VOR are what you fly outbound on your way to another VOR or some other destination.

You can see the simple application. Assuming there are no obstacles like mountains in the way you can follow a radial from your VOR equipped airport to your destination, or at least very close to it.

You can also follow a radial from your starting point, and then somewhere along the route begin following a radial to a second VOR if your destination airport is VOR equipped.

The concept of two different VORs also allows for the idea that you can pin point your location by finding the intersection of two VOR radials from two different VORs. You get onto one radial and fly along it, either to or from. Take into account what the wind is doing and adjust your heading so that you fly a track that keeps you on the radial (heading, remember, is the compass heading you steer, and track is what you actually fly). Then, once you’re confident you’re flying on the first radial, dial in the second VOR and look for a radial from that station. The two radials from different VORs can only intersect in one place.

The idea of “from” and “to” can be confusing, so one thing to remember is “from top / to bottom”, meaning you read the “from” direction at the top of the VOR gauge and the “to” direction at the bottom. The “from” and “to” flags indicate what side of the station you are on, relative to the radial you’ve dialed in. If you’re within 90 degrees of the radial (either way) you’ll see a “from” flag. Let’s use the 30 degree radial as an example. The 30 degree radial starts at the station. If you’re anywhere within the 180 degree semi-circle starting at 300 degrees and going through 30 degrees to 120 degrees and you’ve got the 30 degree radial set at the top of the VOR, the flag will read “from”. You’re on the same side of the station as the 30 degree radial.

If you’re on the opposite side of the station as the 30 degree radial, that is, somewhere between 120 degrees and 300 degrees, for example, 270 degrees, the flag will read “to”.

In other words, if you’re looking for the 30 degree radial from the particular airport (or station) you line up 30 degrees on the VOR compass card at the top. When you center the needle the pointer will read “from” if you’re on the same side of the VOR station as the radial. You’ll see that the needle is centered, that the pointer is “from” (pointing down) and you’ll know that you are on the radial that departs the station VOR on the 30 degree radial. If the VOR reads “to” with 30 degrees centered at the top of the VOR face and the needle is centered, you know you’re on the reciprocal radial to 30, which is the 210 degree radial from the station.

Another way to look at it is that if you look at the bottom of the VOR you’ll see the reciprocal of 30 degrees (210 degrees). Its at the bottom. From top. To bottom. If you want to fly to the station you fly the heading at the bottom, or 210 degrees. In practice you dial the VOR around until 210 is at the top, and the marker will switch from “from” to “to”. In other words, find the radial that you’re on with the “from” flag showing, then set reciprocal hdg on top and if you’ve done it right the needle will be centered and say “to”. You can then fly to the VOR (obviously correcting for drift – your heading may be different in order to maintain the track).

What’s it mean when the needle is not centered? Simple. It means the radial you’re looking for is on the same side of the aircraft as the needle is. Steer that way and the needle will eventually go live and then go to the center. Just look at what side the needle is on and steer that way to center the needle.

On the test there will probably be questions that show the face of a VOR, or possibly an airplane and a radial and multiple VOR faces. You’ll need to be able to figure out either what the single VOR is telling you or which one of multiple VOR pictures accurately represents the position of the airplane and radial.

Remember first that radials are always from the station. Remember second “From bottom/to top”, and remember third that the needle will be on the side of the VOR that the radial is on relative to the airplane.

Also remember that before you can get to “from” you need to get “to” the VOR. In other words, using our 30 degree radial example again, if you have the 30 degree radial dialed in at the top of the compass card, and the needle is centered, but the flag says “to”, you are between 120 degrees and 300 degrees, or southwest of the VOR in question. You’re actually on the 210 radial from the VOR and flying a 30 degree heading (ignoring wind and drift for the moment) to the VOR along the 210 radial.

For example, if you see a diagram of an airplane on the same side of the station as a radial that’s drawn in of 300 degrees you’ll know that the radial is from the station, and so 300 should be at the top (from “top”) with the flag indicating “from”. If the reciprocal of 300 degrees (120 degrees) is at the top of the VOR compass card then the flag should read “to”. Remember, you have to get “to” the VOR before you can be “from” the VOR. Remember: figure out where the airplane in the diagram is in relation to the VOR radial. If it’s within 90 degrees either way of the radial in the drawing then you’re on the same side of the VOR station as the radial, and the flag should read “from”. If you’re more than 90 degrees away from the radial (and remember, we’re referring to a diagram), then the flag should read “to”.

They may also give you questions where you can choose between various VOR gauge faces, with the question asking which combination of faces best represents the track a plane is flying. Again, you’ll see a diagram. They’ll try to confuse you by changing the VOR compass card, and the diagram will show two airplanes with each one on opposite sides of a VOR radial (let’s use the 30 degree from radial). The question will ask which combo of VOR faces represents the diagram accurately. One face may read 30 at the top, with a “from” flag, and the needle on the correct side (the airplane would be at 50 degrees off the VOR, so the needle would be on the left hand side). That’s fine. Once the airplane crosses the 30 degree radial it could still be “From”, but the needle should switch to the right side of the gauge. However, if you dialed the compass card to the reciprocal heading (210) the needle would stay on the same side, but the flag would change to “to”. Remember, the 30 degree radial from is the same as the 210 radial “to”. Its a way to trick you. Rather than flip the needle they flip the flag.

Another trick is to put the drawing of the airplane on the opposite side of the radial (i.e., more than 90 degrees away from the “from” radial), meaning you are on the “to” side of that radial. We’ll use 30 degrees again. Say the radial is drawn in at 30 degrees and the airplane is drawn in at 230 degrees. You’d think the VOR would read 30 degrees at the top, with the flag saying “to”, and the needle on the
VOR being to the right. However, they can trick you by putting the reciprocal heading at the top, meaning the flag will say “from” and the needle will be on the opposite side, that is, the left.

An easy way to solve this problem and avoid confusion on the test is to draw the reciprocal radial in. Using the example above we’d draw in the reciprocal radial to 30 degrees, that being 210. Then, draw a line perpendicular to the 30 degree radial. If the airplane is on the same side of that perpendicular line as the 30 degree radial then the airplane is on the “from” side of the 30 degree radial, but its also on the “to” side of the 210 degree radial. Let’s assume the aircraft is roughly where the 10 degree radial would be. If the question involves choosing which VOR face represents the aircraft’s position and it offers a VOR face reading 30 degrees at the top, with a “from” flag and the needle right, great. However, they might offer a 210 heading at the top with the flag reading “to” and the needle on the left. That would also be a correct answer. Avoid the tricks by adding the reciprocal radial and a line perpendicular to both radials.

There’s another trick style question that can be asked. You’ll see a drawing of a VOR station with a radial coming off it. The airplane will be on a line about 90 degrees to the radial that’s drawn in. There will be, say, four VOR faces. Three will show the radial that’s drawn in on the sketch dialed in to the top of the VOR face, with the only difference being the flag – it will read “from” on one, “to” on the second and “off” on the third. The needle will be offset on the “from” and “to” flagged diagrams and centered in the “off” diagram. The fourth VOR face will show a centered needle and the VOR will be dialed in to a radial exactly 90 degrees to the radial that’s drawn in, or a bearing that is the reciprocal of the radial that the aircraft is drawn in on. The trick is to make you assume that the radial drawn in the sketch is the radial that should be on the VOR. What they’re doing is giving you that radial as a reference. You can see pretty easily what radial the aircraft is on.

Ok, that’s all I’ve got on the VOR. Practice using it while flying, either with an instructor or on your solo flights. You need to practice the TiTs procedure of Tune, identify and test. The hardest part at first is identifying the correct morse code. Write it down on your knee board before the flight and then tap your finger on something in sequence with the dots and dashes. Practice that.

On the test draw in the reciprocal radials as well as a line across the VOR face at 90 degrees to the radial. This will let you determine whether the aircraft in the diagram is on the from or to side of the radial on the diagram, whether the radial on the diagram or it’s reciprocal is the one they’re setting the VOR face to, or whether they’re just giving you a drawn in radial for reference but setting the VOR on a different radial (probably one perpendicular to the drawn in radial so that it’s not too tricky).

So, get out there, do some flying, fool around with the VOR. Notice how you generally have to fly a slightly different heading to stay on the VOR track. Have some fun! Any questions, comments or suggestions can be sent to Bushpilotintraining.com, where you’ll find the show notes.

My name is Rob Chipman and I’m a realtor and pilot based in Vancouver, BC. I AM NOT A FLIGHT INSTRUCTOR AND I AM NOT OFFERING FLIGHT INSTRUCTION! I am sharing my study notes and other things I’ve learned while getting my education as a pilot. You’re welcome to make use of this information, but do not treat it as expert advice.

I really enjoy flying, real estate and the Chilcotin.  My company is Coronet Realty Ltd., located at 3582 East Hastings Street, Vancouver, BC, V5K 2A7. I have a C-150L that I own with two other pilots, based out of Pitt Meadows. Do not hesitate to contact me by email if I can help you do anything, especially if its likely to be interesting or concerns selling remote property in British Columbia.

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