More on the TO-FROM Flag

If you attempt to track a radial from the station, with a "TO" flag, the needle will work in reverse. The pilot would need to fly away from the needle, not towards it, in order to keep it centered. The same is true if flying to a station with a "FROM" flag. To alleviate this reverse sensing, make sure the TO-FROM flag displays the correct indication. If it does not, rotate the OBS until the desired flag appears.

The TO-FROM flag may also display an OFF indication. The OFF indication is shown when neither a TO or FROM indication is appropriate for the OBS selection, such as a selection that would take the airplane neither to nor from the station. It is also displayed with directly over or very close to the navaid. If none of these conditions do not exist, then the OFF flag indicates a loss of signal from the navaid.

VOR Sensitivity

Since the radials a VOR transmits all originate at the VOR station itself, the distance between radials increases the further the airplane is from the station. This means that the needle is slower to respond at greater distances from the VOR, since the airplane must move a greater distance to move from one radial to another. As the airplane gets closer and closer to the station, the needle will become more and more sensitive, making it more difficult to keep centered.

Full scale deflection of the CDI, when receiving a VOR signal, is about 10 to 12 degrees. Each dot on the display represents 2 degrees.

Radials diverge at a lateral distance of about 100 feet per mile from the station. This means you can approximate the distance required to fly between radials. For example, at 60 nm, the 180 and 181 degree radials are 6,000 feet apart. So, a one dot deviation at 60 miles, 2 degrees, represents a lateral course divergence of 12,000 feet.

When overflying a VOR, the needle will become more and more sensitive until, when very close to the navaid, the needle will likely swing all the way to the left or the right. At these close distances, simply remain on your heading. The TO-FROM flag will change from "TO" to an OFF indication during station passage. Once on the other side of the station, the "FROM" flag will appear.

As you track outbound from the station, the needle will become less and less sensitive with increasing distance from the VOR.

Intercepting a Radial

Often times, it is desirable to track a specific radial. To do so, dial the radial you desire to track using the OBS. Turn the airplane to a heading that is the same as the course you selected with the OBS. The airplane is now roughly paralleling your desired course.

Next, select a new heading, which will intercept the desired course. If the needle is not deflected to full scale, only a small heading change may be required, such as 15 or 30 degrees in the direction of the needle deflection. If the needle is deflected full scale, a greater intercept heading will be required.

You may choose to center the needle with a from indication to see which radial you're currently on, then return the OBS to the desired course. Choose an intercept heading, in the direction of the needle, between 30 and 90 degrees left or right of your current heading. When the needle begins to center, turn to the desired course. Track the desired radial, using the bracketing technique to correct for wind drift.