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I'm working through the ASA Private Pilot 2020 Test Prep questions and there's a question I don't understand the answer for.

3579 (Refer to Figure 28, illustration 5) The VOR receiver has the indication shown. What radial is the aircraft crossing?

  • A - 030
  • B - 210
  • C - 300

Figure 28, illustration 5

I thought the answer was B - 210 but that is the heading, not the crossing.

The correct answer is A - 030, but I'm not sure why. What does it mean to be crossing a radial?

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    $\begingroup$ 210 is NOT the heading. That instrument has no heading information available to the pilot. It only allows the pilot to select a desired track to or from a VOR station. $\endgroup$ – Mike Sowsun Sep 8 '20 at 16:34
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A radial is always pointing (radiating) away from the VOR. But your instrument shows the TO/FROM indicator as TO. So you are crossing a 210 course towards the VOR, which means you are on the 030 radial from the VOR.

What does it mean to be crossing a radial?

This just refers to the fact that you cannot determine your heading (or track) from the CDI. Based on this instrument alone, you could be following the track to VOR right now or just happen to cross the radial at this moment (but actually fly in a totally different direction).

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    $\begingroup$ Another term (not necessarily an aviation term) for this would be the reciprocal bearing. $\endgroup$ – Davidw Sep 9 '20 at 5:35
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Radials radiate outwards from a station, just like the magnetic bearings on a compass rose. So, the outward radial is just the reciprocal of the inbound bearing.

The key is the “TO” flag. If you were to be flying a heading of 210 degrees you would fly TO the navaid.

Draw it out on a piece of paper, or refer to a chart or your study material. Orientation questions like this benefit most from visuals.

Also, don't get confused thinking this instrument is a gyroscopic compass card. It is not slaved to any inputs, the course showing on the face is manually dialed in and remains as set until you change it.

“Crossing a radial” simply means that you are not tracking along it either inbound or outbound to/from the navaid. (You are going across it at some angle.) This is a useful technique for identifying intersections if you have two VOR receivers: With one dialed in to the radial you are tracking, set the other one to the other VOR station that defines the fix, and dial in that radial on your OBS. When the CDI bar centers up it means you are crossing that radial.

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