The Omni-Bearing Indicator
The VOR indicator (or "VOR head") on the instrument panel includes a dial called the omni-bearing selector (OBS) or omni-bearing indicator (OBI); a needle or course deviation indicator (CDI) that pivots at the top like a windshield wiper or moves smoothly from side to side; and an ambiguity indicator, or TO-FROM-OFF flag.

Answer One
The first question is answered by rotating the OBS until the needle centers and the ambiguity indicator shows FROM. The reading at the top of the OBI now shows which radial you're on. For example, suppose the needle is in the center with a FROM indication. If the reading at the top of the OBS is 270, you're somewhere along a line due west of the station. A reading of 150 puts you along a line southeast of the station, and a reading of 030 means you're northeast of the station.

Answer Two
To find your way to a VOR station, change the course in the OBI until the ambiguity indicator shows TO and the needle centers. The reading at the top of the OBI is the magnetic course you should fly to go directly to the station. For example, if the indicator says 090 in this situation, turn to a heading of due east, and you'll go right to the station.

Answer Three
The third question assumes that you want to intercept a specific radial, often an airway running between two VORs on a chart. Suppose the airway you want to fly between VOR A and VOR B has a course of 067 degrees.

To fly away from VOR A on that airway, tune VOR A on one of the navigation receivers. Change the OBS setting to 067. The ambiguity indicator should show FROM, and the needle will be deflected to one side. If the needle is deflected to the left, you should fly a heading to the left of 067 degrees to intercept the radial. A 30-degree intercept angle is a good starting point, so turn your airplane to a heading of 037 degrees and hold that heading until the needle on the OBI moves toward the center. As the needle centers, smoothly turn to a heading of 067 degrees.

If there is a crosswind, the needle will soon drift off-center (needles always move into the wind) and you must adjust your heading toward the needle (into the wind) until it drifts back to the center position. You will soon settle on a heading slightly into the wind that keeps the needle centered.

Inbound on the Radial
Things get a bit more complicated about halfway along your trip to VOR B. At that point you should tune in VOR B, because you're likely to lose the signal from VOR A.

Airways are defined by radials, which always go away from VORs. If you want to fly to VOR B at this point, you must use the reciprocal of the radial you want to fly.

Assume the airway between A and B is labeled 247 degrees as it approaches VOR B. To fly toward VOR B on that radial, you must select the reciprocal of 247 degrees, or 067 degrees, as the course on the OBI. Check that the OBS is set to 067 degrees and continue. Expect the needle to become more sensitive as you approach VOR B. As you fly over VOR B, the ambiguity indicator will change from TO to FROM.


Determining Your Position With Two VORs
If you are uncertain of your position, you can determine your position by using two VORs simultaneously.

Tune in two VORs that you expect to be within range. Change the setting on the OBI of each VOR receiver until each needle is centered and both flags show FROM. The indication at the top of each OBI tells you which two radials you're on.

Your airplane is at the point where the two radials intersect.

You can find an HSI in the cockpit of the Boeing 737-400 in Flight Simulator.

Bird's-Eye View
The HSI shows you a top-down view. Your airplane is at the center of the instrument. Your magnetic heading is at the top. The omni-bearing selector is a yellow arrow with a central segment that moves back and forth and acts as a course deviation indicator. A white triangle near the center replaces the TO-FROM-OFF flag. It points toward the VOR station.


Using the HSI
You can use the horizontal situation indicator (HSI) on the 737-400 or Learjet 45 instrument panel for en route navigation along VOR radials or to guide you down an ILS approach.

Intercepting a VOR Radial
Interpreting your position relative to a VOR station and a selected radial is easy with an HSI.

Tune in a VOR station on the NAV 1 radio, which is connected to the HSI. In the Learjet 45, make sure the VOR 1 information is visible next to the HSI. If it isn’t, click the VOR select knob at the bottom of left of the HSI panel to select the VOR 1 display.

Select the course you want to fly on the autopilot panel in the section marked "course." As you change the course setting, the yellow arrow moves around the face of the instrument.

When you've selected the course, turn toward the head of the yellow needle. As you turn, the heading indicator portion of the HSI rotates. The center part of the needle will be deflected to one side. Keep turning until the center part of the needle and an imaginary line running top to bottom through the HSI form a 30–45-degree angle. Hold that heading, and the center portion of the needle will gradually move to the middle of the HSI. As the needle centers, slowly turn away from the needle to make a smooth intercept.

Flying an ILS
The HSI has built-in localizer and glide slope indicators that make it easy to fly an ILS approach because most of the information you need is in one place.

Tune the ILS frequency into the NAV 1 radio.

Select the localizer course (usually the runway heading) on the autopilot panel in the section marked "course." As you change the course setting, the yellow arrow moves around the face of the instrument.

Intercept the final approach course just as you would a VOR radial—but keep in mind that a localizer is much more sensitive, so use small corrections.

On the Boeing 737-400, the glide slope indicator is a yellow diamond shape that moves up and down along a vertical scale on the right side of the HSI. On the Learjet 45, the glide slope indicator is a white pointer that moves along a vertical scale. If the glide slope marker is above the center, you're below the glide slope. If it's in the lower half of the vertical scale, you're above the glide slope.

VOR Approaches
A VOR approach is a nonprecision approach. Almost all VOR approaches have visibility minimums of about 1 mi (1.6 km) for small, relatively slow airplanes such as the Cessna Skylane RG. Minimum descent altitudes are determined by the local terrain and other factors, but they are usually 500–600 ft (152183 m) AGL.

Two Situations
When ATC can't vector you to the final approach, you must fly the entire approach procedure on your own. Most VOR approaches fall into two categories.

The VOR facility is located at the airport and serves as both the initial approach fix (IAF) and the final approach fix (FAF).

The VOR is located at some distance from the field and may or may not be the final approach fix.

Situation Number One
Assuming the first situation, you must fly over the facility, reverse course in what's called a procedure turn, and then track inbound to the VOR on the published radial while descending to the minimum descent altitude. The missed approach point is usually the VOR, so you don't need to keep track of elapsed time as you fly the approach. If you can't find the VOR, you won't be able to find the airport.

Situation Number Two
There are many variations of the second situation. The most common requires that you fly over the VOR, fly outbound at a published minimum altitude while reversing course, and then track inbound to the VOR while maintaining a published altitude.