VOR and DME - ATP Flight School

Question 1

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What does VOR stand for?

Answer 1

Very High Frequency (VHF) Omnidirectional Range

Question 2

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What does DME stand for?

Answer 2

Distance Measuring Equipment

Question 3

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What is TACAN?

Answer 3

Tactical air navigation equipment, basically the military equivalent of a VOR/DME.

Question 4

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Can civilians use TACAN?

Answer 4

Only the distance component, which is functionally identical to DME. (TACAN is often colocated with VORs to create VORTACs.)

Question 5

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What is a radial?

Answer 5

A straight-line course extending outwards from a VOR.

Question 6

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Describe the radio signals emitted by a VOR.

Answer 6

The VOR transmits signals in all directions (hence “omnidirectional”). The signal in each direction is different, so the VOR receiver can detect which radial it is on.

Question 7

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How are radials referenced/named?

Answer 7

By the number of degrees clockwise from magnetic north. For example, a course extending due east from a VOR would be the “zero niner zero radial.”

Question 8

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What radio frequencies do VORs use?

Answer 8

108.0 MHz to 117.95 MHz.

Question 9

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What is the standard useful range for a VOR below 14,500’ MSL?

Answer 9

25 NM for terminal VORs, 40 NM for low- or high-altitude VORs

Question 10

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Why might a particular VOR have a lower useful range on certain radials or at certain altitudes?

Answer 10

VOR signals are line-of-sight. You can’t pick up a VOR signal if there is terrain between the receiver and the ground station.

Question 11

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What are some ways to test the accuracy of your VOR receiver?

Answer 11

• VOR test facilities (VOTs)
• Certified airborne checkpoints
• Certified ground checkpoints
• Dual VOR cross-check

Question 12

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Are VOR checks required for VFR flight?

Answer 12

No (they’re only required for IFR), but they’re a good idea.

Question 13

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How do you confirm that you are receiving the correct VOR?

Answer 13

Listen for the VOR’s 3-letter identifier being broadcast in Morse code. (The dot-dash sequence to listen for is listed on the sectional chart.)

Question 14

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List three navigation instruments you might find in the cockpit that can display VOR navigation information.

Answer 14

• Course deviation indicator (CDI)
• Horizontal situation indicator (HSI)
• Radio magnetic indicator (RMI)

Question 15

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What is an OBS?

Answer 15

Omnibearing selector - the control knob that the pilot turns to select a desired radial.

Question 16

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What does the CDI needle indicate?

Answer 16

Assuming the aircraft is flown on the course selected on the OBS, is the selected radial to the left or right of the aircraft? The needle represents the course, so if the radial is to the left, the needle deflects to the left.

Question 17

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What is reverse sensing?

Answer 17

If you mistakenly enter on a CDI the reciprocal of your intended course, the needle deflection will reverse - e.g. if you are off-course to the left, the needle will deflect left (instead of right).

Question 18

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Why is a VOR receiver susceptible to reverse sensing?

Answer 18

The VOR receiver has no way of knowing the aircraft’s heading, only the bearing from the station.

Question 19

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What does the TO/FROM indicator on a CDI indicate?

Answer 19

Assuming the aircraft is flown on the course selected on the OBS, will it get closer TO or further FROM the VOR?

Question 20

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If the CDI needle is deflected by 1 dot, how far is the aircraft off the selected radial?

Answer 20

2 degrees

Question 21

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At what distance from the VOR does 1 degree off course equal 1 nautical mile off course?

Answer 21

60 nautical miles

Question 22

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How is an HSI different from a CDI?

Answer 22

An HSI combines a CDI and a heading indicator. In a CDI, the selected course is always at the top of the dial, regardless of the aircraft’s heading. In an HSI, the dial rotates so that the aircraft’s heading is at the top. The course deviation bar rotates with the dial, rather than staying vertical. This makes it easier to visualize the aircraft’s course relative to the selected VOR radial.

Question 23

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What information does an RMI display?

Answer 23

The aircraft’s heading, and the heading to two selected navaids or waypoints.

Question 24

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How do you determine which VOR radial you are on?

Answer 24

1. Tune and identify the VOR.
2. Twist the OBS knob until the needle centers with a FROM indication.
3. The number under the course index is the radial you are on.

Question 25

# ATPFlightSchool.com If you track a radial to a VOR, what indications should you expect as you overfly the VOR station?

Answer 25

As you near the station, the needle will become more sensitive (a given distance off course translates to a larger angle off course when closer to the VOR). It may start fluctuating side to side, and eventually the NAV flag will appear when you are directly over the station (where the signal is unreliable). Once past the VOR, the TO/FROM indicator flips to FROM, and the needle will re-center.

Question 26

# ATPFlightSchool.com You are on the 180 radial from a VOR and want to fly to the VOR, so you fly a heading of 360. As you do so, the CDI needle gradually deflects to the left. What is happening and what should you do?

Answer 26

A crosswind from the left is blowing you off course, and you need to establish a wind correction angle to the left: 1. Turn about 20° left to re-intercept the radial. 2. Once the needle is centered again, turn back to the right, but not all the way to 360 - leave a correction angle. 3. Hold that heading and see what the needle does. If it deflects left again, you need a bigger correction angle, and vice versa. 4. Repeat this process until you find a heading that keeps the needle centered.

Question 27

# ATPFlightSchool.com Describe the process for intercepting and tracking a VOR radial that you aren't currently on.

Answer 27

1. Tune and identify the VOR. 2. Turn to parallel the desired course. 3. Use the CDI to determine which radial you are currently on. 4. Take the difference between your current radial and desired radial. 5. Double the difference to determine the interception angle. If this angle is less than 20°, use 20°. If it is more than 90°, use 90°. 6. Twist the OBS knob to your desired course. 7. Turn left or right (towards the needle) by your interception angle. 8. Wait for the needle to approach center, then turn to track the desired radial.

Question 28

# ATPFlightSchool.com How does DME measure distance?

Answer 28

The receiver in the aircraft sends a radio signal to the unit on the ground, which then sends a signal back to the aircraft. The signal travels at the speed of light, so by measuring the time between sending and receiving the signal, the DME receiver can calculate the distance to the station.

Question 29

# ATPFlightSchool.com Explain the concept of "slant range."

Answer 29

DME measures the straight-line distance between the aircraft and the ground station, not the distance over the ground. This distance is affected by the aircraft's altitude. If you flew directly over a VORTAC at an altitude of 6,076' AGL, the DME would indicate 1.0 NM.

Question 30

# ATPFlightSchool.com How do you enter the frequency for a DME?

Answer 30

The UHF radio frequencies used for DME are paired with VHF frequencies used by VORs. Dialing in the VOR frequency automatically enters the paired DME frequency as well.

Question 31

# ATPFlightSchool.com ATP's aircraft do not have DME. Instead, they use...

Answer 31

GPS.