VOR Navigation

Introduction to Air Navigation Systems

Air navigation systems guide pilots along predetermined flight paths.

Types of navigation systems:

  • Aircraft-based systems (e.g., inertial navigation systems) that do not require external signals

  • Ground-based systems where ground radar monitors the aircraft's position and provides guidance

  • Combination systems utilizing both ground and airborne equipment (most common)

Ground equipment transmits signals to airborne receivers for navigation

Very High Frequency Omni-directional Range (VOR)

VOR is a widely used navigation system for pilots

Key concepts:

  • Operates in the very high frequency (VHF) range

  • Military uses TACAN (Tactical Air Navigation) in ultra-high frequency (UHF) range

  • VORTAC combines VOR and TACAN at the same site

VOR stations on sectional charts:

  • Symbol for VOR

  • Symbol for VORTAC

  • VOR frequencies shown in boxes near the station symbol

  • The compass rose around a VOR aligns with magnetic north, showing possible courses

Understanding radials and bearings:

  • Radials are magnetic courses extending FROM a VOR (e.g., 360° radial extends north)

  • Bearings are courses flown TO or FROM any point on the surface

  • Pilots can select from 360 radials for navigation

Using the VOR Receiver

Components of the VOR receiver:

  • Volume control and ident switch for station identification.

  • Frequency selector ranging from 108.0 to 117.95 MHz.

VOR indicator includes:

  • Omni Bearing Selector (OBS) to select courses

  • Course Deviation Indicator (CDI) showing position relative to the selected course

  • TO/FROM indicator showing whether the selected course takes you to or from the station

Understanding indications:

  • CDI needle deflects left or right indicating course deviation

  • Deflections are consistent regardless of aircraft heading

  • Needle centered means you are on the selected course

Navigating with the VOR

  • Determining your position:

  • Tune and identify a nearby VOR station

  • Rotate the OBS until the CDI centers with a FROM indication

  • Read the radial (course) from the OBS: your position is along this line from the VOR

  • Use a second VOR to intersect radials for exact position fixing.

Flying to a VOR station:

  • Tune and identify the desired VOR station.

  • Set the OBS to the desired inbound course (bearing TO the station).

  • Turn the aircraft to the selected course heading.

  • Keep the CDI centered by making small heading adjustments.

Flying from a VOR station:

  • After station passage, set the OBS to the desired outbound radial.

  • Turn the aircraft to the outbound course heading.

  • Maintain the course with the CDI centered.

Recognizing station passage:

  • The TO/FROM indicator flips when crossing the station.

  • A "cone of confusion" may occur directly over the station with fluctuating signals.

  • Use the first complete reversal of the TO/FROM indicator to confirm passage.

VOR Signal Limitations

1. Line-of-sight reception:

a. Signals can be blocked by terrain or Earth's curvature.

b. Reception range increases with altitude.

c. At 1,000 feet above the station, reception extends approximately 40 nautical miles.

2. Reception limitations:

a. Certain radials may be unusable below specific altitudes (refer to Chart Supplement).

b. Obstructions can cause signal anomalies like course roughness.

VOR Accuracy and Checks

1. Identifying VOR stations:

a. Listen for the Morse code identifier to confirm correct tuning.

b. A missing or altered identifier indicates maintenance:do not use the VOR.

2. VOR accuracy:

a. Accuracy is generally within ±1 degree if equipment is properly calibrated.

b. Both transmitter and receiver must be functioning correctly.

3. VOR receiver checks:

A. Ground checkpoints (allowable IFR error is ±4 degrees).

B. Airborne checkpoints (allowable IFR error is ±6 degrees).

C. VOR Test Facilities (VOT):

a. Transmit the 360° radial in all directions.

b. CDI should center on 360° FROM or 180° TO with an allowable error of ±4 degrees (IFR).

4. Equipment maintenance:

a. Regular calibration of VOR receivers is recommended (annually).

b. Ensure reliability of navigation instruments for accurate flying.

Distance Measuring Equipment (DME)

1. Overview of DME:

a. Provides distance information to the station.

b. Installed in many civilian aircraft.

c. Measures time for signal round trip to calculate distance.

2. VOR-DME and VORTAC stations:

a. VOR-DME combines VOR navigation with DME distance information.

181

b. VORTAC combines VOR and TACAN facilities for civilian and military use.

c. Symbols are indicated on sectional charts.

3. Using DME:

a. Eliminates need for cross-fixes with multiple VORs.

b. Provides real-time distance to the station.

c. Some units display ground speed and estimated time to station.

Conclusion

1. VOR navigation is essential for pilot proficiency.

2. Understanding and correctly using VOR ensures safe and accurate navigation.

3. Regular equipment checks and maintenance are crucial for reliability.

4. Always be aware of navigation aids, their limitations, and proper usage.