VOR (Very High-Frequency Omnidirectional Range) navigation system

VOR is a critical component of aviation navigation, providing reliable guidance for aircraft through a network of ground-based transmitter stations. Here's a structured summary:

1. Overview

• VOR is a VHF radio-based system (108-117.95 MHz) that uses thousands of land-based transmitter stations across airways.
• Used to determine an aircraft's position and direction relative to the VOR station through 360° radials emitted from the station.
• Its VHF frequency minimizes atmospheric interference but limits usage to line-of-sight range.

2. System Components

Types of VOR Stations: TVOR (Terminal VOR):

• Positioned at airports for close-proximity navigation. VORTAC: Combined VOR and TACAN for both civil and military use.

Aircraft Equipment:

• Receivers decode phase differences between VOR signals to determine bearing to/from the station. Most aircraft use dual VOR receivers for redundancy. NAV/COM radios integrate VOR and VHF communication functions.

3. How It Works

• The VOR transmitter emits a reference signal and a rotating variable signal.
• The aircraft receiver detects phase differences to determine the radial or bearing relative to the station.
• Instruments like the Omni Bearing Selector (OBS), Course Deviation Indicator (CDI), and Radio Magnetic Indicator (RMI) help pilots navigate by showing deviation from the selected course.

4. Navigation Displays

CDI/OBS:

• Shows the deviation from the desired course, with graduation marks representing degrees.

HSI (Horizontal Situation Indicator), EFIS (Electronic Flight Instrument System), and EADI (Electronic Attitude Director Indicator):

• Advanced systems integrating VOR navigation with other flight data.

ILS Integration:

• At large airports, VOR stations may also support Instrument Landing Systems (ILS), utilizing the same receiver for both VOR and localizer signals.

5. Additional Systems

DME (Distance Measuring Equipment):

• Paired with some VORs, it provides precise distance information.

VOT (VOR Test Facility):

• Allows pilots and technicians to test VOR equipment accuracy. VOTs are located at airports and typically operate on 108.0 MHz.

• Ground-based and VOT testing help ensure VOR accuracy, with an allowable error of ±4°.
• Excessive error disqualifies the aircraft from IFR (Instrument Flight Rules) operations until resolved.

The VOR navigation system continues to be an essential part of IFR navigation and is integrated into modern cockpit systems, providing reliable, accurate guidance to aircraft operators.