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VOR Navigation

VHF Omni-directional Range — principles, operational checks, and procedures.

Quick Reference

Key points

Short-answer refresher for returning pilots before diving into the full page.
  • A VOR radial tells you where you are from the station, and the TO/FROM flag tells whether that selected course is inbound or outbound.
  • Station passage, receiver checks, and changeover points deserve deliberate attention because VOR navigation is geometry plus signal management.
  • Use small wind corrections to hold the course and verify the station and course logic before treating the CDI as self-explanatory.

Standards & References

FAA doctrinal and ACS cross-reference

Use this box to line the topic up with the FAA’s primary instrument handbooks, the most relevant ACS task areas, and the knowledge, skill, and risk elements that usually drive checkride evaluation.

Instrument Rating Airplane ACS unless noted
IFH
  • IFH Ch. 9, IFR Flight: intercepting, tracking, and managing navigation sources while flying airways, arrivals, and approaches.
  • IFH Ch. 4, Flight Instruments: CDI/HSI interpretation supporting VOR tracking accuracy.
IPH
  • IPH Ch. 2, En Route Operations: airway structure, fixes, and ground-based navigation use in the IFR system.
  • IPH Ch. 4, Approaches: VOR-based nonprecision approach execution, radials, fixes, and MAP awareness.
ACS Task References
  • V.A Intercepting and Tracking Navigational Systems and DME Arcs.
  • VI.A Nonprecision Approach.
On This Page

A VHF Omni-Directional Range (VOR) is a short-range radio navigation system that provides bearing information to aircraft. Ground stations transmit a reference and variable signal; the airborne receiver compares their phase to determine the radial (bearing) from the station. Pilots use VOR radials to establish courses, intercept and track airways, and form fixes when used with distance or cross-bearing techniques.

Overview

VORs provide bearing information to and from ground stations operating in the VHF frequency band (108.0–117.95 MHz). They are used for en route navigation along Victor airways, as initial approach fixes, and as missed approach holding points. Despite the growing use of GPS/GNSS, VORs remain a primary backup navigation system in the U.S. National Airspace System.

Principles

The VOR ground station transmits two signals simultaneously: a reference signal (omnidirectional) and a variable signal (rotating). The phase difference between these two signals corresponds to the aircraft's magnetic bearing from the station (the radial). The airborne receiver measures this phase difference and displays the result on the course deviation indicator (CDI) or HSI.

Equipment

Aircraft and ground station equipment, indicators, and displays used with VOR systems.

  • VOR receiver: Tuned to the station frequency; identifies the station via Morse code identifier.
  • CDI (Course Deviation Indicator): Displays selected course (OBS setting) and deflection from that course.
  • HSI (Horizontal Situation Indicator): Combines CDI with heading indicator for improved situational awareness.
  • RMI (Radio Magnetic Indicator): Shows the bearing pointer to the station relative to the aircraft's magnetic heading.

VOR Operational Check

Prior to flight (or as required by the operator), perform a VOR operational check to verify receiver accuracy and identification. This can be completed using one of the following approved methods:

  • VOT Check: Tune the VOR to the VOT frequency and center the CDI; the receiver should indicate 0° or 180° with correct TO/FROM indication.
  • Ground Check: Use a designated ground VOR test facility and verify the indicated radial within allowable error.
  • Airborne Check: Overfly or track to/from a VOR with known bearing and compare the indicated radial to the expected bearing within tolerances.
  • Frequency: For IFR operations, many operators perform VOR serviceability checks at least every 30 days.
Tolerance
  • VOT, ground test signal, or designated surface checkpoint: Maximum permissible indicated bearing error is ±4° (see § 91.171(b)(1)-(2)).
  • Airborne checkpoint: Maximum permissible indicated bearing error is ±6° (see § 91.171(b)(3)-(4)(iii)).
  • Dual independent VOR systems: Maximum permissible variation between the two indicated bearings is ±4° (see § 91.171(c)).
Recordkeeping
  • Date: The date the operational check was performed.
  • Place: The location where the check was performed (airport, VOT, or specified checkpoint).
  • Bearing error: The observed bearing error recorded in degrees.
  • Performed by: Name and signature of the person who performed the check.
Sample Log Entry
Date: 2025-11-18
Location: (Airport / VOT / Checkpoint)
Method: VOT / Ground Check / Airborne Check
VOR Station: (Identifier)
Indicated Bearing Error: +/- X°
Checked By: (Name, Certificate)
Notes: (e.g., TO/FROM indication, CDI centered, any discrepancy)
Regulatory Reference

Regulatory requirement: 14 C.F.R. § 91.171 — VOR equipment must be operationally checked within the preceding 30 days for IFR operations.

Operation

How pilots use VORs: tuning, identification, radial interception, tracking, and station passage.

  • Tune & identify: Tune to station frequency and confirm Morse code or voice identifier before use.
  • Select course: Set the OBS to the desired course or inbound/outbound radial.
  • Intercept: Fly headings to intercept the selected radial; use CDI deflection and TO/FROM indication to judge position.
  • Track: Maintain the selected radial by bracketing wind correction; monitor CDI for course deviations.
  • Station passage: Identified by TO/FROM flag flip and momentary CDI fluctuations as the aircraft passes over or abeam the station.

Limitations

  • Line-of-sight: VOR signals are line-of-sight; low altitude and terrain can block reception.
  • Range: Varies with altitude and station class (Terminal ~25 NM, Low 40 NM, High 130+ NM at high altitude).
  • Cone of confusion: Directly overhead a VOR, signal quality degrades and CDI/flag fluctuate.
  • Interference: Co-channel or adjacent-channel interference can cause erratic indications in congested frequency areas.
  • Accuracy degradation: Mountainous terrain, nearby buildings, and aircraft attitude can cause scalloping.

Signal & Accuracy

VOR accuracy classes are defined by the FAA: Terminal (T), Low (L), and High (H) altitude VORs each have defined service volumes. The FAA requires VORs to maintain signal accuracy within ±1° at the antenna. Receiver accuracy requirements are ±4° for IFR-approved equipment. Pilots should verify signal quality by monitoring the station identifier and TO/FROM flag.

Procedures

Common procedures using VORs: approaches, departures, and airway navigation examples.

  • Victor airways: Defined by VOR radials; fly the published course between stations using the CDI.
  • VOR approaches: Use published approach plates; fly final approach course inbound, track the CDI, and execute missed approach per published instructions.
  • Holding: VOR fixes serve as common holding points; enter holds per AIM holding entry procedures using the inbound radial as reference.

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