Overview

Basic description of VOR, history, and common uses in navigation and procedures.

Principles

Explain how phase difference between reference and variable signals produces bearing information.

Equipment

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

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: Perform checks before flight when required by operations or maintenance procedures; for IFR operations, many operators perform/verify VOR serviceability checks at least every 30 days (or as specified by aircraft/equipment manufacturer and regulations).

Tolerance

• VOT, FAA/approved ground test signal, or designated surface checkpoint: Maximum permissible indicated bearing error is ±4° (see § 91.171(b)(1)-(2)).
• Airborne checkpoint or in-flight over a prominent ground point (when no ground test/checkpoint is available): Maximum permissible indicated bearing error is ±6° (see § 91.171(b)(3)-(4)(iii)).
• Dual independent VOR systems: When one system is checked against the other, the maximum permissible variation between the two indicated bearings is ±4° (see § 91.171(c)).
• If out of tolerance: The VOR should not be relied upon for IFR navigation until the source of the error is corrected and the check is repeated and recorded per maintenance/operator procedures.

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 (e.g., ±X°).
• Performed by: Name and signature of the person who performed the check (and certificate/authorization, if applicable).
• Repair-station test signal: If a repair-station test signal was used, include the repair station identification and attestation/signature as required by the regulation.

Regulatory Reference

Regulatory requirement: 14 C.F.R. § 91.171 — VOR equipment must be operationally checked within the preceding 30 days for IFR operations. See the referenced regulation for required check methods and permissible bearing error limits.

Further Reading

For detailed procedures and operational guidance, see the Instrument Flying Handbook (FAA-H-8083-15): FAA-H-8083-15 — Instrument Flying Handbook (PDF).

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)
                    

Operation

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

Limitations

Range, line-of-sight, cone of confusion, and interference factors affecting VOR performance.

Signal & Accuracy

Typical VOR signal structure, accuracy classes, and monitoring.

Procedures

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