Understanding VOR Checks – What You Need to Know
VOR checks are a cornerstone of aviation safety—a mandatory ritual that every instrument-rated pilot must master. These critical inspections verify that your aircraft’s VOR (VHF Omnidirectional Range) navigation equipment maintains the precision demanded by instrument flight conditions. Federal Aviation Regulation (FAR) 91.171 is clear: pilots must complete a VOR check within 30 days of any IFR flight.
Why such stringent requirements? The reason is simple: The FAA mandates VOR equipment accuracy within ±4 degrees for ground checks and ±6 degrees for airborne verification. Exceed these tolerances, and you risk significant course deviations that compound exponentially over distance.
Pilots can choose from several FAA-approved verification methods:
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NOT (VOR Test Facility): A ground-based signal simulating a VOR station.
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Ground Checkpoints: Designated locations on an airport with a published radial.
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Airborne Checkpoints: Published points defined by a radial from a VOR.
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Dual Receiver Comparison: Cross-checking two independent VOR receivers in the same aircraft.
Documentation is required—every check must be logged in the aircraft’s maintenance records, creating an audit trail that proves regulatory compliance.
FAA Regulations on VOR Checks – FAR 91.171
Federal Aviation Regulation 91.171, part of Title 14 of the Code of Federal Regulations (14 CFR), provides the legal foundation for VOR equipment verification. It mandates that no pilot may fly under IFR using VOR navigation unless the equipment has passed an accuracy check within the preceding 30 days.
FAR 91.171 is aviation law. This regulation, embedded within Title 14 of the Code of Federal Regulations (14 CFR), establishes the legal foundation for VOR equipment verification. The 30-day window strikes a careful balance: frequent enough to catch equipment drift, yet practical enough to avoid operational paralysis.
Compliance extends beyond the check itself. FAR 91.171 requires careful documentation—each VOR verification must be recorded in the aircraft’s maintenance records. These are legal documents that matter during FAA ramp checks. Missing or incomplete records? You’re grounded, regardless of whether your equipment actually works.
VOR Accuracy Requirements – Tolerances Explained
These tolerance limits are carefully engineered safety margins. Consider this: a seemingly minor 5-degree error at 60 nautical miles translates to a lateral displacement of approximately 5.2 nautical miles. In mountainous terrain or congested airspace, that deviation could be dangerous.
Experienced pilots don’t wait for equipment to fail. Regular calibration and proactive maintenance prevent problems. If your VOR consistently flirts with tolerance limits, that indicates your equipment needs attention. Address it before you’re explaining to the FAA why your “technically compliant” receiver led you astray.
Types of VOR Checks – Methods and Procedures
VOR systems are essential for instrument flight—guiding aircraft along Victor Airways and Jet Routes while guiding them through Stars, departure procedures, and non-precision approaches. Without reliable VOR navigation, the entire IFR system would collapse.
Many pilots don’t realize that VOR stations aren’t all created equal. You’ll encounter standard VOR installations, VOR TAC facilities (combining VOR with military TACAN), and VOR/DME combinations. Each offers unique capabilities, but your receiver verification requirements remain identical regardless of the ground station type.
NOT Check Method – Step-by-Step Guide
The NOT check is the most reliable VOR verification method—precise, controlled, and straightforward. This method uses a specialized ground-based test signal that creates a virtual VOR station directly beneath your aircraft. Here’s how to perform a NOT check:
Position your aircraft carefully. Park your aircraft in a designated NOT reception area, steering clear of hangars and metal structures that can interfere with signal quality. Choose an open area for best results.Set the correct frequency. Dial in the published NOT frequency from your Airport/Facility Directory or Chart Supplement. These frequencies typically inhabit the 108-112 MHz spectrum—double-check to avoid embarrassing mistakes.Listen before you leap. Crank up the audio volume and confirm you’re receiving the NOT’s distinctive Morse code identifier. No identifier? You’re either on the wrong frequency or facing equipment issues.Center the needle carefully. Slowly rotate your OBS until the CDI needle finds perfect center. Take your time—rushing this step undermines your entire check.Check the TO/FROM indicator. With your needle centered, verify the TO/FROM indicator behavior: “FROM” at 0° and “TO” at 180°. This critical verification confirms your receiver’s internal logic remains sound.Check the tolerance limits. Your OBS must read either 0° (±4°) with FROM indication or 180° (±4°) with TO indication. Anything outside these boundaries means maintenance before your next IFR adventure.Document the check. Record every detail—date, location, bearing error, and your signature. This documentation protects you during regulatory inspections.
NOT checks work well because they eliminate variables that affect other methods. You’re testing against a known, controlled reference—no atmospheric interference, no station maintenance issues, no geometric complications. When available, NOT should be your first choice.
Township and Dual Receiver Checks – How They Work
When NOT facilities aren’t available, dual receiver checks provide an alternative. This method uses the redundancy built into most IFR aircraft, turning your backup systems into verification tools.
To perform a dual receiver check:
Set both receivers to the same frequency. Tune both VOR units to identical frequencies, then verify station identity through Morse code confirmation. Mismatched stations will sabotage your entire effort.Set the same course on both OBS units. Set identical courses on both OBS units. Your current radial often provides optimal signal strength, though any radial will suffice.Check for agreement. Your CDI needles or bearing pointers must align within ±4 degrees. Greater discrepancy signals trouble—at least one receiver needs professional attention.Verify the TO/FROM indicators. TO/FROM indicators should mirror each other perfectly. Conflicting indications indicate maintenance is needed.
Dual receiver checks offer flexibility—perform them airborne or ground-bound, at your home airport or halfway across the continent. This versatility makes them invaluable during extended cross-country operations.
However, dual checks reveal relative accuracy, not absolute precision. If both receivers drift identically, you’ll never know. That’s why periodic NOT or checkpoint verification remains essential for maintaining navigation integrity.
Logging Your VOR Checks – Documentation Requirements
Documentation transforms your VOR check from a maintenance task into legal compliance. Every verification must include these non-negotiable elements:
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Date: The date the check was performed.
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Place: The location and method used (e.g., NOT, ground/airborne checkpoint name).
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Bearing Error: The specific deviation observed in degrees.
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Signature: The signature of the pilot who conducted the check.
Pilots should develop systematic documentation habits. Some maintain dedicated VOR logbooks; others integrate records into existing maintenance logs. Both approaches work—consistency and completeness matter more than format. Digital systems gain popularity, but traditional paper records remain perfectly acceptable.
What to Include in Your VOR Check Log
Creating a thorough VOR check log requires attention to specific details that satisfy both regulatory requirements and practical needs. While the previous section outlined the essential elements, let’s examine each component more closely to ensure your documentation is complete and effective.
Date precision eliminates confusion and establishes your 30-day compliance window. Use standard MM/DD/YYYY format—ambiguous dating invites regulatory complications during inspections.
Location specificity demonstrates professionalism and aids troubleshooting. Consider these examples:
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If using a NOT: Record the airport identifier and “NOT” (e.g., “KBS NOT”)
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If using a ground checkpoint: Note the airport identifier and checkpoint designation (e.g., “WORD Checkpoint Alpha”)
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If using an airborne checkpoint: Document the navies identifier and your position (e.g., “BOS VOR, 10 NM east at 3,000 feet”)
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If using dual receivers: Specify “Dual Receiver Check” and the VOR station used
Bearing error documentation should capture exact deviations, not simple pass/fail assessments. Recording “OBS reading 356° with published radial of 360° = 4° error” creates valuable historical data that might reveal gradual equipment degradation patterns.
Your signature establishes accountability and qualification. Include your full name and pilot certificate number—some pilots add certificate type (ATP, Commercial) for additional credibility.
Consider supplementing required information with aircraft tail number, receiver specifications, and signal quality observations. This additional context proves invaluable for maintenance tracking and future troubleshooting efforts.
Common VOR Check Errors – Troubleshooting Tips
Even seasoned pilots stumble during VOR checks. Recognizing these common pitfalls—and knowing their solutions—separates competent aviators from those who learn through expensive mistakes.
Common VOR check errors include:
TO/FROM indications are simple in concept but can confuse pilots. When your receiver displays “TO,” you’re positioned such that flying your selected OBS course leads toward the VOR station. “FROM” means the opposite: your selected course takes you away from the facility.
This directional information is valuable during IFR operations. Intercepting airways becomes intuitive—the TO/FROM indicator instantly confirms whether you’re flying inbound or outbound relative to the station. No mental gymnastics required.
Where pilots get confused: TO/FROM indications ignore your actual heading entirely. They reflect only the relationship between your OBS setting and the VOR radial. Flying north while showing “TO” doesn’t mean you’re physically approaching the station—it means your selected course would take you there.
In practice, When cleared to intercept V123 westbound, a TO indication with westbound OBS setting confirms you’re positioned correctly to proceed along the airway. Simple. Reliable. Effective.
During partial panel emergencies or primary display failures, TO/FROM indicators become lifelines. These humble lights provide essential orientation when sophisticated systems fail, helping you navigate safely home when technology abandons you.