Direct Answer — The 30-Day VOR Check and Its Record
Under 14 CFR §91.171(a), no person may operate a civil aircraft under IFR using VOR unless the VOR equipment is maintained, checked, and inspected under an approved procedure, or has been operationally checked within the preceding 30 days and found to be within the limits of the permissible indicated bearing error. The accepted operational-check methods and their tolerances are set in §91.171(b) and (c): a VOT or repair-station test signal and a designated ground checkpoint are each ±4 degrees; a designated airborne checkpoint and the airborne-over-a-landmark method are each ±6 degrees; and a dual independent VOR system checked against itself is ±4 degrees between the two indicated bearings. Whatever method you use, §91.171(d) requires the person making the check to record exactly four things — the date, the place, the bearing error, and a signature — in the aircraft log or other record. A check older than 30 days, or one with no record, makes the aircraft ineligible to operate IFR using VOR until a fresh check is performed and logged.
This is a rolling 30 days from the check date — not a calendar-month interval
Unlike the 24-calendar-month altimeter and transponder tests, the §91.171 VOR check uses the phrase "within the preceding 30 days." That is counted forward from the date of the check itself — a check performed on June 13 is good through July 13, not through the end of July. For a working IFR aircraft this means the VOR check comes due more than a dozen times a year, which is exactly why it is so easy to let slip without a tracked next-due date.
The Rule — When §91.171 Is Triggered and the Two Compliance Paths
14 CFR §91.171(a) is triggered by a specific combination: operating a civil aircraft under IFR using VOR for navigation. When that is the case, the VOR equipment must satisfy one of two compliance paths before the flight.
The VOR equipment is maintained, checked, and inspected under an approved procedure. This is the path most large operators use — the VOR-check obligation is folded into an approved maintenance or inspection program rather than handled as a discrete 30-day pilot check. If you are on this path, the program defines how and when the equipment is verified, and the program records are the evidence.
The VOR equipment has been operationally checked within the preceding 30 days and found to be within the limits of the permissible indicated bearing error. This is the path most owner-operators and smaller flight departments use, and it is the one that produces the familiar pilot-logged VOR check entry. The rest of §91.171 — the methods, the tolerances, and the four-item record — describes how this operational check is done and documented.
The VOR check is about navigation-equipment integrity, not currency
The VOR receiver is the navigation equipment that has to be "suitable for the route to be flown" for IFR under §91.205(d)(2). The §91.171 check is what demonstrates that the installed VOR is reading bearings accurately enough to be relied on under instrument conditions. It is an equipment check on the aircraft — entirely separate from a pilot's own instrument currency, which lives in the pilot's records, not the aircraft's.
Because the VOR check is an equipment record rather than a maintenance entry, it sits apart from the airframe maintenance logs — see the Part 91 aircraft records requirements for how the various aircraft records fit together, and the aviation records retention schedule for how long each category is kept.
The Accepted Check Methods and Their Exact Tolerances
Section 91.171 lists the operational-check methods in paragraphs (b)(1) through (b)(4), plus the dual-VOR method in paragraph (c). The permissible bearing error is not the same for every method — ground-based and test-signal methods are tighter (±4°) than the airborne methods (±6°). Using the wrong tolerance against the wrong method is a quiet way to log a "passing" check that should have failed.
Use an FAA-operated or FAA-approved test signal — the VOR test facility (VOT) — or a test signal radiated by an appropriately certificated radio repair station. The maximum permissible bearing error is plus or minus 4 degrees. When a repair station radiates the signal, the repair station must certify the bearing it transmitted for the check and the date of transmission.
Use a VOR system checkpoint on the airport surface that has been designated for that purpose. The maximum permissible bearing error is plus or minus 4 degrees. These ground checkpoints are charted/published, with the assigned radial and the physical spot to position the aircraft.
Use an airborne checkpoint that has been designated for the purpose. The maximum permissible bearing error is plus or minus 6 degrees — the airborne methods carry a wider tolerance than the ground methods because of the added variables of flying the check.
Where no designated checkpoint is available, select a VOR radial that lies along an established VOR airway, then select a prominent ground point along that radial — preferably more than 20 nautical miles from the VOR ground facility — and maneuver the aircraft directly over that point at a reasonably low altitude. The maximum permissible variation between the published radial and the indicated bearing is 6 degrees.
If dual system VOR (units independent of each other except for the antenna) is installed, you may check one system against the other in place of the paragraph (b) methods. Tune both to the same VOR ground facility and compare the indicated bearings; the maximum permissible variation between the two indicated bearings is 4 degrees.
Tolerance at a Glance
| Method | Citation | Max permissible error |
|---|---|---|
| FAA/repair-station test signal (VOT) | §91.171(b)(1) | ±4° |
| Designated ground checkpoint | §91.171(b)(2) | ±4° |
| Designated airborne checkpoint | §91.171(b)(3) | ±6° |
| Airborne over a ground point on an airway | §91.171(b)(4) | ±6° |
| Dual VOR, one against the other | §91.171(c) | ±4° between the two |
Tolerances per 14 CFR §91.171(b) and (c). Ground and test-signal methods (and the dual-VOR comparison) are ±4°; the two airborne methods are ±6°.
The VOR check is one of a family of equipment-and-authorization checks an IFR aircraft must keep current. It travels alongside the RVSM altimeter and transponder inspection records and the ADS-B Out compliance and PAPR records — different intervals, different tolerances, but the same principle: the record is what proves the equipment is legal to use.
Related Aviation Compliance Guides
The Log Entry — Exactly Four Required Items
14 CFR §91.171(d) sets the record content, and it is short: each person making the VOR operational check (under paragraph (b) or (c)) must enter the date, the place, the bearing error, and sign the aircraft log or other record. That is the whole required entry — four items.
The date the operational check was performed — the anchor for the 30-day window.
Where the check was made — the VOT or checkpoint location, or the ground point used.
The error observed, against the applicable ±4° or ±6° limit for the method used.
The signature of the person who made the check — the pilot or other person, per §91.171(d).
A pilot can perform and sign the check — this is not a maintenance entry
Section 91.171(d) refers to "each person making the VOR operational check" — it does not require a certificated mechanic or repair station to run the check. A pilot may legitimately perform the operational check and make the entry. The repair-station role appears only in the (b)(1) test-signal method, where the repair station must certify the bearing it transmitted and the date of transmission. This is a meaningful contrast with airworthiness inspections, which generally require a mechanic, IA, or repair station — see the §43.9 maintenance record entry requirements for what a true maintenance entry must contain.
Record more than the minimum — but never less
The four items are the floor. Operators commonly also note the method used (VOT, ground, airborne, dual), the VOT or checkpoint identifier, the frequency, and the specific radial — all of which make the entry self-explanatory to an inspector and easier to defend a year later. That extra context is good practice and is not prohibited. What is fatal is dropping below the four required items — an entry missing the place, the bearing error, or the signature is a defective record even if the check itself was valid.
Where the entry lives matters too. The VOR check goes in "the aircraft log or other record" — it does not have to be the airframe maintenance log, and because it is not a §91.417 retention item, operators often keep a dedicated VOR-check log so the last several checks are instantly producible. For how the operational records of a charter operator are organized for inspection, see what records a Part 135 operator must keep.
Record Discipline — What an Inspector Actually Looks For
The 30-day check is only as good as the record that proves it. Because it comes due so frequently, the VOR check is one of the most common places an otherwise well-run aircraft develops a paperwork gap. Here is what a clean record set looks like — and the specific ways it fails.
Complete Record Set
- An entry within the preceding 30 days, with the date clearly shown
- The place of the check (VOT, ground/airborne checkpoint, or ground point used)
- The bearing error, evaluated against the correct ±4° or ±6° limit for the method
- The signature of the person who made the check
- (Good practice) the method, the VOT/checkpoint ID, frequency, and radial
- For the repair-station test-signal method, the station's certification of the transmitted bearing and date
How These Records Fail
- The newest check is more than 30 days old before an IFR departure
- Applying the ±6° airborne tolerance to a ground check (or vice versa)
- An entry missing the place, the bearing error, or the signature
- Treating it as a maintenance entry and burying it where it can't be found fast
- No record at all — an inspector treats a missing entry as a check never done
- Counting 30 days from the wrong date, so the window quietly lapses mid-month
FileFlo as the VOR-Check & Equipment-Records Layer
FileFlo is a compliance document intelligence platform — a read-only proof layer that sits alongside your flight and maintenance stack and completes it. It does not perform VOR operational checks, fly or dispatch the aircraft, or run a maintenance-tracking, flight-operations, or safety management system. What it does is make the records that prove these checks instantly producible.
- Classifies each uploaded VOR check entry against §91.171 and separates it from the airframe maintenance logs it is not part of
- Reads the check date and tracks the rolling 30-day window, surfacing an alert before the next IFR departure or a ramp check
- Flags an entry that is missing one of the four required items — date, place, bearing error, or signature — so a defective record is caught early
- Keeps the VOR check alongside the other equipment-and-authorization records (RVSM, ADS-B, transponder) in one indexed place
- Generates an inspector-format records view on demand, organized by requirement and due date
FileFlo classifies 600+ compliance document types and manages records across Part 91, Part 135, and Part 145 operators in a single platform. Pricing: Starter $89/mo, Professional $299/mo. 5-day free trial, no credit card required. FileFlo keeps the documents that prove compliance audit-ready — it does not provide or run a safety management system (SMS), dispatch system, or flight operations system.
Who Carries the VOR Check — and Where It Lives by Operator
Section 91.171 is a general Part 91 operating rule, so it reaches any civil aircraft flown IFR using VOR — but how it is satisfied and who is accountable shifts by operation. The trigger is always the same (IFR using VOR); the compliance path and the record location differ.
Who is responsible
Pilot / owner-operator
Usually the 30-day operational-check path, with the pilot performing and signing. The most exposed to a silently lapsed window because the check is so frequent.
Who is responsible
Pilot and/or maintenance program
May be the 30-day check or folded into an approved procedure, depending on the operator. The records must still be producible on demand for a surveillance review.
Who is responsible
Maintenance organization
The Path 1 approved-procedure route: the VOR-check obligation lives in the maintenance/inspection program, and the program records are the evidence.
The VOR check is one recurring obligation among many that an inspector cross-checks against the aircraft and pilot records. It sits beside the Part 91 §409 annual inspection requirements, airworthiness directive compliance records, and — on the pilot side — the distinct currency rules covered in pilot logbook versus operator records under §61.51. For how all of this is examined together, see how to prepare for a Part 135 FAA surveillance audit, and the Part 91 aircraft records requirements for the full records picture.
Frequently Asked Questions
How often must a VOR receiver be checked for IFR operations under 14 CFR §91.171?
Within the preceding 30 days. 14 CFR §91.171(a) prohibits operating a civil aircraft under IFR using VOR unless the VOR equipment is either maintained, checked, and inspected under an approved procedure, or has been operationally checked within the preceding 30 days and found to be within the limits of the permissible indicated bearing error. The 30-day window is counted from the date of the check, not by calendar month — a check on June 13 is good through July 13. There is no logged-time component; it is purely a 30-day operational-check window for VOR equipment used under IFR.
What are the acceptable VOR check methods and their bearing-error tolerances?
Section 91.171(b) and (c) list the accepted methods. Using an FAA-operated or approved test signal (a VOT) or a test signal radiated by a certificated repair station, the maximum permissible bearing error is plus or minus 4 degrees. Using a designated VOR system checkpoint on the airport surface, the limit is also plus or minus 4 degrees. Using a designated airborne checkpoint, the limit is plus or minus 6 degrees. Flying over a selected prominent ground point along an established VOR airway radial (preferably more than 20 nautical miles from the VOR ground facility) at a reasonably low altitude, the maximum permissible variation between the published radial and the indicated bearing is 6 degrees. For a dual independent VOR system, §91.171(c) lets you check one system against the other; the maximum permissible variation between the two indicated bearings is 4 degrees.
What exactly must the VOR check log entry contain?
Four items. Under 14 CFR §91.171(d), each person making the VOR operational check must enter the date, the place, the bearing error, and sign the aircraft log or other record. That is the complete required content: date, place, bearing error, and signature. Many operators record more — the method used, the VOT or checkpoint identifier, the frequency, the radial — and that extra detail is good practice, but the rule itself requires those four items. If a repair station radiated the test signal, the repair station must certify the bearing it transmitted for the check and the date of transmission.
Who is allowed to perform and sign the VOR check?
The pilot or another person may perform the operational check; §91.171 does not require a certificated mechanic or repair station to run the check itself. Section 91.171(d) simply says the person making the check enters the four items and signs. This is different from most airworthiness inspections — a VOR operational check is something a pilot can legitimately perform and log before an IFR flight. The one exception in the rule is the repair-station test-signal method: when a certificated repair station radiates the test signal, that repair station must certify the bearing transmitted and the date of transmission.
Is the VOR check a maintenance record under §43.9 or §91.417?
No. The VOR operational check under §91.171 is its own record category, kept in the aircraft log or other record, and it is not part of the maintenance-record retention scheme of §91.417 or the maintenance-entry rule of §43.9. Section 91.171(d) sets its own minimal content — date, place, bearing error, and signature — and §91.171 is not listed among the records §91.417 requires an owner or operator to keep. A pilot-performed VOR check is not a maintenance entry; it is an operational-check entry. Keep it where you can produce the last 30 days of checks, but do not conflate it with the airframe maintenance logs.
Does a GPS or RNAV-equipped aircraft still need the §91.171 VOR check?
If you intend to operate under IFR using VOR, yes — §91.171(a) is triggered by IFR operation using VOR, so an installed and used VOR receiver must have a check within the preceding 30 days regardless of what other navigation equipment is aboard. If the aircraft is flown IFR purely on a different, properly authorized navigation source and the VOR is not used for the IFR operation, the §91.171 trigger turns on the use of VOR. Because this is a fact-specific airworthiness and operational determination, confirm with your avionics shop and FSDO how your equipment, operations specifications, and approvals interact before relying on a non-VOR navigation source to skip the check.
What happens at a ramp check if the last VOR check is older than 30 days?
An FAA Aviation Safety Inspector can ask to see the VOR check record. If the most recent operational check is outside the preceding 30 days — or if there is no record at all — the aircraft is not eligible to operate under IFR using VOR until a fresh check is performed and logged with the four required items. The inspector cannot distinguish "the check was done but never written down" from "the check was never done," so a missing entry is treated the same as a lapsed one. The fix is fast for a pilot-performed method, but the record is what proves it, and the record is what an inspector or auditor actually examines.
Does FileFlo perform VOR checks or fly the aircraft?
No. FileFlo is a compliance document intelligence platform — a read-only proof layer. It does not perform VOR operational checks, fly or dispatch the aircraft, or run a maintenance-tracking, flight-operations, or safety management system. What FileFlo does is classify and index the VOR check entries you upload, read the check date, and track the rolling 30-day window so a lapsed or missing VOR check surfaces as an alert before an IFR departure or a ramp check — instead of being discovered by an inspector. The check itself is performed and signed by the pilot or other person making it, per §91.171(d).
Never let the 30-day VOR check lapse under you
FileFlo classifies your §91.171 VOR check entries, reads each check date, tracks the rolling 30-day window, flags any entry missing one of the four required items, and generates a complete inspector-format records view on demand. Starter plan $89/mo. Professional $299/mo. 5-day free trial — no credit card required.
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Written by Chad Griffith, Founder & CEO of FileFlo — compliance document intelligence. Reviewed June 13, 2026. FileFlo is a compliance document intelligence platform, not legal counsel, an A&P, or a repair station. Verify the VOR check window, accepted methods, tolerances, and who-may-sign rules against the current regulation and with your avionics shop and FSDO.