VOR receiver check

A question to all IFR pilots concerning the FAR 91.171 VOR-Check:
Is a check that uses a GPS signal from the GNS430 to check the VOR-accuracy a legal substitute for the types of checks specified in the FAR?
At my hometown airport, there is no VOT or designated surface-checkpoint etc. (outside U.S.!), so what I can do is check the bearing from a VOR that’s 10 miles away using the GPS, then tune the VOR and set the GPS bearing indication on the OBS and check deviation. This is probably a very accurate check, but probably not approved by 91.171. Does anyone know for sure?

One more question on IFR-curency: At which moment exactly do I need a current database on my GNS430 to be legal for IFR? I mean, GPS is not generally required for IFR at all. Do I need the current database as soon as I enter SR20/G in the flightplan? Or, as soon as I fly an NDB approach using the GNS430?
BTW, do you “C”-version owners you keep both of your GNS430s current or just one?

Please advise

Good morning Phil,
very interesting questions you are raising on a very early Sunday morning. Here are my 2 cents:

I have a SR20 C, N747TG. I update both GNS430s religeously every month. Jeppesen offers a special price for dual installations, so this is a no-brainer. I use the download version and write my own datacards, a very easy operation.

Concerning the /G: According to ICAO and AIM, the /G adds “Transponder, Mode C and GNSS with enroute AND terminal capability”. So, the clear answer is that your data card MUST be current if you file “G” because the terminal part is included. If your GNS430 is not current, you put in “S/C” only, meaning that your aircraft is equipped for what is needed enroute (this would exclude all NDB, NDB-DME, and VOR-DME approaches, and not allow for ILS approaches if there is a compulsory DME). To keep it simple and stupid: update your data base to avoid all these restrictions and traps.

Concerning the VOR 30 day rule, you’ve made a good point. If you have 2 VORs (like in the C model), you compare VOR1 against 2 and keep it within 4 degrees. With 1 VOR only, you need to use VOR checkpoints as indicated in the A/FD, either on the ground, or airborne. There should be one or 2 in your area. Your idea of checking against the GPS is excellent but not yet legal, to my knowledge.

Have a wonderfull Cirrus day,

Timm Preusser CFII

Also no VOT in my area (EHLE), and I hope to afford the “A”-model (1 GNS430), I’m for now VFR-only (would like to do the IR after getting the Cirrus with a Cirrious CFII) but any idea’s how I can perform the VOR test ?

Also, any news about the Garmin GTX330 ModeS transponder update in the SR2X (required in Europe for IFR in 2003 and for VFR in 2005) ?

Jaap #683

Thank you for your detailed information Tim. But don’t worrry, due to the timeshift, it was just before noon when I posted! I don’t usually surf the internet at 4:30 local…

Best regards,

I agree with Timm’s response but since CFIIs like to quibble and split hairs, here goes. You do not need a current database in the Garmins to use it for either enroute or terminal operations. You DO need it to be current to fly an approach. For any operation OTHER THAN FLYING AN APPROACH you can have an expired database provided you “verify” all data for correctness. I presume this means that you would have to compare the lat/long of a fix in your out of date database with the known coordinates of the fix etc. As a practical matter, if you’re going to fly IFR, have a current database. I agree with Timm that keeping both current is not a big deal and it’s certainly good operating practice.
The VOR receiver check must be performed as specified in FAR 91.171. I love to point out to my students that you could check VOR receiver #1 against #2 and if #1 is off by 50 degrees and #2 off by 54 degrees then they’re within 4 degrees of each other and pass the check. Your idea of comparing the VOR to GPS is clearly more accurate but it’s not legal. Go figure. Another example of the “bureaucratic mind” being the mother of all oxymorons.
By the way, if you do your VOR check with #1 vs #2 and plan to really use the VOR system then it’s a good idea to be sure that the bearings you see on the indicators are close to what you know they should be given your location and the location of the VOR you’re using for the check.
For a reference of types of GPS operations (enroute, terminal and approach) see the AIM
Jerry Seckler CFII

Thanx Jerry. I think I got the point about the GPS database and as Jim said, almost every instrument approach (in an SR2x) must be done at least by also using GPS except those plain ILSs. It seems there is no way around a current database (or even two).
Doing the VOR check however, remains a bit of a struggle outside the U.S. because the FAA of course doesn’t make any provisions for VOR checks outside the U.S., although there occasionally are VOTs here, too, but none on my homebase.
I think what I’ll do in the future is do the GPS vs. VOR check for myself and then do the dual cross check for the record.


I presume you’re going to register your aircraft as an “N” aircraft and are therefore subject to FAA rules. To see how you can do a VOR check with one VOR get a copy of FAR 91.171. Basically you can check a single VOR in the following ways:

  1. a VOT, 2. a signal radiated by an “approved authority” (such as a certified avionics shop), 3. a point on the airport designated by the appropriate authority as a VOR check point 4. in flight by selecting a VOR radial that lies along the centerline of an established VOR airway. Then you select a prominent ground point along that airway preferably at least 20 miles from the VOR. You maneuver the airplane directly over that point and note the VOR bearing indicated at that point. As long as it is within 6 degrees of the published radial making up the airway you’re OK.
    Of course no matter how you accomplish the test you have to log it. Paperwork is everything.
    Jerry Seckler