VOR Checks

Per 14 CFR Part 91.171, VOR equipment must be checked in the preceding 30 days if it's to be used for navigation under IFR. What this means is that if are not intending on using it for navigation, you technically don't need to do a check. Since VOR is a great backup form of navigation for all of you children of the magenta line, it's best to keep your VOR checks up to date.

Paragraph (a)(2) is what pertains to us. There are four (4) ways of executing a VOR check. Here is a table with summary and tolerances. Keep reading for a detailed description of each.

Type	Summary	Tolerance
Dual VOR	Compare two CDIs	+/- 4
VOR Checkpoint	Tune to specified radial	+/- 4
VOT	R-360 FROM / R-180 TO	+/- 4
Airborne Check	Tune to known radial	+/- 6

Dual VOR Check

Max permissible error: +/- 4 deg

This method is in my opinion the easiest, assuming you have at least TWO navigation radios (so NAV 1 and NAV 2) and either two CDIs or two bearing pointers. Here is the procedure:

For two CDIs: A. Tune both NAV 1 and NAV 2 to the same VOR

B. Center the needles with a two indication on both CDIs (i.e., home the VOR)

C. Compare the difference between the two.

D. The check is satisfactory if there is a delta of 4 degrees or less between the two needles.

With bearing pointers (i.e., the easy way):

A. Tune both NAV 1 and NAV 2 on the same VOR

B. Engage bearing pointer 1 and bearing pointer 2 (tuned to each NAV, so bearing pointer 1 is tuned with one NAV radio and the second is tuned to the other NAV radio)

C. The check is satisfactory if there is a delta of 4 degrees or less between the two needles.

VOR Check Point

Max permissible error: +/- 4 deg

VORs are designed to be used in the air. For this reason, there aren't many places on the ground where you can receive a strong enough signal to test your instruments. But that doesn't mean that there aren't! Many airports across the country will have VOR check points located on the ground. They are usually found on taxiways and are marked by horizontal paint on the asphalt and signs with the corresponding VOR frequency and radial.

A great example is found at Lakeland International Airport (KLAL), holding short of runway 10 (full length). In the image below, the circle with the arrow on the ground marks a VOR checkpoint. That arrow usually points at a sign in the grass, where relevant information is provided (see the second image).

Yeah, the image was taken at night because that's when I was there. The sign indicates that at the specified location, you can verify your VOR equipment using the LAL VORTAC on R-103 or R-283.

The iconography is not always the same, but it's pretty obvious. Here's another example from Charleston International Airport (KCHS) on taxiway E.

VOR Test Facility (VOT)

Max permissible error: +/- 4 deg

A VOT is an approved, FAA-operated test signal radiated by a certified, rated radio repair station. This is a test VOR to which pilots can tune and verify correct indications. The VOT check is intended to be used on the ground only. This is because FAA Order 6050.32B, which talks about spectrum maangemange regulations, says that the VOT frequency is not protected in the air. That being said, the AIM (1-1-4) allows pilots to perform airborne tests if allowed in the appropriate chart supplement. If you want to be safe, just do the test on the ground, "as its intended to be done".

The point of the VOT is to create a fictitious R-360, independent of your position. When you tune to a VOT, your needles must position you on R-360. That means that your needles must be centered on R-360 indicating a FROM indication. Else, you could also tune R-180 but with a TO indication. So here is teh easy procedure:

A. Tune each NAV radio to the VOT frequency.

B. Dial R-360.

C. Verify you have a FROM indication.

D. The check is satisfactory if there is a delta of 4 degrees or less  from R-360.

E. Dial R-180.

F. Verify you have a TO indication.

G. The check is satisfactory if there is a delta of 4 degrees or less  from R-180.

You can find information on local VOT frequencies on your Electronic Flight Bag (EFB). I'll use the example of Garmin Pilot using the frequency page (left) and the chart supplement (right):

Garmin Pilot Airport FREQ Page	Chart Supplement

Airborne VOR Check

Max permissible error: +/- 6 deg

This is the easiest and most common VOR equipment check. The idea is to position yourself over a prominent ground point conveniently located on an airway. You can verify the radial that defines the airway and perform your check. Ideally, the position should be further than 20 NM away.

An example is provided below north of Savannah, GA (KSAV). On V185 northwest bound, there is the city of Springfield with a bunch of obstacles.

Based on the IFR chart, R-341 defines V183. I should be able to tune that radial over Springfield and be right on that airway! Now, because my location precision is obviously not as great as a VOR check point or VOT, the tolerances are relaxed to 6 degrees. Here is a quick procedure:

A. Tune each NAV radio to the VOR frequency.

B. Dial R-341 (FROM) or the reciprocal, R-161 (TO) depending on your direction of travel.

C. Verify your CDI deflection is no more than 4 degrees off.

Personally, I am not a fan of this particular test because magnetic declination may offset airways a little bit, giving you offsets that are not true.