What is acceptable airborne VOR accuracy (+ or -)?

(a) No person may operate a civil aircraft under IFR using the VOR system of radio navigation unless the VOR equipment of that aircraft -

(1) Is maintained, checked, and inspected under an approved procedure; or

(2) Has been operationally checked within the preceding 30 days, and was found to be within the limits of the permissible indicated bearing error set forth in paragraph (b) or (c) of this section.

(b) Except as provided in paragraph (c) of this section, each person conducting a VOR check under paragraph (a)(2) of this section shall -

(1) Use, at the airport of intended departure, an FAA-operated or approved test signal or a test signal radiated by a certificated and appropriately rated radio repair station or, outside the United States, a test signal operated or approved by an appropriate authority to check the VOR equipment (the maximum permissible indicated bearing error is plus or minus 4 degrees); or

(2) Use, at the airport of intended departure, a point on the airport surface designated as a VOR system checkpoint by the Administrator, or, outside the United States, by an appropriate authority (the maximum permissible bearing error is plus or minus 4 degrees);

(3) If neither a test signal nor a designated checkpoint on the surface is available, use an airborne checkpoint designated by the Administrator or, outside the United States, by an appropriate authority (the maximum permissible bearing error is plus or minus 6 degrees); or

(4) If no check signal or point is available, while in flight -

(i) Select a VOR radial that lies along the centerline of an established VOR airway;

(ii) Select a prominent ground point along the selected radial preferably more than 20 nautical miles from the VOR ground facility and maneuver the aircraft directly over the point at a reasonably low altitude; and

(iii) Note the VOR bearing indicated by the receiver when over the ground point (the maximum permissible variation between the published radial and the indicated bearing is 6 degrees).

(c) If dual system VOR (units independent of each other except for the antenna) is installed in the aircraft, the person checking the equipment may check one system against the other in place of the check procedures specified in paragraph (b) of this section. Both systems shall be tuned to the same VOR ground facility and note the indicated bearings to that station. The maximum permissible variation between the two indicated bearings is 4 degrees.

(d) Each person making the VOR operational check, as specified in paragraph (b) or (c) of this section, shall enter the date, place, bearing error, and sign the aircraft log or other record. In addition, if a test signal radiated by a repair station, as specified in paragraph (b)(1) of this section, is used, an entry must be made in the aircraft log or other record by the repair station certificate holder or the certificate holder's representative certifying to the bearing transmitted by the repair station for the check and the date of transmission.

(Approved by the Office of Management and Budget under control number 2120-0005)

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Although not required for VFR flight, I recommend you observe the thirty day VOR check that we must do for IFR flight, especially if you ever intend to get your instrument rating. Knowing how accurate your VOR receivers are, and/or which is the most (or least) accurate will serve you well, even during VFR navigation.

FIRST METHOD

As pilots, we have several ways to check our VOR accuracy. The first is to use a VOR test facility or VOT. Most of these must be used on the ground, although there are a few in the flat lands of the Midwest and the South that can be used while airborne. You'll find VOT locations and frequencies in the green chart supplement

Also check the reciprocal reading of the VOT signal by noting a similar needle swing in the opposite direction and a TO flag when you dial the OBS to 180. An easy way to

SECOND METHOD / ON THE GROUND

Another way we can check VOR accuracy is using a certified checkpoint either on the ground or in the air, as specified in the chart supplement. For example, there is a ground-based check

SECOND METHOD / IN THE AIR

Sometimes these checkpoints can be airborne. An example of that

THIRD METHOD

Yet another way we can check our VORs is to select a radial along a Victor airway. Find a prominent ground point more than 20-miles from the VOR and maneuver the aircraft directly over the

FOURTH METHOD (THE EASIEST WAY)

A final way for a pilot to check VOR accuracy is to compare one against the other. This is perhaps the easiest method. Tune both

WRITE IT DOWN

After you've done your check, it must be recorded, but not in the aircraft maintenance records or logbooks. Those generally won't be in the airplane anyway. Just log it on a basic form or in a flight log that is stored in the airplane, using the PADS format:

P - The place you made your accuracy check.

A - The amount of error, plus or minus, on each VOR

D - The date you conducted the test.

S - Your signature.

And of course, if one (or both) of your VORs does not conform to the maximum allowable error ---- 4° on the ground or 6° in the air ---- IFR flight should not be attempted without first correcting the source of the error.

ONE MORE WAY

Another way to verify VOR accuracy is to have a repair facility, rather than you, the pilot, perform the check. If an avionics shop checks your VORs, especially after installation or repair. --- they , not you --- will make an entry verifying VOR accuracy in the aircraft log or other record.

While you don't have to memorize everything I've covered in this article, you should generally be familiar with the variety of ways to check your VORs accuracy, and how to record those checks. At the very least, look in the FARs --- 91.171 (click here) --- to refresh your memory of acceptable methods of checking VOR accuracy...

© Garry Wing 2016