Which is the maximum tolerance for the VOR indication when the CDI is centered and the aircraft is directly over the airborne checkpoint?

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(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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You need to make sure that your IFR equipment is checked and within specific tolerances before you take off. Here's what you need to know before your next flight...

VOR Checks

If you're planning to use your VOR receiver, the receiver must be checked within the preceding 30 days of the IFR flight (14 CFR 91.171). This goes for every IFR certified airplane, regardless of size. If there's something wrong with your navigation receiver, it's better to know early on before you find yourself flying miles off-course.

Here are a few ways you can get this required check done:

• VOT Signal: With a VOT, you can check the VOR accuracy from your plane before takeoff. So what is a VOT? It's an approved VOR test signal, and it's located on an airport. Not all airports have VOTs, so you'll need to check the chart supplement to see if your airport has one. If your airport does have a VOT, here's what to do:
  • Tune your VOR to the VOT signal.
  • Set the course selector to 0 degrees, and the track indicator should be centered.
  • The TO-FROM indicator should read FROM.
  • Next, set the course selector to 180 degrees
  • The TO-FROM indicator should read TO, and the track bar should then be centered.
  • The maximum indicated bearing error is plus or minus 4 degrees.


• VOR Checkpoint: Many airports have VOR checkpoint signs that are located near a taxiway, ramp or runup area. These signs indicate the exact point on the airport where there is sufficient signal strength from a VOR to check the aircraft's VOR receiver against the radial designated on the sign. To use a VOR checkpoint, simply follow the instructions on the sign.
  • The maximum indicated bearing error is plus or minus 4 degrees.


• Dual VOR Check: This is often times the easiest check to accomplish, as long as you have 2 VOR receivers. To check dual VOR receivers against one another:
  • Tune both NAV radios to the same VOR facility.
  • Center the needles of each VOR receiver with a "TO" indication.
  • Note the indicated bearings to the station from each receiver.
  • The maximum indicated bearing error is 4 degrees.


• Airborne VOR Check: VOR equipment can also be checked for accuracy in flight. To accomplish an airborne VOR check:
  • Select a VOR radial that lies along the centerline of an established VOR airway.
  • 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.
  • Note the VOR bearing indicated by the receiver when over the ground point.
  • The maximum indicated bearing error is plus or minus 6 degrees.

Recording Your VOR Check

Once your check is done, you need to record it. Here's what the FARs require:

• 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.

RNAV Accuracy

GPS and RNAV make IFR flying a whole lot easier than traditional VOR navigation. There are some checks you need to perform prior to takeoff to ensure your data is accurate for GPS too:

• System Initialization: As you power up your avionics, check to make sure the navigation database is updated and that the aircraft's current position is accurate.
• Flight Plan Check: Review your programmed flight plan in comparison to charts and your IFR clearance. Ensure that nothing is missing from the navigation database.
• RAIM Prediction: If you don't have a WAAS receiver, and you're planning to fly on an RNAV route or us an RNAV/GPS approach, you should complete a RAIM prediction on your equipment.

Everyone has found some type of equipment or database problem on an airplane. And obviously, it's better to find these problems on the ground than in the clouds under IFR. Do a thorough preflight check, and you'll be good to go in the air.

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