>[!info]- § 91.171 VOR equipment check for IFR operations. > No person may operate a civil aircraft under IFR using the VOR system of radio navigation unless the VOR equipment of that aircraft— > > Is maintained, checked, and inspected under an approved procedure; or > > > 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)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(b)) or [(c)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(c)) of this section. > > Except as provided in [paragraph (c)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(c)) of this section, each person conducting a VOR check under [paragraph (a)(2)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(a)(2)) of this section shall— > > 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 > > > 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); > > > 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 > > > If no check signal or point is available, while in flight— > > > 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; and > > > > > 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). > > 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)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(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. > > Each person making the VOR operational check, as specified in [paragraph (b)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(b)) or [(c)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(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)](https://www.ecfr.gov/current/title-14/section-91.171#p-91.171(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. VOR Inspections must be completed within the preceding 30 days for *IFR flight* and this inspection can be completed by a pilot # Methods of Completing Inspection ## VOT Signal 1. Tune to the VOT signal 2. Set course to 0 degrees - The CDI should center 3. A from indication should be displayed 4. Set course to 180 degrees 5. A to indication should be displayed *The Maximum Bearing Error is* $\pm 4 \degree$ ## VOR Checkpoint - VOR checkpoints are typically located near taxiways, ramps, or runup areas - A sign will indicate where one is located - Simply follow the instructions on the sign *The Maximum Bearing Error is* $\pm 4 \degree$ ## Dual VOR Check This is typically the easiest and most convenient check to do if you have an airplane equipped with more than 1 VOR receiver 1. Tune both VORs to the same frequency 2. Center both needles with a to indication 3. Note the bearings from each receiver *The Maximum Differential between the 2 VORs is* $4 \degree$ ## Airborne VOR Check 1. Select a VOR radial that is on a VOR airway 2. Select a prominent ground reference - preferably more than 20 NM from the station 3. Note the VOR bearing indicated by the receiver when over the ground point *The Maximum Bearing Error is* $\pm 6 \degree$