VOR Check
If a VOR is to be used for navigation under IFR flight rules—regardless of weather conditions—it must be operationally checked within the preceding 30 days. The check can be done with any of the following six methods:
1. VOR test signal at a certificated repair station. ±4° bearing error.
2. FAA VOR test facility (VOT). ±4° bearing error.
3. Designated surface checkpoint. ±4° bearing error.
4. Airborne checkpoint. ±6° bearing error.
5. Inflight check using prominent ground point on an airway. ±6° bearing error.
6. Dual VOR check. ±4° bearing difference between VOR readings.
You must enter the date, place, bearing error, and sign the aircraft log or other record.
Notes:
1. The signal is normally 108.0 MHz and repair stations are not permitted to radiate the VOR test signal continuously. In general, this option is mostly used if there is a problem with the VOR. The bearing is selectable.
2. Listed in the back of the A/FD as “VOR Test Facilities (VOT)”, They are frequently found at larger airports. The AF/D often has a note saying that they are “unusable except in the runup area”. They transmit the 0° radial. If the OBS is set to 0° there should be a FROM indication, if the OBS is set to 180° there should be a TO indication. An RMI (Radio Magnetic Indicator) will indicate 180 degrees on any omni-bearing selector (OBS) setting.
3. Listed in the back of the A/FD as “VOR Receiver Checkpoints”. From looking at the A/FD it appears that most of the designated surface checkpoints are at airports that have a VOR on the field or nearby. The A/FD has the location on the field where the check should be made, the mileage, and the radial. There are very few that are farther than 6 nm away. Very few have designated markings on the field, instead they are at taxiway intersections, runup areas, in front of the terminal, etc.
4. Listed in the back of the A/FD as “VOR Receiver Checkpoints” under the name of the VOR. Similar to the ground checkpoints except that they also contain an altitude. Many of them are located over the approach end of the runway at TPA. Some VORs have airborne checkpoints at the approach end of several airports.
5. 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.
6. The dual-VOR check is probably the most common way to check VORs. If you have two VORs that are independent except for the antenna, then center both to the same radial and note the bearing. The difference between the bearings on the two VORs must be less than 4°.
Ways you _cannot_ check your VORs.
1. Using the Radio Aids to Navigation section for an airport in the A/FD, note the radial and distance to the listed VORs.
2. Use a sectional to determine the radial of a prominent ground point not on an airway.
3. Use your GPS to determine the radial of an airborne or ground location.
4. Perform a VOR check and then use the VOR to determine the radial of a prominent landmark or ground location.
The easiest way to log the VOR check is to keep a small notebook in the plane and make a note in it each time you make the VOR check. Since the PIC is responsible for the VOR check, if you fly several airplanes, it might be a good idea to keep a notebook with your flight bag and log the VOR checks in it for each plane.
One check you can make, that is not required, is to center the needle and note the bearing. Turn the OBS 2°. The needle should now be centered over the first dot, repeat for each dot until you are 10° from the starting point. The needle should be over the last (5th) dot.
Refer to to AIM 1-1-4. VOR Receiver Check (link) or
FAR §91.171 (link) for details.
FAA Knowledge Tests
Try your hand at answering some questions on thunderstorms from the tests.