John Peltier

When was the last time you checked your VOR receiver? As an IFR pilot, how often are you required to do this test? What about as a VFR pilot? Are you required to check your VOR receiver?

The answer for VFR pilots is, well, no you’re not required to check your VOR receiver. That doesn’t mean that it’s not a good idea.

And for IFR pilots, how often do the Federal Aviation Regulations say you must check your receiver when using it for instrument flying?

According to FAR 91.171, you may not conduct an IFR flight using VORs for navigation unless your VOR system has been checked within the preceding 30 days and found to be in limits. The check must also be logged in the aircraft records.

Fortunately, these are checks that pilots can accomplish on their own, and in many different ways.

The FAA allows pilots a handful of different methods for checking VOR receivers. There’s an easy acronym to remember about these tests, including tolerances – do you know it?

The acronym most taught to IFR students is VODGA. This stands for VOT, Ownship, Dual, Ground, Air. Let’s take a closer look at the steps to check your VOR receiver using this acronym.

VOT

The VOR Test Facility (VOT) is the most accurate and is the preference to check your VOR receiver. Not all airports have a VOT. You can discover which airports do have a test facility in Section 4 of the FAA Chart Supplement (formerly known as the Airport Facility Directory [AFD]). The supplement indicates which airports have the test equipment, which frequency to use, and any other notes specific to that location.

Steps to using the VOT:

  1. Ensure you are situated on the airport in an appropriate area – the parking apron, taxiway, or end of runway. The Supplement will make note of which areas on the airport will not work.
  2. Tune to the appropriate frequency annotated in the Supplement.
  3. Turn up the volume to identify the station, which is indicated by a series of dots or one continuous tone.
  4. Twist the OBS to center the needle. The TO/FROM flag should indicate TO with 180 degrees (+/- 4) selected. Remember: Cessna 182. One-eighty two, or 180-TO. It should show FROM with 360 selected.
  5. The tolerance must be within four degrees, i.e. the needle must be centered when the OBS is from 176 to 184 degrees or 356 to 004 degrees.

In the absence of a VOT, you may use other checkpoints designated in the Supplement. These are the ownship tests, and they may be conducted in the air or on the ground.

Ownship

Checking your VOR receiver may be done at either a designated location on certain airfields or over specific geographic locations while airborne. These locations, frequencies, and notations may also be found in Section 4 of the FAA Chart Supplement. The Supplement will provide the name of the VOR and/or airport facility, the frequency, and whether or not it is a ground or airborne checkpoint. If it’s an airborne checkpoint, minimum altitudes will also normally be listed. If it’s a ground checkpoint, the location on the airfield to perform the test will be listed.

Ground checks are preferred over air checks because it’s easier to position your aircraft to a more precise location on the ground.

Steps to doing an ownship location VOR receiver check:

  1. Tune to the appropriate frequency annotated in the supplement.
  2. Identify the station by turning up the volume and ensure the Morse code or voice identifier is correct.
  3. Twist the OBS knob to the azimuth listed in the Supplement.
  4. Position your aircraft at the appropriate location annotated in the Supplement, either on the ground or over a geographic location in the air, ensuring you’re at an appropriate altitude if airborne.
  5. If the needle is not centered, twist the OBS until it centers up.
  6. The tolerance must be within four degrees for ground checkpoints or six degrees for air checkpoints. So if an airborne checkpoint azimuth is listed as being 177 degrees, the OBS must be centered in a range from 171 to 183 degrees.

You may also make your own airborne check by looking at the charts and picking a significant geographic landmark under a VOR airway. Fly over the landmark and note the azimuth that your aircraft VOR receiver indicates. It should be within 6 degrees of the annotated airway azimuth.

The FAA allows for one more method of checking a VOR receiver, and you may do this if you have two separate receivers in your aircraft (they can share an antenna).

Dual Receiver Check

A dual receiver check is valid if you have two separate receiver units in your aircraft. They can have a common antenna but the actual receivers must be separate. These checks can be done on the ground or airborne.

Steps to conducting a dual receiver VOR check:

  1. Tune both receivers to a nearby VOR station.
  2. Identify the station in both receivers by turning up the volume and verifying the Morse code or voice identifier.
  3. Compare the OBS settings for both receivers with the needle centered. They must be within four degrees of each other.
Ground / Air

The final pieces of the VODGA acronym, GA, is to remind you that there are different tolerances for ground checks and air checks. It should make sense that ground checks are more accurate, and thus have a lower tolerance for error. All tolerances are 4 degrees, including a dual check in the air. The only exception is the ownship airborne check, which has a tolerance of 6 degrees.

Logging the VOR Receiver Check

This may be the most neglected part of the VOR checks, and if the check is not logged you are in violation of the FARs. Doing the actual checks is important! But so is logging them.

Logging the check is easy. It doesn’t even have to be in official aircraft maintenance logs, it just needs to be with the aircraft and available for inspection. A simple spreadsheet will suffice.

The log must contain the date, location, bearing error, and signature of the pilot conducting the check.

Summing Up the VOR Receiver Check

If you’re an IFR pilot using VORs for navigation, you must check your VOR receiver within 30 days preceding an IFR flight, and log the check.

You may check two receivers against each other if your aircraft has two separate units. This will be the easiest if you have two units. Tolerance is 4 degrees.

You can also check your receiver while on the ground at certain airports using a dedicated VOR test facility or a designated VOR ground checkpoint, both found in the FAA Chart Supplement. Tolerance is 4 degrees.

In the absence of any other way to check your VOR, you may conduct a check airborne. The tolerance is 6 degrees.

The checks must be logged with the date, location, bearing error, and signature.

These regulations are found in FAR 91.171. More information can be found in AIM 1-1-4. But most importantly, don’t forget to keep current with these checks, and log them.

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Featured Image: Ryan Blanding

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