Very High Frequency (VHF) omni-directional range - abbreviated aviation term VOR - is a short-range radio navigation whose signals sweep 108.0-117.95 MHz and give 360 azimuth information as radials of magnetic heading. A VOR Check confirms that the aircraft's VOR receiver is functioning within acceptable tolerances by comparing the difference between variable and reference phases to show bearing from the station. The FAA Approved VOR Test Facility (VOT) is a ground-based transmitter on an airport that transmits a test signal and, together with published VOR checkpoints, provides users a convenient means for this verification procedure.
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What is a VOR test in aviation?
A VOR test in aviation is a procedure used to verify that a VOR receiver accurately determines aircraft bearing from the station by comparing the difference between the variable and reference phases. The test relies on a VOR test signal, which is an FAA operated or approved test signal that defines a radial with a to/from indication. This signal is radiated by a certificated and appropriately rated radio repair station or provided by an appropriate authority outside the United States. The plane checks VOR accuracy before takeoff at the airport of intended departure or at a point designated as a VOR system checkpoint by the Administrator.
VOR checks guarantee navigation accuracy by using either a test signal, an airborne checkpoint, or a ground checkpoint. A ground checkpoint is a point on the airport surface designated as a VOR system checkpoint by the Administrator, and the maximum permissible indicated bearing error for this check is plus or minus 4 degrees. An airborne checkpoint, designated by the Administrator, allows a maximum indicated bearing error of plus or minus 6 degrees. When using an FAA operated or approved test signal, the maximum permissible indicated bearing error is also plus or minus 4 degrees.
What is a VOT VOR in aviation?
A VOT is an approved VOR test signal located on an airport, and users can check the VOR accuracy from their plane before takeoff by tuning their VOR to the VOT signal. VOT is a ground VOR receiver check method. VOT is a special ground-based transmitter located at certain airports, is listed in the Airport Facilities Directory, and emits a radial beam on the 360 degree radial.
The VOT provides users a convenient means to determine the operational status and accuracy of a VOR receiver while on the ground. VOT transmits a test signal and a VOR tuned to VOT signal shows CDI centered at 360 degrees. VOT check tolerance is plus or minus 4 degrees; if your CDI reads 356 degrees there is an error of 4 degrees.
Airborne use is permitted only where authorized in the Chart Supplement or appropriate supplement; tolerance airborne VOT is 6 degrees. VOT is the most accurate and preferred means to check your VOR receiver.
How to test VOR equipment on an aircraft?
To test VOR equipment on an aircraft, follow the instructions given below.
- Perform VOR equipment check using a point on the airport surface designated as a VOR system checkpoint
- Perform VOR receiver check by using a VOT signal or a radiated test signal from an appropriately rated radio repair station
- Perform VOR receiver check by using a designated VOR ground checkpoint found in the FAA Chart Supplement
- Conduct airborne check by maneuvering the aircraft directly over the point at a reasonably low altitude
- Select a prominent ground point along the selected radial preferably more than 20 nautical miles from the VOR ground facility while in flight
- With the CDI centered, read 0 with the to/from indication showing "from"
- Use at the airport of intended departure a point on the airport surface designated as a VOR system checkpoint
- Set both OBS knobs to same radial
- With CDI centered, omni-bearing selector should read 0 degrees with TO/FROM indication showing from
- Turn both systems to the same VOR ground facility for VOR receiver comparison
- Maneuver the aircraft directly over the point at a reasonably low altitude while in flight
- Set both OBS knobs to the same radial for a dual system check
- Use FAA-operated test signal as an approved test signal
- Tune both VOR receivers to the same VOR station
- Radiate test signal by a certificated and appropriately rated radio repair station
- Compare the CDI indications
- Make arrangements with repair station to have test signal transmitted
When must an operational check of the aircraft VOR be performed?
An operational check of the aircraft VOR must be performed 30 days prior. No person shall operate a civil aircraft under IFR using the VOR system of radio navigation unless the VOR equipment has been operationally checked within the preceding 30 days (14 CFR 91.171). The 30-day VOR check requirement is found in FAA CFR 91. Operational checks of VORs must be made every 30 days for aircraft operating under Instrument Flight Rules. Some 129 units like the non WAAS Garmin 430 contain a certified VOR and ILS and must be checked operationally and the results logged under 14 CFR 91.171 when used for IFR flight.
