Very High Frequency Omnidirectional Range (VOR)

The VHF omnidirectional range (VOR) is a ground-based, short-distance navigation aid (NAVAID) which provides continuous azimuth information in the form of 360 usable radials to or from a station. It is the basis for the very high frequency (VHF) airway structure. It is also used for VOR non-precision instrument approaches.

VORs in Canada operate on assigned channels spaced at 0.05 MHz (50 kHz) increments within the frequency range 112.0 to 117.95 MHz.

The implication for users is that, in airspace serviced solely by VOR, aircraft equipped with older VOR receivers which cannot be tuned to two decimal places (e.g. 115.25 MHz) may not be able to operate under instrument flight rules (IFR). Of course, area navigation (RNAV), where approved for use, may enable operation under IFR.

Receivers with integrated distance measuring equipment (DME) (i.e. VOR/DME receivers) normally select the associated DME “Y” channel automatically, while stand- alone DME receivers display the “X” and “Y” channels separately.

VOR reception is subject to line-of-sight restrictions and range varies with aircraft altitude. Subject to shadow effect, reception at an altitude of 1,500 ft above ground level (AGL) is about 50 NM. Aircraft operating above 30,000 ft normally receive VOR at a distance of 150 NM or more.

Identification is accomplished by means of a three-letter location indicator keyed in Morse code at regular intervals.

Theoretically, an infinite number of courses (radials) are radiated from a VOR station, however, in actual practice, 360 radials are usable under optimum conditions.

The accuracy of course alignment for published VOR radials is ±3°. Unpublished radials are not required to meet a particular standard of accuracy and may be affected by siting difficulties. Any significant anomalies in published radials sent out from VOR serving an aerodrome will be published in the Canada Flight Supplement (CFS).

Where RNAV routes have not been published, VOR remains the primary NAVAID for use in Canada. It is important that the accuracy of the aircraft equipment be checked in accordance with principles of good airmanship and aviation safety.

While standard avionics maintenance practices are used for checking aircraft VOR receivers, dual VOR equipment may be checked by tuning both sets to the same VOR facility and noting the indicated bearings sent to that station. A difference greater than 4° between the aircraft’s two VOR receivers indicates that one of the aircraft’s receivers may be beyond acceptable tolerance. In such circumstances, the cause of the error should be investigated and, if necessary, corrected before the equipment is used for an IFR flight.

Aircraft VOR equipment may also be checked while airborne by flying over a landmark located on a published radial and noting the indicated radial. Equipment which varies more than ±6° from the published radial should not be used for IFR navigation.