There are 10 degrees of deflection on either side of the center disk, creating 20 degrees total indicating capability. Each dot represents a 2-degree deflection from the desired course. The direction of deflection tells the pilot where he is relative to the radial, while the dots on the instrument's face tell the pilot how many degrees he is off his course. A Left/Right needle called a course deviation indicator (CDI) shows the pilot how many degrees and in which direction from the selected radial he is flying. The VOR indicator in the cockpit features an OBS (omni bearing selector) knob that the pilot uses to select VOR radials by placing them above the course index (on top of the VOR indicator) or below the reciprocal course index (at the bottom of the VOR indicator). Many VORs also have voice capability that can identify the VOR or give the pilot weather information, including HIWAS (hazardous in-flight weather advisories), TWEBs (transcribed weather broadcasts), and instructions from flight service stations. So, with the right equipment in the cockpit, pilots can determine not only their radial relative to the VOR station but also the slant-range distance from their aircraft to the station. VOR-DME stations and vortacs both have distance measuring capabilities. So, if there's a mountain between you and the VOR, you will not receive a reliable signal even though you are within the station's range.Īll VORs operate within the 108.0 to 117.95 MHz frequency band. Remember that all VORs can only be received line-of-sight. Finally, high altitude VORs have the greatest range - 130 nm - between 18,000 feet agl and 45,000 feet agl, although they can also be effective at shorter ranges of 40 nm or more from 1,000 feet agl all the way through 60,000 feet agl. Low-altitude VORs are meant to be used from 1,000 feet agl through 18,000 feet agl at distances of up to 40 nm from the station. Terminal VORs are designed to be clearly received up to 25 nautical miles from the station at altitudes of 1,000 feet agl through 12,000 feet agl. Each VOR station can further be classified according to its range - terminal, low altitude, or high altitude. There are three types of VOR navigational stations: VOR (just the VOR), VOR-DME (VOR plus distance measuring equipment), and vortac (VOR plus the military's tactical air navigation system). Ironically, the very simple concept of opposites (To/From and Left/Right) creates an often confusing and abstract set of clues for pilots already hard at work flying the aircraft, communicating with air traffic control, and keeping track of the airspace they are using. Even as pilots depend on VOR navigation and the basic concepts involved, most pilots have difficulty mastering VOR techniques in their early training, and this confusion can linger well into their flying careers.
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