VOR Flashcards
VOR Chart Reference
● VOR NAVAID data is indicated by the color BLACK on aviation charts, green is DME.
● The removal of the aural identification feature indicates the navaid is undergoing maintenance and should not be considered reliable
Advantages
● At these frequencies, precipitation static and other annoying interference that are caused by storms or various weather phenomena are not an issue.
● Accuracy:
➢ A tracking accuracy of plus or minus 1° is possible when flying a VOR radial
Disadvantages
● VOR signals transmitted by line-of-sight.
● Any obstacles (buildings, mountains or other terrain features, including the curvature of the earth) block VOR signals and restrict the distance over which they are received at a given altitude.
● Because of greater reception distances that we have at higher altitudes, it is also possible for an aircraft to receive erroneous indications due to the reception of two VOR stations operating on the same frequency.
● To prevent this stations with the same frequency are spaced as far apart as possible
How a VOR Works
● The VOR receiver receives an azimuth signal sent from the station.
● This azimuth FROM the station is called a RADIAL of the VOR.
● There are 360 useable radials oriented to magnetic north in the SDA.
Aircraft VOR Components
● Inside the aircraft there are two main components to the VOR
➢ The Receiver
➢ The Navigation Indicator
VOR Receiver
● In many modern aircraft one control unit is used as both the VOR receiver and the VHF communication transceiver.
● When located together the radio is called a NAVCOM.
Navigation Indicator
● The VOR navigation indicator gives the pilot the aircraft’s position relative to a radial
Omni Bearing Selector
● The radial selector, technically called the Omni Bearing Selector (OBS), is used to rotate the azimuth ring which displays the selected VOR radial at the top of the indicator.
● Flying a heading that is reciprocal to the bearing selected on the OBS would result in reverse sensing of a VOR receiver
● The TB needle has a 10° spread from centre to either side when receiving a VOR signal or 2.5° in LOC mode
Reference Line
● When the pilot selects a track, the position of another line is established, a reference line perpendicular to the track arrow and intersecting it at the station.
● The reference line divides the VOR reception area into two additional sectors
● The area forward of the reference line (on the same side as the aircraft) is the FROM envelope and the area to the rear of the reference line (on the side opposite the aircraft) is the TO envelope
● same side as radial is FROM, opposite side is TO
Area of Ambiguity
● Previously, aircraft between to/from boundaries are in the area of ambiguity.
● In this area, the opposing reference signals that actuate the TO FROM indicator cancel each other and produce an OFF indication.
● The area of ambiguity widens with increasing distance from the station.
● The greater the distance, the longer the TO or FROM flag will indicate OFF as the aircraft moves between the TO and FROM envelopes
Position Fix
● To determine a fix, without a DME, the pilot must use two VOR stations.
● A VOR gives only direction and not distance from the station.
● First, the pilot should tune the number one VOR to one of the desired stations
● After identifying the station, using the OBS knob, the pilot should centre the CDI needle with a FROM flag indication on the TO / FROM / OFF flag.
● The pilot repeats this procedure with the other VOR station
● Then, using the chart the pilot draws a line outbound from the VORs along the radials indicated by the track selector.
● The intersection of these bearings is the aircraft’s position
How to Test a VOR
● Before using a VOR it must be tested.
● There are several ways to do this
➢ VOT (VOR test)
➢ Self test
➢ Apron check sign
➢ Dual VOR check
➢ Geographical reference point
VOR Test
VOT
● VOR test frequency is in the CFS
➢ Spin OBS to 360 the CDI must centre +/- 4° with a FROM flag.
➢ Spin OBS to 180 the CDI must centre +/- 4° with a TO flag. Remember “Think 180 TO as in Cessna 182”
➢ Also check full scale deflection both ways by checking 10° from both sides of either 360° or 180° during the test
● same thing for self test found on Cessna radios
VOR Test
Checkpoint
● Airport sign for VOR checkpoint
➢ Taxi up beside a VOR test sign
➢ Follow directions
➢ Should indicate within +/- 4°
➢ DME should be within 0.5 NM of the posted distance
VOR Test
Dual VORs
● Dual VOR check using two receivers
➢ Tune in the two VOR receivers to the same station
➢ Select the same radial on the indicators
➢ Must indicate +/- 4°
Landmark
● Airborne geographical for a VOR test
➢ Fly over a landmark on a known and published radial
➢ Note the indicated radial on the VOR
➢ The reading should be within +/-6° of the published value
