20 January 2015

VHF Omnidirectional Range (VOR)

How does it work?
  • it depends upon a phase difference between two signals transmitted simultaneously from a ground station
  • position sensitive, NOT azimuth (i.e. no matter what direction you are facing, your instruments will give you the same VOR information about your position)
  • line of sight: reception distance = 1.23 x sqrt(altitude above station)

Components:
  • Omni Bearing Selector (OBS) >> select radials "FROM top, TO bottom"
  • Course Deviation Indicator (CDI needle) >> centre to full scale is 10 degrees
  • TO / FROM indicator >> directional ambiguity when crossing a radial 90 degrees from what is set on OBS

Tolerances:
  • airway radials maintained by TC within +/- 3 degrees
  • VOR checkpoint +/- 4 degrees
  • dual VOR check +/- 4 degrees on ground or in air
  • visual check over landmark +/- 6 degrees

To calculate distance (NM) from station:
  • (groundspeed x time in minutes) / degrees of bearing change

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