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In ISA conditions, approximately what is the maximum theoretical range at which an aircraft at FL210 may expect to receive signals from a VOR facility sited 340 feet above mean sea level?
  • A
    245 NM
  • B
    183 NM
  • C
    163 NM
  • D
    201 NM

The VHF Omni-Range (VOR) station uses Very High Frequency (VHF) radiowaves to transfer information.
The formulae used to calculate the range of these radio waves is as follows:
Maximum theoretical range (in nm) = 1.23 x √H1 + 1.23 x √H2

H1 = the height in feet of the transmitter above mean sea level (MSL).
H2 = the height in feet of the receiver above mean sea level (MSL).

Knowing that:

H1 = 21.000 ft
H2 = 340 ft

Filling in the formulae gives the following:

Max range = 1.23 x √21.000 + 1.23 x √340 = 178 + 23 = 201 nm

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