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A pilot flying an aircraft at FL 80 tunes in a VOR which has an elevation of 313 m. Given ISA conditions, what is the maximum theoretical distance at which a pilot can receive the VOR signals?
  • A
    100 NM
  • B
    180 NM
  • C
    149 NM
  • D
    120 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).

Before filling in the formulae, a conversion has to be made using the the following table:

1 m 3.28 ft
313 m ?

? = (313 m x 3.28 ft)/(1 m ) = 1026 ft

Knowing that:

H1 = 8000 ft
H2 = 1026 ft
Filling in the formulae gives the following:
Max range = 1.23 x √8000 + 1.23 x √1026 = 110 + 39 = 149 nm

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