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Calculate the ground distance in km, on an ATS route between VORs, if the distance on the en-route chart measures 200 mm and the quoted scale is 1 inch = 20 NM.
  • A
    181 km
  • B
    292 km
  • C
    157 km
  • D
    370 km

Charts represent the “reduced earth”.
The chart scale represents the relation between the length represented on the chart compared with the real distance on planet earth.

Chart Scale = Chart length / Earth distance

As the units of length are in different units, first we must convert them for the same units:

1 nm = 1.852 km
20 nm = 37,04 km = 3 704 000 cm
1 in = 2.54 cm

Chart Scale = 2.54 / 3 704 000 = 1/1 458 268

With the chart scale defined, calculate how many km are presented by 200 mm distance on the chart:

20 cm x 1 458 268 cm = 29 165 360 cm = 292 km

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