Measurement of Distance

Wg Cdr Rajagopal

Measurement of Distance on Earth Surface

Index

Distance Measurement for Air Navigation

  • Distance measurement is important for pilots to keep track of aircraft position
  • Horizontal distances are measured in Nautical Miles, Kilometres or Statute Miles
  • Vertical distances are measured in feet or meters

Nautical Mile

  • One nautical mile is the length of a meridian subtending an angle of 1 minute of arc at its centre of curvature
  • At equator, curvature of earth is maximum
  • Since highly curved lines require lesser distance per unit angle, the length of nautical mile is minimum at equator
  • At the equator, one nautical mile is equal to 6048 feet
  • At the poles, curvature of earth is minimum
  • Since, less curved lines require greater distance per unit angle, the length of nautical mile is maximum at poles
  • At poles, one nautical mile is equal to 6108 feet

Value of Nautical Mile used in Air Navigation

  • International Civil Aviation Organisation defines a nautical mile as 1852 meters
  • International nautical mile is 6076.1 ft or 1852 meters is the average value of a nautical mile
  • Standard or Admiralty nautical mile is 6080 ft that is practically used for navigation calculations
  • Equator to either pole subtends 90 degrees or 5400 minutes of latitude
  • Considering 1 min as 1 NM, circumference of earth is equal to 21,600 NM

Kilometre

  • Kilometre is defined as 1/10,000 part of the average distance from Equator to either Pole
  • Distance from equator to either pole is taken to be 10,000 km and one kilometre is one by ten thousand part of this distance
  • By definition of kilometre, the circumference of earth is 40,000 km

Statute Mile

  • Statute mile is a measurement of distance defined by law or statute
  • One statute mile is equal to 5280 feet

Conversion Factors

  • We have seen that 21,600 Nm is equal to 40,000 Km which form the basis for other conversion factors
  • 1 Nautical Mile = 1.85 kilometres = 1.15 Statute Miles
  • 1 Nautical Mile = 6080 Feet = 1852 Meters
  • 5.4 Nautical Mile = 10 kilometres
  • 1 kilometre = 3280 feet

Best of luck