In aviation, the rule of three or "3:1 rule of descent" is a rule of thumb that 3 nautical miles (5.6 km) of travel should be allowed for every 1,000 feet (300 m) of descent.[1][2] For example, a descent from flight level 350 would require approximately 35x3=105 nautical miles. This would have to be adjusted for headwind or tailwind,[1] and also to allow for deceleration time.

Alternatively, David P. Davies gives the rule as 300 feet of descent required for each nautical mile of distance.[3]: 176 

Large aircraft approaching to land normally use a 3 degree approach path.[4] This is equivalent to 3.14 nautical miles per 1000 ft of descent. If exactly 3 nmi are allowed per 1000 ft of descent, the glide path will be 3.14 degrees.

See also

References

  1. 1 2 Instrument Procedures Handbook (IPH) AA-H-8083-16B. Federal Aviation Administration. 2017. pp. 3–6.
  2. ↑ "Top 10 rules of thumb". Plane and Pilot Magazine. 2006-01-01. Retrieved 5 November 2012.
  3. ↑ Davies, David P. (1971). Handling the Big Jets: An Explanation of the Significant Differences in Flying Qualities Between Jet Transport Aeroplanes and Piston Engined Transport Aeroplanes, Together with Some Other Aspects of Jet Transport Handling. Air Registration Board. ISBN 0903083019.
  4. ↑ Dillman, Donald R. (February 1990). Swing Low Sweet Chariot. The MAC Flyer. p. 10. Retrieved 20 June 2022.
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