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SESK: Stuff Everyone Should Know · sesk.info/pilot-groundspeed-flight-time

A 400-nautical-mile flight at 100 knots groundspeed takes how long?

It takes 4 hours.

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  1. 2 hours
  2. 3 hours
  3. 4 hours ✔

Why: Time equals distance divided by groundspeed. Dividing 400 nautical miles by 100 nautical miles per hour gives 4 hours.

Huh, didn't know that: Groundspeed, not indicated airspeed, determines en route time.

The dad joke
Why was the flight computer calm? It knew time would divide the distance.
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References

Answer: 4 hours. Time equals distance divided by groundspeed. Dividing 400 nautical miles by 100 nautical miles per hour gives 4 hours.

  1. FAA Pilot's Handbook of Aeronautical Knowledge, Chapter 16 www.faa.gov/sites/faa.gov/files/18_phak_ch16.pdf
    a flight of 400 NM at 100 knots GS takes 4 hours to complete
    Checked 2026-10-09.

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