Flight Time
Time en route equals distance divided by ground speed.
Formula
Variables
Example
300 nm at 150 kt GS: t = 2 h
How it works
This formula gives the time an aircraft spends travelling a known distance when its ground speed is known. It works because speed is distance per unit time, so rearranging the speed relationship gives time = distance ÷ speed. In aviation, ground speed is used instead of airspeed because flight time depends on how fast the aircraft is moving over the ground.
When to use it
Use this when you know the distance between two points and the aircraft’s ground speed, and you need an estimate of en route time. It is common in flight planning, navigation problems, and quick checks of how long a leg will take.
Worked example, step by step
A flight covers 450 nm with a ground speed of 180 kt. Use the formula: t = d / GS Substitute the values: t = 450 / 180 Calculate: t = 2.5 So the flight time is 2.5 hours, which is 2 hours 30 minutes.
Common mistakes to avoid
- Using airspeed instead of ground speed
- Forgetting to keep units consistent, especially nm and kt
- Dividing speed by distance instead of distance by speed
Did You Know?
Flight planners compute time from ground speed, not airspeed — the wind makes all the difference.
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