Plain English Meaning

If you know how fast you are moving across the ground and how long you have been moving, you can work out how far you have gone by multiplying the two together.

Full Definition

A navigation formula stating that distance traveled (D) equals groundspeed (GS) multiplied by time (T). Used to calculate how far an aircraft will travel, or has traveled, when groundspeed and elapsed time are known. Groundspeed must be expressed in the same time unit as T (for example, knots with hours yields nautical miles).

Context Anchor

Used in cross-country planning, navigation log calculations, and in-flight estimates of how far the airplane will travel before the next checkpoint.

Derivation

D, GS, and T are simply the first letters of Distance, Groundspeed, and Time. The formula is the relationship between , time, and distance, applied here using groundspeed (speed the ground) rather than , because navigation is concerned with progress across the earth's , not movement through the .