Definition
Groundspeed is the actual speed of the aircraft over the ground. It is true airspeed adjusted for wind — increased by a tailwind and decreased by a headwind.
Plain English
How fast the airplane is actually moving across the ground below it. A 120-knot airplane flying into a 20-knot headwind is only covering ground at 100 knots.
Context Anchor
Seen in airspeed, navigation, and flight planning discussions, especially when estimating time to a destination.
Why Pilots Care
Groundspeed directly determines estimated time of arrival and fuel burn, so it affects route decisions and safety margins.
Analogy
Think of swimming across a river. Your swimming speed is your airspeed — how fast you move through the water. But the current carries you downstream. Your groundspeed is how fast someone watching from the bank sees you actually move.
Intuition Check
Do not assume groundspeed is the same as the speed shown on the airspeed indicator. Groundspeed is movement over the ground; indicated airspeed is based on air pressure sensed by the airplane.
Example Sentence 1
With a 25-knot tailwind, our true airspeed of 110 knots gave us a groundspeed of 135 knots, so we arrived ten minutes early.
Example Sentence 2
The pilot noted a drop in groundspeed and adjusted power to maintain the planned arrival time.