Groundspeed

Groundspeed is the aircraft's speed over the ground. It is a vector result that depends on true airspeed, heading, wind speed, and wind direction. A headwind lowers groundspeed, while a tailwind raises it for the same true airspeed.

How it works

An aircraft moves through an air mass at its true airspeed. The air mass itself moves over the ground with the wind. Adding those two vectors produces the aircraft's groundspeed and track. A crosswind can change both the direction of travel and the groundspeed, even when the aircraft maintains a constant airspeed.

Groundspeed is different from true airspeed, which describes movement through the surrounding air. It is also different from indicated airspeed, which is the cockpit pressure reference used for many operating speeds.

Example

An aircraft has a true airspeed of 110 knots and a direct 20-knot headwind. Its approximate groundspeed is 90 knots. With a direct tailwind of the same speed, the approximate groundspeed is 130 knots. A crosswind requires vector addition rather than simple subtraction.

Why it matters

Groundspeed is used to estimate time over a route, arrival time, and distance traveled. It changes as wind changes, so a single cruise calculation may not represent the entire flight. Navigation equipment can display groundspeed from position updates, but the displayed value still depends on the quality and timing of the data.

Use current wind forecasts and the aircraft's approved navigation equipment for planning. A groundspeed estimate is not a substitute for fuel reserves or required flight planning.

Related terms and tools

• True airspeed
• Track
• FAA Pilot's Handbook of Aeronautical Knowledge