Which term describes the speed of the aircraft relative to the ground as used in navigation?

• A. Airspeed
• B. Groundspeed
• C. Indicated Airspeed
• D. True Airspeed

Answer: (B)

Groundspeed is the speed of the aircraft relative to the surface, and it’s the value pilots use for navigation calculations, such as time en route and distance covered. It results from the aircraft’s motion through the air combined with the wind flowing over the earth—the wind effectively pushes or resists your movement over the ground. For example, if you’re moving through the air at 120 knots and a tailwind of 20 knots is blowing, your speed over the ground increases to about 140 knots; a headwind would reduce it. This differs from indicated airspeed, which is what the airspeed indicator shows and is primarily about the aircraft’s performance and stall margins, and true airspeed, which is the aircraft’s speed through the air corrected for altitude and temperature. Groundspeed is what you use to estimate arrival time and fuel needs because it reflects actual progress over the Earth.