Ground Speed

Ground speed (GS) is the horizontal speed of an aircraft relative to a fixed point on the earth's surface. It is the sum of the aircraft's true airspeed and the wind component along the flight path: a tailwind increases ground speed while a headwind decreases it.

Ground speed is critically important for:

• Navigation: Calculating ETAs and fuel burn for each waypoint
• Flight planning: Determining total trip time and required fuel
• ATC separation: Controllers use ground speed to maintain spacing between aircraft

Ground speed is displayed on the FMS and Navigation Display, typically derived from GPS, inertial navigation, or DME/DME updating. It can differ dramatically from indicated airspeed — a jet cruising at 250 KIAS at FL390 may have a true airspeed of 470 knots, and with a 150-knot jet stream tailwind, a ground speed exceeding 620 knots.