What it is: GS shows how fast your aircraft is covering distance across the terrain or along its route, rather than how fast it is moving through the air mass. That means it changes with headwinds, tailwinds and, to a lesser extent in practical use, your track across the ground.
In practice: During a simulated flight, GS matters for time and navigation more than aircraft handling. A strong headwind lowers GS and increases en-route time and fuel burn for a given distance, while a tailwind does the opposite. Flight plans, FMC predictions, GPS displays and moving maps all use GS to estimate arrival times and distance remaining. On approach, a high GS can also mean you cover miles quickly even when indicated airspeed looks normal, which affects descent planning and spacing.
Key considerations:
- Do not confuse GS with indicated airspeed: the aircraft flies by airspeed, but navigation timing and ETA depend on GS.
- Large wind differences between forecast and actual conditions can make FMC arrival predictions and top-of-descent points shift during flight.
