How is reference groundspeed computed?

Reference groundspeed is computed by subtracting the surface headwind component from the approach true airspeed. This method accurately reflects the aircraft's speed over the ground because it recognizes the effect of wind on the aircraft's movement.

When an aircraft is in flight, its true airspeed is the speed at which it moves through the air, but to determine how fast it is actually moving over the ground, wind effects must be accounted for. A headwind, which opposes the direction of flight, would decrease the groundspeed, so when calculating reference groundspeed, this headwind component is subtracted from the true airspeed. This gives a clear picture of the aircraft's performance relative to the ground, which is critical for approaches and landings.

The other options do not accurately represent how reference groundspeed is computed. For instance, adding tailwind components would incorrectly increase the groundspeed rather than provide the accurate measure needed for landing calculations. Similarly, calculating average speed during climb or using takeoff airspeed does not account for real-time wind effects during an approach. These approaches may provide useful data in other contexts but do not serve the purpose of determining reference groundspeed accurately.