A headwind of 15 knots reduces your ground speed. If your true airspeed is 105 knots, what is the approximate ground speed?

• A. 80 knots
• B. 85 knots
• C. 95 knots
• D. 90 knots

Answer: (D)

Ground speed is how fast you move over the ground, and it’s what you get when you adjust your true airspeed for the wind along your path. When a headwind blows directly against you, it reduces your progress over the ground, so you subtract the wind speed from your true airspeed.

Here, your true airspeed is 105 knots and the headwind is 15 knots. Subtracting gives 105 − 15 = 90 knots. So the approximate ground speed is 90 knots.

If the wind weren’t directly opposing, you’d need a vector approach to find the effective wind component along your track, but for a straightforward headwind of 15 knots, simple subtraction yields the correct result.