FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsHard
A landing distance chart shows a no-wind ground roll of 450 feet. Using the general rule that ground roll decreases approximately 10% for each 9 knots of headwind component, what is the approximate landing ground roll with an 18-knot headwind?
- A315 feet
- B360 feet
- C450 feet
- D405 feet
Show answer & explanationAnswer & explanation
Correct answer: B. 360 feet
18 knots of headwind is two increments of 9 knots, giving a 20% reduction. 450 feet × 0.80 = 360 feet ground roll.
Why the other options are wrong
- A. This overestimates the reduction beyond the correct 20%.
- C. This ignores the headwind correction entirely.
- D. This applies only a 10% reduction, accounting for only one 9-knot increment.
Headwind Effect on Landing Distance
A general rule of thumb states that ground roll (takeoff or landing) decreases by approximately 10% for every 9 knots of headwind component.
- Headwind reduces both takeoff and landing ground roll
- Rule of thumb: 10% reduction per 9 knots of headwind
- Tailwind has the opposite, and much larger, adverse effect
Memory trick: Nine knots knocks off ten percent, every time.