FAA Sport Pilot Airplane (SPA)Airspace and NavigationHard
A pilot measures the distance between two airports on a sectional chart using a plotter. According to the chart's graphic scale, 10 nautical miles corresponds to 1.35 inches. The measured distance between the airports is 8.1 inches. What is the approximate total distance between the airports?
- A54 nautical miles
- B10.8 nautical miles
- C60 nautical miles
- D81 nautical miles
Show answer & explanationAnswer & explanation
Correct answer: C. 60 nautical miles
The scale ratio is 1.35 inches = 10 NM, so 1 inch = 10/1.35 ≈ 7.41 NM. Multiplying: 8.1 inches × 7.41 NM/inch ≈ 60 NM. Alternatively, 8.1 ÷ 1.35 = 6, and 6 × 10 NM = 60 NM.
Why the other options are wrong
- A. 54 NM would result from multiplying 8.1 by an incorrect factor.
- B. This value results from an incorrect unit conversion, not the actual distance.
- D. 81 NM incorrectly treats the measured inches as directly equal to nautical miles.
Sectional Chart Distance Measurement
Distance on a sectional chart is measured using a plotter and the chart's graphic scale, then converted proportionally to nautical miles for flight planning.
- Sectional charts commonly use 1:500,000 scale
- Graphic scale bars show inches-to-nautical-miles ratio
- Proportional math: (measured inches ÷ scale inches) × scale NM
- Plotters often have a built-in nautical mile scale matching sectionals
Memory trick: Divide by the ratio, multiply by the truth