FAA Flight Instructor Airplane (FIA)Performance, Weight and BalanceMedium
An airplane climbs at a steady rate of 600 fpm while maintaining a groundspeed of 100 knots. What is the approximate climb gradient in feet per nautical mile?
- A180 ft/nm
- B360 ft/nm
- C720 ft/nm
- D600 ft/nm
Show answer & explanationAnswer & explanation
Correct answer: B. 360 ft/nm
Climb gradient (ft/nm) = ROC (fpm) × 60 ÷ groundspeed (kt) = 600 × 60 ÷ 100 = 360 ft/nm.
Why the other options are wrong
- A. Half the correct value; likely from dividing incorrectly.
- C. Overstates the gradient by using wrong groundspeed factor.
- D. Confuses rate of climb (fpm) directly with gradient (ft/nm).
Climb Gradient vs Rate of Climb
Rate of climb (fpm) measures vertical speed over time; climb gradient (ft/nm) measures altitude gained per horizontal distance and depends on groundspeed.
- Gradient (ft/nm) = ROC × 60 ÷ GS
- Same ROC gives different gradients at different groundspeeds
- Obstacle clearance charts use gradient, not ROC alone
- Slower groundspeed steepens the climb gradient for a given ROC
Memory trick: 'Rate is time, gradient is ground' — two different climb yardsticks.