FAA Aircraft Dispatcher (ADX)Flight Planning and PerformanceHard
An aircraft must clear obstacles requiring a climb gradient of 250 feet per nautical mile. If the aircraft's ground speed during the climb is 150 knots, what rate of climb (in feet per minute) is required to satisfy this gradient?
- A417 fpm
- B375 fpm
- C750 fpm
- D625 fpm
Show answer & explanationAnswer & explanation
Correct answer: D. 625 fpm
Rate of climb (fpm) = gradient (ft/NM) × ground speed (kt) ÷ 60. Calculation: 250 × 150 ÷ 60 = 37,500 ÷ 60 = 625 fpm.
Why the other options are wrong
- A. 417 fpm does not match the correct multiplication of gradient and ground speed.
- B. 375 fpm results from using an incorrect ground speed in the formula.
- C. 750 fpm overstates the required climb rate for this gradient and speed.
Climb Gradient to Rate of Climb
Converts a required obstacle clearance climb gradient (ft/NM) into a rate of climb (fpm) using ground speed.
- Formula: ROC (fpm) = Gradient (ft/NM) × GS (kt) ÷ 60
- Ground speed, not airspeed, is used
- Higher ground speed requires a higher rate of climb for the same gradient
Memory trick: 'Grade times speed, divide by sixty — that's the climb you need.'