Climb Gradient to Rate of Climb
Reconciles a departure's climb GRADIENT (feet per nautical mile, the obstacle-clearance slope) with the cockpit rate of climb (feet per minute) through the ground speed: ROC = gradient x ground speed / 60. A 300 ft/nm gradient at 120 kt needs 600 ft/min; the gradient as a percent is ft/nm over 6076.12 (the 200 ft/nm default is ~3.3%). The trap: because it scales with GROUND speed, flying faster or a tailwind demands a HIGHER rate of climb for the same gradient, and a heavy, high-density-altitude departure may not make a steep gradient at all -- the takeoff go/no-go. A planning aid; the departure procedure and performance charts govern.
Formula and source
roc_fpm = climb_gradient_ft_per_nm x ground_speed_kt / 60; gradient_percent = climb_gradient_ft_per_nm / 6076.12 x 100; gradient_deg = atan(climb_gradient_ft_per_nm / 6076.12).
Climb gradient to rate of climb (FAA TERPS / AIM departure procedures), by name; the departure procedure and aircraft performance charts govern.
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