Definition
The mathematical expression used to convert a required climb gradient (expressed in feet per nautical mile) into a required rate of climb (expressed in feet per minute) for a given groundspeed. The standard form is: Rate of Climb (ft/min) = (Climb Gradient in ft/NM × Groundspeed in knots) ÷ 60.
Plain English
A simple calculation that turns a published climb requirement (so many feet of altitude gained for every mile flown) into a number you can actually fly on the cockpit vertical speed indicator (so many feet gained per minute), based on how fast you're moving over the ground.
Context Anchor
Seen in instrument departure planning, especially when checking whether an aircraft can meet a required climb gradient for obstacle clearance.
Derivation
The word 'gradient' comes from the Latin gradi, 'to step or walk,' and was adopted in surveying and engineering to describe the steepness of a slope. A climb gradient describes the steepness of the airplane's climb path through the air over the ground.
Why Pilots Care
Aircraft performance must meet or exceed the published value to guarantee obstacle clearance in instrument conditions.
Grounding Statement
If the airplane covers ground quickly but climbs slowly, the climb gradient becomes smaller because the airplane gains fewer feet for each mile traveled.
Intuition Check
Do not confuse climb gradient with rate of climb. Rate of climb is feet per minute; climb gradient is feet gained per nautical mile across the ground.
Example Sentence 1
The departure procedure required a 350 ft/NM climb gradient, so at a groundspeed of 120 knots the pilot used the climb gradient formula to calculate a required rate of climb of 700 feet per minute.
Example Sentence 2
During the missed approach the aircraft must maintain the climb gradient formula requirement of 3.3 percent to remain clear of obstacles.