Definition
The rate of altitude gain achieved by a multi-engine aircraft during the takeoff and climb phase with all engines producing normal takeoff power, expressed as a ratio of height gained to horizontal distance traveled (commonly stated as a percentage or in feet per nautical mile).
Plain English
How steeply the aircraft can climb after takeoff when every engine is working normally. It is measured as how many feet the aircraft goes up for each unit of distance it travels forward.
Context Anchor
Seen in takeoff and departure planning, especially when comparing normal climb performance with obstacle clearance needs after takeoff.
Derivation
A 'gradient' comes from the Latin 'gradus' meaning 'step' or 'degree of slope.' In aviation, a climb gradient describes the slope of the aircraft's flight path through the air, the same way a road gradient describes the slope of a hill.
Why Pilots Care
Establishes the baseline performance used to confirm that an aircraft can still meet required obstacle clearance even if one engine fails.
Analogy
It is like a road grade, but in the air: the higher the gradient, the more height is gained over the same forward distance.
Intuition Check
Do not read “all-engines-operating” as meaning “guaranteed obstacle clearance.” It only describes the aircraft’s climb condition: every engine is working. Do not read “climb gradient” as vertical speed alone. It is climb compared with forward distance.
Example Sentence 1
The departure procedure required an all-engines-operating climb gradient of 250 feet per nautical mile until reaching 3,000 feet.
Example Sentence 2
During preflight planning the crew verified that the all-engines-operating climb gradient supported a safe initial climb to the first fix.