Definition
The rate at which an aircraft loses altitude over a given horizontal distance during a descent, typically expressed in feet per nautical mile or as a percentage. On instrument approaches, a published descent gradient defines the steepness of the descent path from one fix or altitude to the next.
Plain English
How steeply the aircraft is going down — how many feet of altitude are lost for each mile flown forward.
Context Anchor
Seen during instrument approaches, including monitored approaches, when comparing the airplane’s descent path with the expected path toward the runway.
Derivation
From Latin gradus, meaning 'a step' or 'a degree of slope.' A descent gradient is literally the 'step down' the aircraft takes per unit of distance flown.
Why Pilots Care
Following the correct descent gradient provides obstacle clearance and produces a stabilized approach to the runway threshold.
Analogy
It is like the grade of a road going downhill. The road is not described only by how fast a car moves down it, but by how much height it loses over the distance traveled.
Grounding Statement
Picture the airplane moving toward the runway while losing a set amount of altitude for each mile forward.
Intuition Check
Do not read descent gradient as just “how fast the airplane is going down.” It means how much altitude the airplane loses compared with how far it moves forward.
Example Sentence 1
The approach chart showed a descent gradient of 318 feet per nautical mile from the final approach fix to the runway.
Example Sentence 2
The published descent gradient of 318 feet per nautical mile kept the aircraft clear of terrain on the final segment.