Definition
The angle between the aircraft's actual flightpath through the air and the horizontal. In a climb, this angle is positive (path tilted upward); in a descent, it is negative (path tilted downward); in level flight, it is zero.
Plain English
How steeply the airplane is actually traveling up or down through the air, measured as an angle from level.
Context Anchor
Seen in instrument flying discussions of climbs, where pitch, power, airspeed, and rate of climb are being compared.
Derivation
From Latin 'inclinare,' meaning 'to lean' or 'tilt.' Flightpath is simply the path the aircraft is flying through the air. Together: how much that path is tilted from level.
Why Pilots Care
Directly determines climb rate for a given airspeed and affects how quickly altitude is gained or lost.
Grounding Statement
Picture the aircraft leaving a slanted line behind it in the sky; the inclination is the steepness of that line.
Intuition Check
Do not read this as just “where the nose is pointing.” Here, it means the steepness of the airplane’s actual path through the air.
Example Sentence 1
During the climb, the inclination of the flightpath was about five degrees above the horizontal.
Example Sentence 2
Reducing power lowers the inclination of the flightpath and the airplane begins a gradual descent.