Definition
A descent profile flown with the engines at or near flight idle thrust, allowing the aircraft to lose altitude using gravity and aerodynamic drag rather than commanded thrust. In VNAV operations, the flight management system computes this path so that a continuous descent from cruise to a defined endpoint can be made without adding power, optimizing fuel burn and noise.
Plain English
A planned descent where the engines are pulled back to their lowest normal setting and the aircraft glides down along a calculated slope. The computer works out the right point to start coming down so that idle thrust alone gets the aircraft to the target altitude.
Context Anchor
Seen in VNAV planning, FMS descent calculations, and vertical profile displays that help the pilot plan the descent from cruise.
Derivation
‘Idle’ here means the engine setting where it produces minimum thrust while still running normally — not ‘doing nothing.’ ‘Descent path’ is the calculated track the aircraft follows downward. Together, the phrase describes a downward path designed around minimum engine power.
Why Pilots Care
Ensures the aircraft meets altitude restrictions efficiently while controlling speed and conserving fuel.
Grounding Statement
Picture the airplane starting down with the power set low, trading altitude for forward motion along a planned downhill line.
Intuition Check
“Idle” does not mean the engines are off or that the airplane is uncontrolled. Here, it means the engines are running at a low power setting while the aircraft follows a planned descent path.
Example Sentence 1
The FMS calculated the top-of-descent point so the aircraft could follow an idle descent path all the way down to the arrival fix.
Example Sentence 2
During the arrival the aircraft stayed on the idle descent path without needing extra power.