Definition
A descent flown with the engine(s) at or near idle power, allowing the aircraft to lose altitude using gravity rather than commanded thrust reduction beyond idle. Used in fuel-efficient descent profiles where the aircraft is configured to glide down at a planned speed and rate while engines produce minimum thrust.
Plain English
A descent where the pilot pulls the throttles back to the lowest normal power setting and lets the aircraft come down on its own, rather than using power to control the rate of descent.
Context Anchor
Seen in instrument procedure planning, descent management, and energy-management discussions, especially when planning how to meet altitude and speed restrictions efficiently.
Derivation
‘Idle’ comes from Old English idel, meaning ‘empty’ or ‘doing nothing useful.’ Here it refers to the engine running at its lowest steady setting — turning over but producing minimal thrust. Combined with ‘thrust descent,’ the term simply describes a descent flown with engines effectively contributing nothing to forward push.
Why Pilots Care
It provides a predictable, fuel-efficient way to lose altitude while maintaining precise control of airspeed and descent rate on published arrival routes.
Analogy
It is like taking your foot off the gas while driving downhill. The car still moves and may even speed up, so you manage the path and speed instead of adding power.
Grounding Statement
Picture the airplane aimed slightly downhill with the engines quiet at low power while the pilot manages speed and altitude toward the next restriction.
Intuition Check
Idle does not mean the engines are off. In an idle thrust descent, the engines are running at low power while the aircraft descends.
Example Sentence 1
The crew planned an idle thrust descent from cruise altitude to cross the arrival fix at 10,000 feet.
Example Sentence 2
During the arrival, an idle thrust descent kept the aircraft on the vertical profile without repeated power changes.