Definition
The minimum operating power setting of an aircraft engine, with the throttle fully retarded (closed), at which the engine continues to run smoothly without producing useful thrust for flight.
Plain English
The lowest power setting where the engine is still running but is producing almost no power. The throttle is pulled all the way back.
Context Anchor
In a steep spiral, the pilot may reduce power to idle to practice descending while managing airspeed and airplane control.
Derivation
From Old English "idel," meaning empty, useless, or not in active use. The aviation meaning carries the same idea: the engine is running but not actively doing the work of producing thrust.
Why Pilots Care
Using idle power in a steep spiral keeps descent rate and airspeed under control while leaving the engine ready for immediate power addition if needed.
Intuition Check
Idle does not mean the engine is stopped. It means the engine is running at its lowest normal power setting.
Example Sentence 1
To begin the steep spiral, the pilot reduced the throttle to idle and established a glide.
Example Sentence 2
With the engine at idle the airplane maintained a steady descent without excessive speed buildup.