Definition
A descent maintained for an extended period at low or idle power, during which the engine receives little fuel and operates at reduced temperatures, increasing the risk of engine cooling, spark plug fouling, and carburetor or induction icing if not managed with periodic power applications and proper mixture handling.
Plain English
A long, drawn-out descent where the engine is running at very low power for a while, which can let the engine cool too much, foul the spark plugs, or allow ice to form unless the pilot adds power now and then.
Context Anchor
Seen when descending from cruise altitude toward an airport, a practice area, or a lower assigned altitude.
Derivation
Prolonged comes from roots meaning “lengthened” or “made longer.” Descent comes from a Latin word meaning “to climb down.” Together, they point to a descent that continues for an extended time, not a short drop in altitude.
Why Pilots Care
Unmanaged prolonged descents can cause shock cooling of the cylinders, carburetor icing, or loss of propeller control, all of which affect safety and maintenance costs.
Intuition Check
Do not read prolonged descent as simply “any descent that feels long.” In this FAA context, the key idea is an extended descent that requires continued control of speed, power, and engine condition.
Example Sentence 1
During the prolonged descent from 9,500 feet, the pilot briefly added power every thousand feet to keep the engine warm.
Example Sentence 2
Before entering a prolonged descent through moist air, the pilot selected carburetor heat to prevent icing.