Definition
The period during which a piece of equipment, fluid, or component is allowed to sit at a particular temperature long enough for the entire mass to reach that temperature throughout. Commonly referenced as a 'cold soak' (extended exposure to very low temperatures, such as fuel at altitude or an aircraft parked overnight in cold conditions) or a 'heat soak' (residual heat retained in an engine or component after shutdown).
Plain English
Letting something stay in a hot or cold environment long enough for the heat or cold to work its way all the way through it, not just on the surface.
Context Anchor
Seen in maintenance instructions for heating, treating, or repairing aircraft metal parts.
Derivation
From the everyday sense of soaking something in liquid until it is saturated through and through. The aviation usage keeps that idea but applies it to temperature: the object is 'soaked' in heat or cold until fully saturated at that temperature.
Why Pilots Care
Cold-soaked fuel can chill the upper wing surface enough to form clear ice even in dry air, and a heat-soaked turbine engine needs a proper cool-down before shutdown to prevent uneven cooling and bowed shafts. Knowing whether a component is soaked at temperature affects both preflight inspection and engine handling.
Intuition Check
Do not assume soak always means putting something in liquid. In this maintenance use, it usually means holding a part at a set temperature for a set time.
Example Sentence 1
After a long cruise at altitude, the wing tanks were cold-soaked, so the crew watched closely for clear ice forming on the upper wing surface during the turnaround.
Example Sentence 2
Maintenance requires a thirty-minute soak after shutdown to equalize temperatures in the turbine section.