Definition
The mixing of air with a liquid, typically by drawing or forcing air into the fluid so that small bubbles become entrained throughout it. In aircraft systems, aeration is generally an unwanted condition in fluids such as engine oil and hydraulic fluid, because the resulting air bubbles compress under load and prevent the fluid from transmitting force or lubricating properly.
Plain English
Air getting mixed into a liquid, so the liquid becomes full of tiny bubbles. In airplane systems this is usually a problem, because air bubbles squish when squeezed and stop the fluid from doing its job.
Context Anchor
Seen in aircraft maintenance and system troubleshooting, especially with fuel, oil, brake, and hydraulic systems.
Derivation
From the Latin aer, meaning 'air,' with the suffix -ation indicating the act of doing something. So aeration is literally 'the act of putting air into something.'
Why Pilots Care
Aerated fuel can cause vapor lock, fuel pump cavitation, or engine hesitation, affecting safety and reliability.
Intuition Check
Aeration does not mean normal airflow or ventilation around the airplane. In this context, it means air mixed into a liquid.
Example Sentence 1
Aeration of the hydraulic fluid caused the brakes to feel spongy on the taxi out.
Example Sentence 2
Vigorous shaking of the fuel can during servicing introduced aeration that later caused rough running.