Definition
A device that removes air and other entrained gases from a liquid, typically engine oil, before the liquid is returned to the system or reservoir. In a dry-sump aircraft engine, the deaerator separates air bubbles from scavenged oil so that only de-aerated oil is delivered back to the oil tank.
Plain English
A part that takes the air bubbles out of the oil before the oil is sent back to the tank, so the engine receives clean liquid oil instead of foamy oil.
Context Anchor
Seen in aircraft powerplant oil system descriptions, especially where oil returns from the engine with air mixed into it.
Derivation
From 'de-' meaning 'remove' and 'aerator' meaning 'something that adds air.' A deaerator does the opposite of an aerator: it takes air out. Knowing this makes the function obvious from the name.
Why Pilots Care
Air in the oil can reduce lubrication effectiveness, cause pump cavitation, and lead to engine wear or failure.
Intuition Check
A deaerator is not mainly a filter for dirt. Its job is to remove air mixed into the oil.
Example Sentence 1
The scavenge oil passes through the deaerator before returning to the oil tank, where it can settle and be drawn back into the engine.
Example Sentence 2
Proper operation of the deaerator keeps the oil pressure steady during high-power climbs.