Definition
An engine lubrication system in which the supply of oil is carried in a reservoir that is part of the engine itself, typically a sump located at the bottom of the crankcase. Oil drains back into this internal reservoir by gravity after circulating through the engine, and is then picked up and recirculated by the oil pump.
Plain English
A lubrication setup where the engine stores its own oil inside itself, in a built-in pan at the bottom. Oil is pumped up through the engine, does its job, then falls back down into that same pan to be used again.
Context Anchor
Seen in aircraft engine descriptions, oil servicing procedures, preflight oil checks, and maintenance discussions.
Derivation
‘Sump’ comes from the Middle Dutch ‘somp’, meaning a swamp or low pool — a place where liquid collects. ‘Wet’ here simply means the sump holds the oil supply. So a wet sump is literally the low spot in the engine that stays full of oil.
Why Pilots Care
Provides reliable oil circulation in normal flight but can lead to oil starvation during sustained inverted or aerobatic flight.
Intuition Check
Wet does not mean water is involved. Here, wet means the engine’s sump contains the oil supply.
Example Sentence 1
Most training aircraft use a wet-sump lubrication system, so the oil dipstick checks the supply directly inside the engine.
Example Sentence 2
Pilots of typical training aircraft check oil level in the wet-sump lubrication system using the engine dipstick during preflight.