Definition
A reservoir, usually formed by the lower portion of the engine crankcase, that holds the supply of lubricating oil for a reciprocating aircraft engine. Oil drains back into the sump after circulating through the engine and is drawn from there by the oil pump for re-circulation.
Plain English
The tank at the bottom of the engine where the engine's oil collects and is stored between trips through the engine.
Context Anchor
You will encounter this term in engine lubrication discussions, preflight oil checks, maintenance descriptions, and engine system diagrams.
Derivation
Sump comes from the Middle English word for a marsh or pit where liquid collects. In an engine it carries the same idea — a low spot where oil settles after doing its job, ready to be picked up and used again.
Why Pilots Care
Maintaining the correct oil quantity in the sump prevents engine damage from inadequate lubrication.
Analogy
Think of it like the low spot in a pan where liquid gathers. The oil collects there before being sent back through the engine.
Intuition Check
Do not think of the sump as a separate fuel-style tank. In this context, it is the low oil-collection area of the engine, not where fuel is stored.
Example Sentence 1
Before flight, the pilot checked the dipstick and confirmed the engine oil sump held seven quarts.
Example Sentence 2
During the oil change the mechanic drained the engine oil sump completely before refilling with fresh oil.