Definition
Engine oil that has escaped from the engine and is visible on the aircraft, typically streaking back from the engine cowling, breather tube outlet, or oil filler area. It indicates either normal venting of a small amount of oil through the breather, or an abnormal leak from a seal, gasket, fitting, or component.
Plain English
Oil that has come out of the engine and shows up on the outside of the airplane. A small amount is normal, but a lot means something is leaking and needs to be checked.
Context Anchor
Seen during securing, servicing, preflight inspection, or postflight checks when looking for oil on the engine area, underside of the airplane, or the ground.
Derivation
Oil comes from an old word meaning olive oil or oily liquid. Discharge means to unload or release something. Together, the words point to oil being released from where it was being held.
Why Pilots Care
Small amounts are often normal, but excessive discharge can indicate overfilled oil, worn rings, or other engine conditions that affect airworthiness.
Intuition Check
Do not read discharge here as an electrical discharge or as paperwork. In this context, it means oil physically coming out of the aircraft engine or oil system.
Example Sentence 1
During preflight, the pilot noticed fresh oil discharge along the belly of the aircraft and asked a mechanic to inspect the engine before flight.
Example Sentence 2
The instructor pointed out that a few drops of oil discharge after a flight is normal but a steady stream requires checking the oil level before the next flight.