Definition
Discharged or vented from the aircraft to the outside air, typically through a dedicated port or drain on the airframe.
Plain English
Sent out of the aircraft into the surrounding air, usually through a small opening built into the structure for that purpose.
Context Anchor
Seen in aircraft system discussions, especially where air, fluid, fumes, or pressure must be carried safely outside the airplane.
Derivation
From the nautical term 'overboard,' meaning 'over the side of a ship and into the water.' In aviation it kept the same flavour — something leaving the vehicle for the outside environment — but the 'outside' is now the air rather than the sea.
Why Pilots Care
Many engine and system components rely on venting overboard to work correctly. A blocked overboard line can cause oil to back up, pressure to build, or a system to fail, so pilots may see oil streaks on the belly or smell fumes if something is venting that shouldn't be.
Intuition Check
Overboard does not mean something has fallen off by accident. Here it usually means the aircraft is intentionally sending air, fluid, fumes, or pressure outside through a designed path.
Example Sentence 1
Excess oil from the crankcase breather is vented overboard through a tube on the underside of the cowling.
Example Sentence 2
During preflight, the pilot confirmed the carburetor overflow line routes fuel overboard.