Definition
A short tube cast or installed inside an air-cooled aircraft engine cylinder head that connects the intake port of one cylinder to the intake port of the cylinder on the opposite side of the engine, allowing a single intake pipe to feed two cylinders. In some engine designs, the term also refers to a tube that carries fuel/air mixture or oil between components on opposite sides of the engine.
Plain English
A pipe that runs across the engine to share intake mixture between two cylinders on opposite sides, so one feed line can supply both.
Context Anchor
Seen during engine-compartment inspections, exhaust-system maintenance, and discussions of cabin heat or carburetor heat on piston aircraft.
Derivation
From 'cross over,' meaning to pass from one side to the other. The tube literally crosses the engine to reach a cylinder on the opposite side.
Why Pilots Care
A cracked or leaking crossover tube allows unmetered air into the intake, leaning the mixture for the affected cylinders. This can cause rough running, loss of power, and in extreme cases detonation or cylinder damage.
Intuition Check
Do not read crossover tube as any tube that happens to pass across the engine. In this context, it is a designed exhaust-system pipe that carries exhaust gas from one side or section to another.
Example Sentence 1
The mechanic traced the rough idle to a leaking crossover tube between cylinders three and four.
Example Sentence 2
A clogged crossover tube caused uneven mixture distribution and rough running on the right cylinder bank.