Plain English Meaning

Cabin heat in most small piston aircraft is made by passing fresh outside air around the hot exhaust pipe and then sending that warmed air into the cockpit. It is simple and effective, but a leak in the exhaust pipe can let poisonous fumes into the cabin along with the heat.

Full Definition

A cabin heating system on light aircraft that warms outside air by routing it through a shroud or jacket surrounding the engine's hot exhaust pipe (muffler). The heated air is then ducted into the cabin and to the windshield defroster. Because the heating air passes near hot exhaust gases, any crack or leak in the exhaust system can allow carbon monoxide to enter the cabin.