Definition
The section of a reciprocating aircraft engine, typically mounted at the rear of the crankcase, that provides mounting points and internal drives for engine accessories such as magnetos, fuel pumps, oil pumps, vacuum pumps, tachometer drives, and starter and generator/alternator units.
Plain English
It is the part of the engine where the smaller engine-driven components are bolted on and powered by gears connected to the crankshaft.
Context Anchor
Seen in reciprocating engine diagrams and maintenance descriptions when locating where engine-driven accessories are mounted.
Derivation
Accessory comes from the Latin accessorius, meaning 'something added or supplementary.' Housing simply means an enclosure. Together it describes the enclosed section that holds the engine's supplementary equipment — the parts that support the engine but are not part of the core power-producing assembly.
Why Pilots Care
Failure of the accessory housing or its gears can disable ignition, electrical power, or fuel delivery, directly affecting engine operation and safety.
Intuition Check
Do not read accessory as meaning optional or unimportant here. In an aircraft engine, many accessories mounted on the accessory housing are essential to normal engine operation.
Example Sentence 1
The magnetos and fuel pump are mounted on the accessory housing at the back of the engine.
Example Sentence 2
After an engine change, the mechanic verified that all bolts securing the accessory housing were properly torqued.