Definition
The part of a reciprocating or turbine aircraft engine where engine-driven accessories are mounted and powered. These accessories typically include magnetos, fuel pumps, oil pumps, generators or alternators, vacuum pumps, tachometer drives, and starters. The accessory section contains the gear train that takes power from the engine's crankshaft (or turbine shaft) and drives each accessory at its required speed.
Plain English
The area on the back of the engine where things like the fuel pump, oil pump, magnetos, and alternator are bolted on and driven by the engine itself.
Context Anchor
Seen in aircraft engine descriptions, maintenance manuals, and preflight or troubleshooting discussions involving the rear of the engine.
Derivation
Accessory comes from the Latin accedere, meaning to approach or be added to. An accessory is something added on to support the main item. The accessory section is the part of the engine where these added-on components live.
Why Pilots Care
A failure in the accessory section can stop the generator, magnetos, or fuel pump even though the engine itself is still turning, leading to loss of electrical power or ignition.
Intuition Check
Do not assume “accessory” means optional here. In this engine context, an accessory may be an attached part that is essential for safe operation.
Example Sentence 1
The mechanic removed the magneto from the accessory section to check its timing.
Example Sentence 2
Oil pressure dropped after a gear in the accessory section sheared, disabling the vacuum pump.