Definition
The end of a reciprocating or turbine aircraft engine where the accessory drives are located. These drives power components such as magnetos, fuel pumps, oil pumps, generators or alternators, hydraulic pumps, and tachometer drives. On most piston engines the accessory end is the rear of the engine, opposite the propeller; on turbine engines it is typically the section housing the accessory gearbox.
Plain English
The part of the engine where bolt-on parts like pumps, magnetos, and generators are mounted and driven. It's the 'back' of the engine, opposite the propeller end.
Context Anchor
Seen in aircraft engine maintenance manuals, inspection write-ups, and discussions about where a component is mounted on a piston engine.
Derivation
Accessory' comes from the Latin accessorius, meaning 'something added or attached.' These components are 'added on' to the basic engine — the engine could run without them, but the aircraft systems they support could not.
Why Pilots Care
Knowing which end is the accessory end matters during inspections, troubleshooting, and component changes. Many of the items a pilot or technician checks during preflight or maintenance — magnetos, oil pump, fuel pump — live here.
Intuition Check
Do not read accessory as optional or unimportant here. On an aircraft engine, accessory end means the engine end where important support components are mounted and driven.
Example Sentence 1
The technician removed the cowling to access the magnetos mounted on the accessory end of the engine.
Example Sentence 2
All accessories must be removed from the accessory end prior to separating the crankcase halves.