Definition
The fixed, non-rotating plate in a multiple-disc brake assembly that anchors the stack of brake discs and provides the reaction surface against which the pressure plate squeezes them when the brakes are applied.
Plain English
It is the solid backing plate at one end of the brake stack. The brake discs press against it when you push the brake pedals, which is what creates the friction that slows the wheel.
Context Anchor
Seen in aircraft brake diagrams, maintenance manuals, and brake inspection discussions around the wheel assembly.
Derivation
From 'back' (the rear or anchoring side) and 'plate' (a flat, rigid piece). The name simply describes its job: the plate at the back of the brake stack that everything else pushes against.
Why Pilots Care
A damaged or worn brake back plate reduces braking effectiveness and can lead to uneven wear or complete brake failure.
Analogy
Think of squeezing a stack of papers between your two hands. The back plate is the hand that stays still while the other hand presses the stack against it.
Intuition Check
Do not think of the brake back plate as just a rear cover. In this context, it is a fixed support part that helps the brake apply force correctly.
Example Sentence 1
During the brake inspection, the mechanic checked the back plate for cracks and uneven wear before reassembling the wheel.
Example Sentence 2
Replacement of the brake back plate was needed after the linings had worn through to the metal.