Definition
A small colored disc fitted to the outside of a fire extinguisher container or pressurized system on an aircraft that ruptures and is blown out (or changes color) when the contents have been discharged. Its absence or rupture provides a visible external indication that the bottle has been fired or has released its charge.
Plain English
A little disc on the outside of a fire-extinguisher bottle that pops out or breaks when the bottle has been emptied. If the disc is missing or broken, you can tell at a glance that the bottle has gone off.
Context Anchor
Seen during aircraft preflight or maintenance checks of built-in fire-extinguishing systems, often on the outside of the aircraft near a discharge outlet.
Derivation
‘Discharge’ comes from Old French descharger, meaning to unload or release. Here it refers to the bottle releasing its contents. ‘Indicator’ simply means something that shows a condition. Together: a disc that shows whether the bottle has released its load.
Why Pilots Care
Reveals possible battery damage that could lead to electrical system failure in flight if left unaddressed.
Intuition Check
Do not read “discharge” here as an electrical spark. Here it means the release of fire-extinguishing gas or chemical from its bottle.
Example Sentence 1
On preflight, the pilot checked the discharge indicator disc on the engine fire bottle to confirm the system was still charged.
Example Sentence 2
A popped discharge indicator disc meant the battery required removal and bench charging before the next flight.