Definition
A small explosive or pyrotechnic device used to initiate the discharge of a fire extinguishing agent or other system on an aircraft. When triggered electrically, the squib ruptures a sealing disc or activates a charge that releases the contents of a pressurized container, such as a fire bottle in an engine or APU fire suppression system.
Plain English
A small electrical igniter that fires a tiny charge to break a seal and release something — usually the fire-extinguishing agent inside a pressurized bottle.
Context Anchor
Seen in aircraft maintenance instructions for fire-extinguishing systems and other emergency-release equipment.
Derivation
Squib originally meant a small firework or minor explosive charge. The aviation use keeps that core idea: a tiny, controlled explosive that does one specific job — in this case, breaking a seal so an extinguishing agent can flow.
Why Pilots Care
Pressing the fire handle or discharge button sends current to the squib, which is what actually releases the agent into the engine or compartment. If the squib fails or its electrical circuit is broken, the bottle will not discharge even though the system looks armed.
Grounding Statement
The squib is the trigger charge, not the whole fire bottle or emergency system.
Intuition Check
Do not think of a squib as the fire-extinguishing bottle itself. The squib is the small firing device that starts the bottle discharging.
Example Sentence 1
When the pilot pressed the engine fire bottle discharge switch, the squib fired and released the extinguishing agent into the engine nacelle.
Example Sentence 2
Continuity testing confirmed the squib circuit would fire when the cockpit switch was selected.