Definition
A valve mounted at the firewall that, when closed, stops the flow of fuel, hydraulic fluid, or other flammable liquid from the airframe into the engine compartment. It is operated remotely from the cockpit and is used to isolate the engine from its fluid supply in the event of an engine fire or other emergency.
Plain English
A pilot-controlled valve that cuts off the flow of fuel or other flammable liquid into the engine area, usually pulled in an engine fire to starve the fire of fuel.
Context Anchor
Seen in aircraft fuel system descriptions, engine fire procedures, and maintenance checks around the engine firewall.
Derivation
The firewall is the fire-resistant barrier between the engine compartment and the rest of the aircraft. The valve is named for its location at this barrier, where it can sever the fluid supply right at the boundary so nothing flammable continues feeding the fire on the engine side.
Why Pilots Care
Provides an immediate way to isolate fuel and starve an engine fire or serious leak.
Intuition Check
Do not think of “firewall” as a computer term here. In this term, the firewall is the fire-resistant barrier behind the engine, and the valve shuts off fluid flow at that barrier.
Example Sentence 1
When the engine fire warning illuminated, the pilot pulled the fire handle, which closed the firewall shutoff valve and stopped fuel flow to the burning engine.
Example Sentence 2
On the preflight, the pilot confirmed the firewall shutoff valve handle was in the open position.