Definition
Valves located at the firewall of each engine that, when activated, stop the flow of fuel, oil, and hydraulic fluid from the airframe into the engine compartment. In multiengine airplanes they are typically operated from the cockpit as part of the engine securing or feathering procedure following an engine failure or fire.
Plain English
Cockpit-controlled valves that cut off fuel and other fluids running into a failed or burning engine, so those fluids cannot feed a fire or leak into the engine bay.
Context Anchor
Seen in engine-securing and emergency checklist discussions, especially after feathering a propeller on a multiengine airplane.
Derivation
The firewall is the fire-resistant barrier between the engine and the rest of the airframe. A shutoff valve simply closes off a flow. Together the term describes valves placed right at that barrier so fluids can be stopped before they cross into the engine compartment.
Why Pilots Care
Allows rapid isolation of the engine to prevent fire spread and supports safe engine shutdown without fluid leaks.
Intuition Check
Do not think of a computer firewall here. In this context, the firewall is the physical fire-resistant barrier near the engine, and the shutoff valves are real valves that stop fluid flow.
Example Sentence 1
After feathering the right propeller, the pilot closed the firewall shutoff valves to isolate the engine from fuel and oil.
Example Sentence 2
The checklist calls for closing the firewall shutoff valves before feathering the propeller on a failed engine.