Fire-extinguishing system materials

This regulation sets material standards for fire-extinguishing systems installed in designated fire zones of Part 121 aircraft.

The general rule requires all fire-extinguishing system components within fire zones to be made of fireproof materials—meaning they can withstand fire exposure without failing or burning through.

However, there's an important exception: connections between components that must move relative to each other (like flexible hoses or joints that accommodate aircraft flexing) only need to be fire-resistant rather than fully fireproof. Fire-resistant materials can withstand heat and flame for a limited time but aren't required to be completely impervious. These flexible connections must also be positioned to reduce the chance of mechanical failure.

This matters because fire-extinguishing systems must remain functional during the very fire they're designed to fight. If the system's own components burned through or failed when exposed to flames, it couldn't deliver extinguishing agent where needed. The flexibility exception recognizes that some movement is necessary while still maintaining reasonable fire protection.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*