Fire-extinguishing systems

This regulation requires Part 121 air carriers to install fire-extinguishing systems in all designated fire zones of their aircraft, unless they can demonstrate that fireproof materials alone provide equivalent protection against fire destroying the airplane. Fire zones are areas where fires are most likely to occur or spread, typically engine nacelles and auxiliary power unit compartments.

The rule also mandates that materials used in the fire-extinguishing system itself must be chemically compatible with the extinguishing agent. This prevents dangerous reactions that could create additional hazards during a fire emergency.

In practice, this means airlines must maintain functional fire suppression systems in critical aircraft areas. These systems—usually containing agents like Halon or newer alternatives—must be designed so their components won't break down or react when the extinguishing agent is discharged, ensuring the system works as intended when needed to protect the aircraft and occupants.

*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.*