Flammable fluids

This regulation governs where flammable fluid tanks and reservoirs can be located on Part 121 aircraft. Generally, you cannot place tanks containing flammable fluids or gases in designated fire zones (areas where fires are most likely to occur, like engine compartments). However, there's an exception: if the entire system—including the fluid type, tank design, materials, shutoff mechanisms, and all connections—provides "equivalent safety," the tank may be located in a fire zone.

Additionally, any tank or reservoir must maintain at least half an inch of clear airspace between itself and any firewall or shroud that separates a designated fire zone. This spacing helps prevent heat transfer and provides a safety buffer.

These requirements matter because they reduce the risk of flammable fluids igniting during an engine or equipment fire, which could turn a contained fire into a catastrophic event. The rules balance operational necessity with fire safety through either physical separation or equivalent protective measures.

*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.*