Pressure cross-feed arrangements

This regulation addresses fuel pressure cross-feed lines on Part 121 aircraft—the plumbing that allows fuel to be transferred between different tanks or fuel systems.

If these lines run through areas where people or cargo are located, the regulation requires one of two safety measures: either crewmembers must have a way to shut off fuel flow to those lines, or the lines must be enclosed in a fuel-proof and fume-proof housing that's ventilated and drains outside the aircraft. This prevents fuel leaks from endangering occupants or cargo.

Additionally, any fuel line section that can be isolated by valves on both ends must have a pressure relief system. This prevents dangerous pressure buildup if the trapped fuel heats up (such as from nearby hot components), which could otherwise rupture the line. These requirements reduce fire risk and protect against fuel system failures.

*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.*