Fuel system lines and fittings

This regulation sets design and installation standards for fuel system lines and fittings on Part 121 aircraft. Fuel lines must be properly installed and supported to prevent excessive vibration and must be strong enough to handle fuel pressure and the stresses of flight maneuvers.

Where components may move relative to each other (like between the engine and airframe), fuel lines must have flexibility built in to accommodate that motion. When lines experience both pressure and axial (lengthwise) loading, they must use flexible hose assemblies rather than simple hose clamps, which could fail under these combined stresses.

All flexible hoses must be either an officially acceptable type or proven suitable through testing for their specific use. These requirements ensure fuel system integrity and prevent leaks or failures that could lead to fuel starvation, fire, or other serious safety hazards during flight operations.

*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.*