Lines and fittings

This regulation sets fire safety standards for lines and fittings in Part 121 aircraft, with requirements based on their location and function.

Lines located in designated fire zones must be flexible and fire-resistant with fire-resistant ends if they:

• Carry flammable fluids or gases under pressure
• Attach directly to the engine
• Experience relative motion between components

This flexibility requirement doesn't apply to lines that are integral parts of the engine itself.

Lines and fittings that don't experience pressure or relative motion between components have a simpler requirement—they must simply be made of fire-resistant materials, but don't need to be flexible.

In practice, this means fuel lines, hydraulic lines, and pneumatic lines in fire zones need both fire resistance and flexibility to withstand engine vibration and thermal expansion while minimizing fire risk. Static lines in these areas need only fire-resistant materials. These requirements help contain fires and prevent them from spreading through failed lines.

*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.*