Fuel system independence

This regulation requires that Part 121 air carrier fuel systems be designed with redundancy so that if any single component fails, you won't lose power to more than one engine. This means the fuel system must have sufficient independence between engines—if a fuel pump, valve, or line fails, only one engine should be affected, allowing the others to continue operating normally.

The rule doesn't mandate a completely separate fuel tank for each engine, though. Airlines can use alternative designs as long as they demonstrate these provide equivalent safety. For example, crossfeed systems with proper isolation valves or other protective features may be acceptable.

This matters because it ensures multi-engine aircraft maintain some engine power even after a fuel system failure, providing crucial redundancy for safe flight operations. It's a fundamental safety requirement that influences how aircraft fuel systems are designed and certified for airline service.

*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.*