Location of fuel tanks

This regulation establishes three safety requirements for where fuel tanks can be placed on Part 121 aircraft (commercial airliners).

First, fuel tank placement must follow the specifications in § 121.255, which addresses fire protection requirements. Second, the skin of the engine nacelle directly behind major engine air outlets cannot serve as a wall of an integral fuel tank—this prevents hot engine exhaust from heating fuel and creating fire hazards.

Third, fuel tanks must be separated from areas where people sit or work using enclosures that prevent both fuel vapors and liquid fuel from entering those spaces. This isolation protects passengers and crew from toxic fumes and reduces fire risk in the cabin.

These rules are fundamental to aircraft design and certification, ensuring fuel systems don't create fire or health hazards. Pilots won't interact with these requirements operationally, but they're critical to the safety of the aircraft they fly.

*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.*