Fire walls

This regulation requires that anything on the airplane that burns fuel or creates combustion during flight must be physically separated from the rest of the aircraft. This includes engines, auxiliary power units (APUs), fuel-burning heaters, and similar equipment.

The separation must be accomplished using firewalls, shrouds, or other equivalent barriers that prevent fire from spreading to other parts of the airplane. The key purpose is fire containment—if a fire starts in an engine or combustion equipment, these barriers are designed to keep it isolated and prevent it from reaching fuel tanks, passenger compartments, or critical flight systems.

This is a fundamental safety requirement for Part 121 air carrier operations. It ensures that even if combustion equipment malfunctions or catches fire, the crew has time to respond and the fire won't immediately threaten the entire aircraft.

*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.*