Vent and drain lines

This regulation addresses vent and drain lines located in designated fire zones (areas where fires are most likely to occur, such as engine compartments). If these lines carry flammable fluids or gases, they must meet the same fire-resistant standards as fuel lines under § 121.259—but only when the FAA determines their rupture or breakage could create a fire hazard.

In practice, this means airlines operating under Part 121 must ensure that vent and drain lines in fire zones are constructed and installed to minimize fire risk if they fail. The regulation recognizes that not all vent and drain lines pose equal danger; the FAA evaluates each situation to determine which lines require enhanced fire protection. This prevents flammable vapors or liquids from feeding a fire if a line breaks during an engine fire or other high-temperature event, helping contain fires to their origin point and protecting the aircraft structure.

*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.*