Engine breather lines

Engine breather lines vent pressure and gases from aircraft engines, but they must be designed with specific safety considerations. The lines must be arranged so condensed water vapor can't collect and freeze anywhere along the route, which could block the line and cause pressure buildup.

The discharge point matters for two safety reasons: it must be located where any oil foam that emerges won't create a fire hazard, and where oil spray won't hit the pilots' windshield and obstruct their vision during flight.

Finally, breather lines cannot discharge into the engine's air induction system. This prevents oil vapors and contaminants from being drawn back into the engine, which could affect combustion and engine performance.

These requirements ensure breather systems work reliably without creating fire hazards, visibility problems, or engine contamination issues—critical for the multi-engine transport aircraft operating under Part 121.

*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.*