FAR 23.2435 — Induction and Exhaust Systems

FAR 23.2435 is a Part 23 airworthiness standard that tells designers how the air induction and exhaust systems of normal-category airplane engines and APUs must be built. It's not a rule pilots follow in flight, but understanding it helps you appreciate why your airplane has things like alternate air sources and shielded exhaust components.

For the induction system, the design must:

• Supply enough air to the engine/APU and accessories under expected operating conditions
• Prevent hazards from fire or backfire
• Minimize foreign matter ingestion (dirt, debris, ice)
• Provide an alternate intake if blockage of the primary is likely (this is why your aircraft has alternate air or carburetor heat)

For the exhaust system, including any heat exchangers, the design must:

• Safely discharge harmful material (hot gases, carbon monoxide)
• Prevent hazards from heat, corrosion, or blockage

Operationally, this is why exhaust leaks are a big deal — a cracked muffler or heat exchanger can dump CO into the cabin through the heater.