FAR 23.2435 — Induction and Exhaust Systems
FAR 23.2435 sets airworthiness rules for Part 23 airplane induction and exhaust systems, covering airflow, fire safety, foreign matter, and heat hazards.
In Plain English
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.
Regulation Text
14 CFR § 23.2435§ 23.2435 Powerplant induction and exhaust systems.
(a) The air induction system for each powerplant or auxiliary power unit and their accessories must—
(1) Supply the air required by that powerplant or auxiliary power unit and its accessories under likely operating conditions;
(2) Be designed to prevent likely hazards in the event of fire or backfire;
(3) Minimize the ingestion of foreign matter; and
(4) Provide an alternate intake if blockage of the primary intake is likely.
(b) The exhaust system, including exhaust heat exchangers for each powerplant or auxiliary power unit, must—
(1) Provide a means to safely discharge potential harmful material; and
(2) Be designed to prevent likely hazards from heat, corrosion, or blockage.
Oral Exam Questions a DPE Might Ask
Q1Why does your airplane have an alternate air or carb heat source?
FAR 23.2435 requires an alternate intake if the primary induction air source is likely to become blocked, protecting against issues like induction icing or filter clogging.
Q2What are the design requirements for an aircraft's exhaust system under Part 23?
Per FAR 23.2435(b), the exhaust system and any heat exchangers must safely discharge potentially harmful material and be designed to prevent hazards from heat, corrosion, or blockage.
Q3What hazards must the induction system design protect against?
FAR 23.2435(a) requires the induction system to supply adequate air, prevent hazards from fire or backfire, minimize foreign matter ingestion, and provide an alternate intake when primary blockage is likely.
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Related Sections in Part 23