FAR 23.2425 — Powerplant Operation

FAR 23.2425 is a Part 23 airworthiness standard that sets baseline requirements for how an airplane's powerplant (engine and related systems) must behave once installed. It applies to the airplane manufacturer during certification, but understanding it helps pilots appreciate what their engine is designed to do.

The rule has two main requirements:

• No hazardous characteristics: The installed powerplant must run safely throughout all normal and emergency operations, as long as the pilot stays within the published operating limitations for both the airplane and the engine. That means no unexpected stalls, surges, fires, or runaways when operated by the book.
• In-flight shutdown and restart capability: The pilot must be able to stop the engine in flight and then restart it within an established operational envelope (typically defined in the AFM as airspeed and altitude windows).

Operationally, this is why your POH/AFM contains an air-start procedure and engine limitations — they exist to keep you inside the envelope the manufacturer certified under this rule.