14 C.F.R. § 121.251 Engine accessory section diaphragm.
Title 14 - Aeronautics and Space
Unless equivalent protection can be shown by other means, a diaphragm that complies with §121.247 must be provided on air-cooled engines to isolate the engine power section and all parts of the exhaust system from the engine accessory compartment.
Title 14: Aeronautics and Space
PART 121—OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL OPERATIONS
Subpart J—Special Airworthiness Requirements
§ 121.251 Engine accessory section diaphragm.
