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.
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14 CFR · PART 121
§ 121.251 Engine accessory section diaphragm.
Official text · Current as of Oct 19, 2026 · from eCFR
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