CFR /  Title 14  /  Part 25  /  Sec. 25.1101 Carburetor air preheater design.

Each carburetor air preheater must be designed and constructed to--

(a) Ensure ventilation of the preheater when the engine is operated in cold air;

(b) Allow inspection of the exhaust manifold parts that it surrounds; and

(c) Allow inspection of critical parts of the preheater itself.