Text in force at 29-59: from 29-0, effective 1 Feb 1965.
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.
29 FR 16150 · Source