Text in force at 29-59: from 29-3, effective 25 Feb 1968.
[(a) For each rotor blade--
(1) There must be means for venting the internal pressure of the blade;
(2) Drainage holes must be provided for the blade; and
(3) The blade must be designed to prevent water from becoming trapped in it.
(b) Paragraph (a)(1) and (2) of this section does not apply to sealed rotor blades capable of withstanding the maximum pressure differentials expected in service.]
33 FR 967 · Source