CS 27.653 Pressure venting and drainage of rotor blades
ED Decision 2003/15/RM
(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) Sub-paragraphs (a)(1) and (2) do not apply to sealed rotor blades capable of withstanding the maximum pressure differentials expected in service.
ED Decision 2003/15/RM
(a) The rotors and blades must be mass balanced as necessary to –
(1) Prevent excessive vibration; and
(2) Prevent flutter at any speed up to the maximum forward speed.
(b) The structural integrity of the mass balance installation must be substantiated.
CS 27.661 Rotor blade clearance
ED Decision 2003/15/RM
There must be enough clearance between the rotor blades and other parts of the structure to prevent the blades from striking any part of the structure during any operating condition.
CS 27.663 Ground resonance prevention means
ED Decision 2003/15/RM
(a) The reliability of the means for preventing ground resonance must be shown either by analysis and tests, or reliable service experience, or by showing through analysis or tests that malfunction or failure of a single means will not cause ground resonance.
(b) The probable range of variations, during service, of the damping action of the ground resonance prevention means must be established and must be investigated during the test required by CS 27.241.