(b) The turbine engine air inlet system may not, as a result of airflow distortion during normal operation, cause vibration harmful to the engine.
(c) For governor-controlled engines, it must be shown that there exists no hazardous torsional instability of the drive system associated with critical combinations of power, rotational speed, and control displacement.
[Amdt. 29–2, 32 FR 6914, May 5, 1967, as amended by Amdt. 29–12, 41 FR 55473, Dec. 20, 1976]