Text in force at 25-153: from 25-40, effective 2 May 1977.
(a) Turbine engine operating characteristics must be investigated in flight to determine that no adverse characteristics (such as stall, surge, or flameout) are present, to a hazardous degree, during normal and emergency operation within the range of operation limitations of the airplane and of the engine.
[(b) [Reserved.]]
(c) The turbine engine air inlet system may not, as a result of air flow distortion during normal operation, cause vibration harmful to the engine.
42 FR 15043 · Source