25.939—Turbine engine operating characteristics.
(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 operating limitations of the airplane and of the engine.
(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.