§29.939 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 rotorcraft and of the engine. (b) The turbine en gine air in let system m ay not, as a resul t of airflow distortion during normal operation, cause vibration harmful to the engine. (c) For governor-cont rolled engi nes, i t must be shown that there exists no hazardous torsional instability o f th e d rive system associated with critical co mbinations o f p ower, rotational speed, and control displacement.