§27.45 General

(a) Unless otherwise prescribed, the performance requirements of this Subpart must be met for still air and a standard atmosphere. (b) The performance must correspond to the engine power available under the particular ambient atmospheric conditions, the particular flight condition, and the relative humidity specified in sub-paragraphs (d) or (e), as appropriate. (c) The available power must correspond to engine power, not exceeding the approved power, less: (1) Installation losses; and (2) The power absorbed by the accessories and services appropriate to the particular ambient atmospheric conditions and the particular flight condition. (d) For reciprocating engine-powered rotorcraft, the performance, as affected by engine power, must be based on a relative humidity of 80% in a standard atmosphere. (e) For turbine engine-powered rotorcraft, the performance, as affected by engine power, must be based on a relative humidity of: (1) 80%, at and below standard temperature; and (2) 34%, at and above standard temperature plus 28°C (50°F) between these two temperatures, the relative humidity must vary linearly. (f) For turbine engine-powered rotorcraft, a means must be provided to permit the pilot to determine prior to take-off that each engine is capable of developing the power necessary to achieve the applicable rotorcraft performance prescribed in this Subpart.