14 CFR § 29.45

The performance prescribed in this subpart must be determined—

With normal piloting skill and;

Without exceptionally favorable conditions.

Compliance with the performance requirements of this subpart must be shown—

For still air at sea level with a standard atmosphere and;

For the approved range of atmospheric variables.

The available power must correspond to engine power, not exceeding the approved power, less—

Installation losses; and

The power absorbed by the accessories and services at the values for which certification is requested and approved.

For reciprocating engine-powered rotorcraft, the performance, as affected by engine power, must be based on a relative humidity of 80 percent in a standard atmosphere.

For turbine engine-powered rotorcraft, the performance, as affected by engine power, must be based on a relative humidity of—

80 percent, at and below standard temperature; and

34 percent, at and above standard temperature plus 50 °F.

For turbine-engine-power rotorcraft, a means must be provided to permit the pilot to determine prior to takeoff that each engine is capable of developing the power necessary to achieve the applicable rotorcraft performance prescribed in this subpart.