14 CFR §27.1509

1. (a)Maximum power-off (autorotation). The maximum power-off rotor speed must be established so that it does not exceed 95 percent of the lesser of—
   1. (1)The maximum design r.p.m. determined under § 27.309(b); and
   2. (2)The maximum r.p.m. shown during the type tests.
2. (b)Minimum power off. The minimum power-off rotor speed must be established so that it is not less than 105 percent of the greater of—
   1. (1)The minimum shown during the type tests; and
   2. (2)The minimum determined by design substantiation.
3. (c)Minimum power on. The minimum power-on rotor speed must be established so that it is—
   1. (1)Not less than the greater of—
      1. (i)The minimum shown during the type tests; and
      2. (ii)The minimum determined by design substantiation; and
   2. (2)Not more than a value determined under § 27.33(a)(1) and (b)(1).