14 C.F.R. § 27.71
For single-engine helicopters and multiengine helicopters that do not meet the Category A engine isolation requirements of Part 29 of this chapter, the minimum rate of descent airspeed and the best angle-of-glide airspeed must be determined in autorotation at—
[Amdt. 27-21, 49 FR 44433, Nov. 6, 1984]