25.1517—Rough air speed, V RA .
A rough air speed, VRA, for use as the recommended turbulence penetration airspeed in § 25.1585(a)(8), must be established, which—
(3)
Is sufficiently less than VMO to ensure that likely speed variation during rough air encounters will not cause the overspeed warning to operate too frequently. In the absence of a rational investigation substantiating the use of other values, VRA must be less than VMO —35 knots (TAS).