Text in force at 25-153: from 25-108, effective 26 Dec 2002.
(a) Any short period oscillation, not including combined lateral-directional oscillations, occurring between [1.13 VSR] and maximum allowable speed appropriate to the configuration of the airplane must be heavily damped with the primary controls--
(1) Free; and
(2) In a fixed position.
(b) Any combined lateral-directional oscillations ("Dutch roll") occurring between [1.13 VSR] and maximum allowable speed appropriate to the configuration of the airplane must be positively damped with controls free, and must be controllable with normal use of the primary controls without requiring exceptional pilot skill.
67 FR 70827 · Source