Text in force at 27-51: from 27-21, effective 6 Dec 1984.
[For rotorcraft with wheel-type landing gear, a braking device must be installed that is--]
(a) Controllable by the pilot;
(b) Usable during power-off landings; and
(c) Adequate to--
(1) Counteract any normal unbalanced torque when starting or stopping the rotor; and
(2) Hold the rotorcraft parked on a 10° slope on a dry, smooth pavement.
49 FR 44434 · Source