14 CFR § 25.399
Dual control system
July 13, 2020
(a) Each dual control system must be designed for the pilots operating in opposition, using individual pilot forces not less than—
(1) 0.75 times those obtained under §25.395; or
(2) The minimum forces specified in §25.397(c).
(b) The control system must be designed for pilot forces applied in the same direction, using individual pilot forces not less than 0.75 times those obtained under §25.395.