14 CFR § 25.337 - Limit maneuvering load factors.
(a) Except where limited by maximum (static) lift coefficients, the airplane is assumed to be subjected to symmetrical maneuvers resulting in the limit maneuvering load factors prescribed in this section. Pitching velocities appropriate to the corresponding pull-up and steady turn maneuvers must be taken into account.
(b) The positive limit maneuvering load factor n for any speed up to Vn may not be less than 2.1 + 24,000/ (W + 10,000) except that n may not be less than 2.5 and need not be greater than 3.8 - where W is the design maximum takeoff weight.
(c) The negative limit maneuvering load factor -
(1) May not be less than −1.0 at speeds up to VC; and
(2) Must vary linearly with speed from the value at VC to zero at VD.