**Sec. 25.427 - Unsymmetrical loads.**
(a) In designing the airplane for
lateral gust, yaw maneuver and roll maneuver conditions, account must be
taken of unsymmetrical loads on the empennage arising from effects such as
slipstream and aerodynamic interference with the wing, vertical fin and
other aerodynamic surfaces.

(b) The horizontal tail must be assumed
to be subjected to unsymmetrical loading conditions determined as follows:

(1) 100 percent of the maximum loading
from the symmetrical maneuver conditions of §25.331 and the vertical gust
conditions of §25.341(a) acting separately on the surface on one side of
the plane of symmetry; and

(2) 80 percent of these loadings acting
on the other side.

(c) For empennage arrangements where the
horizontal tail surfaces have dihedral angles greater than plus or minus
10 degrees, or are supported by the vertical tail surfaces, the surfaces
and the supporting structure must be designed for gust velocities
specified in §25.341(a) acting in any orientation at right angles to the
flight path.

(d) Unsymmetrical loading on the
empennage arising from buffet conditions of §25.305(e) must be taken into
account.

[Doc. No. 27902, 61 FR 5222, Feb. 9, 1996]