ED Decision 2003/18/RM
(a) Vertical tail surfaces must be designed to withstand, in unaccelerated flight at speed VC, lateral gusts of the values prescribed for VC in CS-VLA 333(c).
(b) In the absence of a more rational analysis, the gust load must be computed as follows:
where -
Lvt = vertical tail loads (daN);
Kgt = 
= gust alleviation factor;
µgt = 
= lateral mass ratio;
Ude = derived gust velocities (m/s);
ρ = air density (kg/m3);
M = aeroplane mass (kg);
Svt = area of vertical tail (m2);
C̅t = mean geometric chord of vertical surface (m);
avt = lift curve slope of vertical tail (per radian);
K = radius of gyration in yaw (m);
lt = distance from aeroplane c.g. to lift centre of vertical surface (m);
g = acceleration due to gravity (m/s2); and
V = aeroplane equivalent speed (m/s).
(c) The average loading in figure B5 and the distribution in figure B8 of Appendix B may be used.