CS 25.177 Static directional and lateral stability

• ED Decision 2016/010/R found in: CS-25 Amdt 27 - Large Aeroplanes (Jan 2023)

CS 25.177 Static directional and lateral stability ED Decision 2016/010/R (See AMC 25.177) (a) The static directional stability (as shown by the tendency to recover from a skid with the rudder free) must be positive for any landing gear and flap position and symmetrical power condition, at speeds from 1·13 VSR1, up to VFE, VLE, or VFC/MFC (as appropriate). (b) The static lateral stability (as shown by the tendency to raise the low wing in a sideslip with the aileron controls free) for any landing gear and wingflap position and symmetric power condition, may not be negative at any airspeed (except that speeds higher than VFE need not be considered for wingflaps extended configurations nor speeds higher than VLE for landing gear extended configurations) in the following airspeed ranges: (1) From 1·13 VSR1 to VMO/MMO.. (2) From VMO/MMO to VFC/MFC, unless the divergence is – (i) Gradual; (ii) Easily recognisable by the pilot; and (iii) Easily controllable by the pilot (c) In straight, steady, sideslips over the range of sideslip angles appropriate to the operation of the aeroplane, the aileron and rudder control movements and forces must be substantially proportional to the angle of sideslip in a stable sense. The factor of proportionality must lie between limits found necessary for safe operation. The range of sideslip angles evaluated must include those sideslip angles resulting from the lesser of: (1) one-half of the available rudder control input; and (2) a rudder control force of 180 pounds. This requirement must be met for the configurations and speeds specified in sub-paragraph (a) of this paragraph. (See [AMC 25.177(c)](#_DxCrossRefBm1709820852).) (d) For sideslip angles greater than those prescribed by sub-paragraph (c) of this paragraph, up to the angle at which full rudder control is used or a rudder control force of 801 N (180 lbf) is obtained, the rudder control forces may not reverse, and increased rudder deflection must be needed for increased angles of sideslip. Compliance with this requirement must be shown using straight, steady sideslips, unless full lateral control input is achieved before reaching either full rudder control input or a rudder control force of 801 N (180 lbf) ; a straight, steady sideslip need not be maintained after achieving full lateral control input. This requirement must be met at all approved landing gear and wingflap positions for the range of operating speeds and power conditions appropriate to each landing gear and wing-flap position with all engines operating. (See [AMC 25.177(d)](#_DxCrossRefBm1709820851).) [Amdt 25/11] [Amdt 25/18]