CS 25.175 Demonstration of static longitudinal stability

• ED Decision 2003/2/RM found in: CS-25 Amdt 27 - Large Aeroplanes (Jan 2023)

CS 25.175 Demonstration of static longitudinal stability ED Decision 2003/2/RM Static longitudinal stability must be shown as follows: (a) *Climb*. The stick force curve must have a stable slope at speeds between 85% and 115% of the speed at which the aeroplane – (1) Is trimmed with – (i) Wing-flaps retracted; (ii) Landing gear retracted; (iii) Maximum take-off weight; and (iv) The maximum power or thrust selected by the applicant as an operating limitation for use during climb; and (2) Is trimmed at the speed for best rate-of-climb except that the speed need not be less than 1·3 VSR1. (b) *Cruise*. Static longitudinal stability must be shown in the cruise condition as follows: (1) With the landing gear retracted at high speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15% of the trim speed plus the resulting free return speed range, or 93 km/h (50 kt) plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1·3 VSR1 nor speeds greater than VFC/MFC, nor speeds that require a stick force of more than 222 N (50 lbf)), with – (i) The wing-flaps retracted; (ii) The centre of gravity in the most adverse position (see [CS 25.27](#_DxCrossRefBm1709820661)); (iii) The most critical weight between the maximum take-off and maximum landing weights; (iv) The maximum cruising power selected by the applicant as an operating limitation (see [CS 25.1521](#_DxCrossRefBm1709820849)), except that the power need not exceed that required at VMO/MMO; and (v) The aeroplane trimmed for level flight with the power required in sub-paragraph (iv) above. (2) With the landing gear retracted at low speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15% of the trim speed plus the resulting free return speed range, or 93 km/h (50 kt) plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1·3 VSR1 nor speeds greater than the minimum speed of the applicable speed range prescribed in subparagraph (b)(1) of this paragraph, nor speeds that require a stick force of more than 222 N (50 lbf)), with – (i) Wing-flaps, centre of gravity position, and weight as specified in sub-paragraph (1) of this paragraph; (ii) Power required for level flight at a speed equal to  ; and (iii) The aeroplane trimmed for level flight with the power required in sub-paragraph (ii) above. (3) With the landing gear extended, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15% of the trim speed plus the resulting free return speed range or 93 km/h (50 kt) plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1·3 VSR1, nor speeds greater than VLE, nor speeds that require a stick force of more than 222 N (50 lbf)), with – (i) Wing-flap, centre of gravity position, and weight as specified in sub-paragraph (b)(1) of this paragraph; (ii) The maximum cruising power selected by the applicant as an operating limitation, except that the power need not exceed that required for level flight at VLE; and (iii) The aeroplane trimmed for level flight with the power required in sub-paragraph (ii) above. (c) *Approach.* The stick force curve must have a stable slope at speeds between VSW, and 1·7 VSR1 with – (1) Wing-flaps in the approach position; (2) Landing gear retracted; (3) Maximum landing weight; and (4) The aeroplane trimmed at 1·3 VSR1, with enough power to maintain level flight at this speed. (d) *Landing*. The stick force curve must have a stable slope and the stick force may not exceed 356 N (80 lbf) at speeds between VSW, and 1·7 VSR0 with – (1) Wing-flaps in the landing position; (2) Landing gear extended; (3) Maximum landing weight; (4) The aeroplane trimmed at 1·3 VSR0 with – (i) Power or thrust off, and (ii) Power or thrust for level flight.