CS 25.253 High-speed characteristics

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

CS 25.253 High-speed characteristics ED Decision 2016/010/R (a) *Speed increase and recovery characteristics.* The following speed increase and recovery characteristics must be met: (1) Operating conditions and characteristics likely to cause inadvertent speed increases (including upsets in pitch and roll) must be simulated with the aeroplane trimmed at any likely cruise speed up to VMO/MMO. These conditions and characteristics include gust upsets, inadvertent control movements, low stick force gradient in relation to control friction, passenger movement, levelling off from climb, and descent from Mach to air speed limit altitudes. (2) Allowing for pilot reaction time after effective inherent or artificial speed warning occurs, it must be shown that the aeroplane can be recovered to a normal attitude and its speed reduced to VMO/MMO, without – (i) Exceptional piloting strength or skill; (ii) Exceeding VD/MD, VDF/MDF, or the structural limitations; and (iii) Buffeting that would impair the pilot’s ability to read the instruments or control the aeroplane for recovery. (3) With the aeroplane trimmed at any speed up to VMO/MMO, there must be no reversal of the response to control input about any axis at any speed up to VDF/MDF. Any tendency to pitch, roll, or yaw must be mild and readily controllable, using normal piloting techniques. When the aeroplane is trimmed at VMO/MMO, the slope of the elevator control force versus speed curve need not be stable at speeds greater than VFC/MFC, but there must be a push force at all speeds up to VDF/MDF and there must be no sudden or excessive reduction of elevator control force as VDF/MDF is reached. (4) Adequate roll capability to assure a prompt recovery from a lateral upset condition must be available at any speed up to VDF/MDF. (See [AMC 25.253(a)(4)](#_DxCrossRefBm1709820889).) (5) *Extension of speedbrakes.* With the aeroplane trimmed at VMO/MMO, extension of the speedbrakes over the available range of movements of the pilots control, at all speeds above VMO/MMO, but not so high that VDF/MDF would be exceeded during the manoeuvre, must not result in: (i) An excessive positive load factor when the pilot does not take action to counteract the effects of extension; (ii) Buffeting that would impair the pilot’s ability to read the instruments or control the aeroplane for recovery; or (iii) A nose-down pitching moment, unless it is small. (See [AMC 25.253(a)(5)](#_DxCrossRefBm1709820888).) (6) Reserved (b) *Maximum speed for stability characteristics, VFC/MFC.* VFC/MFC is the maximum speed at which the requirements of [CS 25.143(g)](#_DxCrossRefBm1709820670), [25.147(f)](#_DxCrossRefBm1709820699), [25.175(b)(1)](#_DxCrossRefBm1709820695), [25.177(a)](#_DxCrossRefBm1709820694) through (c), and [25.181](#_DxCrossRefBm1709820693) must be met with wing-flaps and landing gear retracted. Except as noted in CS 25.253(c), VFC/MFC may not be less than a speed midway between VMO/MMO and VDF/MDF, except that, for altitudes where Mach Number is the limiting factor, MFC need not exceed the Mach Number at which effective speed warning occurs. (c) Maximum speed for stability characteristics in icing conditions. The maximum speed for stability characteristics with the most critical of the ice accretions defined in Appendices C and O, as applicable, in accordance with [CS 25.21(g)](#_DxCrossRefBm1709820660), at which the requirements of CS 25.143(g), 25.147(f), 25.175(b)(1), 25.177(a) through (c) and 25.181 must be met, is the lower of: (1) 556 km/h (300 knots) CAS, (2) VFC, or (3) A speed at which it is demonstrated that the airframe will be free of ice accretion due to the effects of increased dynamic pressure." [Amdt. 25/3] [Amdt 25/11] [Amdt 25/16] [Amdt 25/18]