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Federal Aviation Regulations

Sec. 25.253 — High-speed characteristics.

(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 airplane trimmed at any likely cruise speed up to V MO/ M MO.These conditions and characteristics include gust upsets, inadvertent control movements, low stick force gradient in relation to control friction, passenger movement, leveling off from climb, and descent from Mach to airspeed limit altitudes.

(2) Allowing for pilot reaction time after effective inherent or artificial speed warning occurs, it must be shown that the airplane can be recovered to a normal attitude and its speed reduced to V MO/ M MO,without—

(i) Exceptional piloting strength or skill;

(ii) Exceeding V D/ M D, V DF/ M DF,or the structural limitations; and

(iii) Buffeting that would impair the pilot's ability to read the instruments or control the airplane for recovery.

(3) With the airplane 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 airplane 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/MDFand there must be no sudden or excessive reduction of elevator control force as VDF/MDFis reached.

(b) Maximum speed for stability characteristics. VFC/MFC. VFC/MFCis the maximum speed at which the requirements of §§25.143(g), 25.147(e), 25.175(b)(1), 25.177, and 25.181 must be met with flaps and landing gear retracted. Except as noted in §25.253(c), VFC/MFCmay not be less than a speed midway between VMO/MMOand VDF/MDF, except that for altitudes where Mach number is the limiting factor, MFCneed 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 ice accretions defined in appendix C, at which the requirements of §§25.143(g), 25.147(e), 25.175(b)(1), 25.177, and 25.181 must be met, is the lower of:

(1) 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.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–23, 35 FR 5671, Apr. 8, 1970; Amdt. 25–54, 45 FR 60172, Sept. 11, 1980; Amdt. 25–72, 55 FR 29775, July 20, 1990; Amdt. 25–84, 60 FR 30750, June 9, 1995; Amdt. 25–121, 72 FR 44668, Aug. 8, 2007]

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