Section 25.337 14 CFR Ch. I (1-1-19 Edition) case, the margin may not be reduced to less than 0.05M. (c) Design maneuvering speed VA. For VA, the following apply: (1) VA may not be less than VS1 - n where - (i) n is the limit positive maneuvering load factor at VC; and (ii) VS1 is the stalling speed with flaps retracted. (2) VA and VS must be evaluated at the design weight and altitude under consideration. (3) VA need not be more than VC or the speed at which the positive CN max curve intersects the positive maneuver load factor line, whichever is less. (d) Design speed for maximum gust intensity, VB. (1) VB may not be less than 12 - K g U ref Vc a - VS1 -1 + - 498w - - where - VS1 = the 1-g stalling speed based on CNAmax with the flaps retracted at the particular weight under consideration; Vc = design cruise speed (knots equivalent airspeed); Uref = the reference gust velocity (feet per second equivalent airspeed) from Section 25.341(a)(5)(i); w = average wing loading (pounds per square foot) at the particular weight under consideration. 5.3 + Section Section 25.337 Limit maneuvering load factors. 2w cag spaschal on DSK3GDR082PROD with CFR r = density of air (slugs/ft3); c = mean geometric chord of the wing (feet); g = acceleration due to gravity (ft/sec2); a = slope of the airplane normal force coefficient curve, CNA per radian; (2) At altitudes where VC is limited by Mach number - (i) VB may be chosen to provide an optimum margin between low and high speed buffet boundaries; and, (ii) VB need not be greater than VC. (e) Design flap speeds, VF. For VF, the following apply: (1) The design flap speed for each flap position (established in accordance with Section 25.697(a)) must be sufficiently (a) Except where limited by maximum (static) lift coefficients, the airplane is assumed to be subjected to symmetrical maneuvers resulting in the limit maneuvering load factors prescribed in this section. Pitching velocities appropriate to the corresponding pull-up and steady turn maneuvers must be taken into account. (b) The positive limit maneuvering load factor n for any speed up to Vn may not be less than 2.1 + 24,000/ (W + 10,000) except that n may not be less than 2.5 and need not be greater than 3.8 - where W is the design maximum takeoff weight. (c) The negative limit maneuvering load factor - 238 VerDate Sep<11>2014 12:50 Apr 30, 2019 Jkt 247046 PO 00000 Frm 00248 Fmt 8010 Sfmt 8010 Y:\SGML\247046.XXX 247046 ER09FE96.017 Section= .88 Section [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35 FR 5672, Apr. 8, 1970; Amdt. 25-86, 61 FR 5220, Feb. 9, 1996; Amdt. 25-91, 62 FR 40704, July 29, 1997] ER09fe96.016 Kg = greater than the operating speed recommended for the corresponding stage of flight (including balked landings) to allow for probable variations in control of airspeed and for transition from one flap position to another. (2) If an automatic flap positioning or load limiting device is used, the speeds and corresponding flap positions programmed or allowed by the device may be used. (3) VF may not be less than - (i) 1.6 VS1 with the flaps in takeoff position at maximum takeoff weight; (ii) 1.8 VS1 with the flaps in approach position at maximum landing weight, and (iii) 1.8 VS0 with the flaps in landing position at maximum landing weight. (f) Design drag device speeds, VDD. The selected design speed for each drag device must be sufficiently greater than the speed recommended for the operation of the device to allow for probable variations in speed control. For drag devices intended for use in high speed descents, VDD may not be less than VD. When an automatic drag device positioning or load limiting means is used, the speeds and corresponding drag device positions programmed or allowed by the automatic means must be used for design.