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					                                                              Federal Aviation Administration, DOT                                                                § 25.25

                                                                 (2) By systematic investigation of                     ditions, are allowed for flight in icing
                                                              each probable combination of weight                       conditions or with ice accretion.
                                                              and center of gravity, if compliance                      [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
                                                              cannot be reasonably inferred from                        amended by Amdt. 25–23, 35 FR 5671, Apr. 8,
                                                              combinations investigated.                                1970; Amdt. 25–42, 43 FR 2320, Jan. 16, 1978;
                                                                 (b) [Reserved]                                         Amdt. 25–72, 55 FR 29774, July 20, 1990; Amdt.
                                                                 (c) The controllability, stability,                    25–121, 72 FR 44665, Aug. 8, 2007]
                                                              trim, and stalling characteristics of
                                                                                                                        § 25.23     Load distribution limits.
                                                              the airplane must be shown for each al-
                                                              titude up to the maximum expected in                        (a) Ranges of weights and centers of
                                                              operation.                                                gravity within which the airplane may
                                                                 (d) Parameters critical for the test                   be safely operated must be established.
                                                              being conducted, such as weight, load-                    If a weight and center of gravity com-
                                                              ing (center of gravity and inertia), air-                 bination is allowable only within cer-
                                                              speed, power, and wind, must be main-                     tain load distribution limits (such as
                                                                                                                        spanwise) that could be inadvertently
                                                              tained within acceptable tolerances of
                                                                                                                        exceeded, these limits and the cor-
                                                              the critical values during flight test-
                                                                                                                        responding weight and center of grav-
                                                              ing.                                                      ity combinations must be established.
                                                                 (e) If compliance with the flight                        (b) The load distribution limits may
                                                              characteristics requirements is depend-                   not exceed—
                                                              ent upon a stability augmentation sys-                      (1) The selected limits;
                                                              tem or upon any other automatic or                          (2) The limits at which the structure
                                                              power-operated system, compliance                         is proven; or
                                                              must be shown with §§ 25.671 and 25.672.                    (3) The limits at which compliance
                                                                 (f) In meeting the requirements of                     with each applicable flight require-
                                                              §§ 25.105(d), 25.125, 25.233, and 25.237, the             ment of this subpart is shown.
                                                              wind velocity must be measured at a
                                                              height of 10 meters above the surface,                    § 25.25     Weight limits.
                                                              or corrected for the difference between                     (a) Maximum weights. Maximum
                                                              the height at which the wind velocity                     weights corresponding to the airplane
                                                              is measured and the 10-meter height.                      operating conditions (such as ramp,
                                                                 (g) The requirements of this subpart                   ground or water taxi, takeoff, en route,
                                                              associated with icing conditions apply                    and landing), environmental conditions
                                                              only if the applicant is seeking certifi-                 (such as altitude and temperature), and
                                                              cation for flight in icing conditions.                    loading conditions (such as zero fuel
                                                                 (1) Each requirement of this subpart,                  weight, center of gravity position and
                                                              except §§ 25.121(a), 25.123(c), 25.143(b)(1)              weight distribution) must be estab-
                                                              and (b)(2), 25.149, 25.201(c)(2), 25.207(c)               lished so that they are not more than—
                                                              and (d), 25.239, and 25.251(b) through (e),                 (1) The highest weight selected by
                                                              must be met in icing conditions. Com-                     the applicant for the particular condi-
                                                              pliance must be shown using the ice ac-                   tions; or
                                                              cretions defined in appendix C, assum-                      (2) The highest weight at which com-
                                                              ing normal operation of the airplane                      pliance with each applicable structural
                                                              and its ice protection system in accord-                  loading and flight requirement is
                                                              ance with the operating limitations                       shown, except that for airplanes
                                                              and operating procedures established                      equipped with standby power rocket
                                                                                                                        engines the maximum weight must not
                                                              by the applicant and provided in the
                                                                                                                        be more than the highest weight estab-
                                                              Airplane Flight Manual.
                                                                                                                        lished in accordance with appendix E of
                                                                 (2) No changes in the load distribu-                   this part; or
                                                              tion limits of § 25.23, the weight limits                   (3) The highest weight at which com-
                                                              of § 25.25 (except where limited by per-                  pliance is shown with the certification
                                                              formance requirements of this sub-                        requirements of Part 36 of this chapter.
                                                              part), and the center of gravity limits                     (b) Minimum weight. The minimum
                                                              of § 25.27, from those for non-icing con-                 weight (the lowest weight at which
                                                                                                                        compliance with each applicable re-
                                                                                                                        quirement of this part is shown) must
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                                                              § 25.27                                                                 14 CFR Ch. I (1–1–09 Edition)

                                                              be established so that it is not less                     § 25.33 Propeller speed and pitch lim-
                                                              than—                                                          its.
                                                                (1) The lowest weight selected by the                     (a) The propeller speed and pitch
                                                              applicant;                                                must be limited to values that will en-
                                                                (2) The design minimum weight (the                      sure–
                                                              lowest weight at which compliance                           (1) Safe operation under normal oper-
                                                              with each structural loading condition                    ating conditions; and
                                                              of this part is shown); or                                  (2) Compliance with the performance
                                                                (3) The lowest weight at which com-                     requirements of §§ 25.101 through 25.125.
                                                              pliance with each applicable flight re-                     (b) There must be a propeller speed
                                                              quirement is shown.                                       limiting means at the governor. It
                                                              [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as            must limit the maximum possible gov-
                                                              amended by Amdt. 25–23, 35 FR 5671, Apr. 8,               erned engine speed to a value not ex-
                                                              1970; Amdt. 25–63, 53 FR 16365, May 6, 1988]              ceeding the maximum allowable r.p.m.
                                                                                                                          (c) The means used to limit the low
                                                              § 25.27    Center of gravity limits.                      pitch position of the propeller blades
                                                                The extreme forward and the extreme                     must be set so that the engine does not
                                                              aft center of gravity limitations must                    exceed 103 percent of the maximum al-
                                                              be established for each practicably sep-                  lowable engine rpm or 99 percent of an
                                                              arable operating condition. No such                       approved maximum overspeed, which-
                                                              limit may lie beyond—                                     ever is greater, with—
                                                                (a) The extremes selected by the ap-                      (1) The propeller blades at the low
                                                              plicant;                                                  pitch limit and governor inoperative;
                                                                (b) The extremes within which the                         (2) The airplane stationary under
                                                              structure is proven; or                                   standard atmospheric conditions with
                                                                (c) The extremes within which com-                      no wind; and
                                                              pliance with each applicable flight re-                     (3) The engines operating at the take-
                                                              quirement is shown.                                       off manifold pressure limit for recipro-
                                                                                                                        cating engine powered airplanes or the
                                                              § 25.29 Empty     weight     and                cor-      maximum takeoff torque limit for tur-
                                                                   responding center of gravity.                        bopropeller engine-powered airplanes.
                                                                 (a) The empty weight and cor-                          [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
                                                              responding center of gravity must be                      amended by Amdt. 25–57, 49 FR 6848, Feb. 23,
                                                              determined by weighing the airplane                       1984; Amdt. 25–72, 55 FR 29774, July 20, 1990]
                                                              with—
                                                                 (1) Fixed ballast;                                                      PERFORMANCE
                                                                 (2) Unusable fuel determined under
                                                              § 25.959; and                                             § 25.101    General.
                                                                 (3) Full operating fluids, including—                    (a) Unless otherwise prescribed, air-
                                                                 (i) Oil;                                               planes must meet the applicable per-
                                                                 (ii) Hydraulic fluid; and                              formance requirements of this subpart
                                                                 (iii) Other fluids required for normal                 for ambient atmospheric conditions
                                                              operation of airplane systems, except                     and still air.
                                                              potable water, lavatory precharge                           (b) The performance, as affected by
                                                              water, and fluids intended for injection                  engine power or thrust, must be based
                                                              in the engine.                                            on the following relative humidities;
                                                                 (b) The condition of the airplane at                     (1) For turbine engine powered air-
                                                              the time of determining empty weight                      planes, a relative humidity of—
                                                              must be one that is well defined and                        (i) 80 percent, at and below standard
                                                              can be easily repeated.                                   temperatures; and
                                                              [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as              (ii) 34 percent, at and above standard
                                                              amended by Amdt. 25–42, 43 FR 2320, Jan. 16,              temperatures plus 50 °F.
                                                              1978; Amdt. 25–72, 55 FR 29774, July 20, 1990]            Between these two temperatures, the
                                                                                                                        relative humidity must vary linearly.
                                                              § 25.31    Removable ballast.                               (2) For reciprocating engine powered
                                                                Removable ballast may be used on                        airplanes, a relative humidity of 80 per-
                                                              showing compliance with the flight re-                    cent in a standard atmosphere. Engine
                                                              quirements of this subpart.                               power corrections for vapor pressure
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