Section 25.307

14 CFR Ch. I (1-1-19 Edition)

that might occur in any likely operating condition up to VD/MD, including
stall and probable inadvertent excursions beyond the boundaries of the buffet onset envelope. This must be shown
by analysis, flight tests, or other tests
found necessary by the Administrator.
(f) Unless shown to be extremely improbable, the airplane must be designed
to withstand any forced structural vibration resulting from any failure,
malfunction or adverse condition in
the flight control system. These must
be considered limit loads and must be
investigated at airspeeds up to VC/MC.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5672, Apr. 8,
1970; Amdt. 25-54, 45 FR 60172, Sept. 11, 1980;
Amdt. 25-77, 57 FR 28949, June 29, 1992; Amdt.
25-86, 61 FR 5220, Feb. 9, 1996]

Section 25.307 Proof of structure.
(a) Compliance with the strength and
deformation requirements of this subpart must be shown for each critical
loading condition. Structural analysis
may be used only if the structure conforms to that for which experience has
shown this method to be reliable. In
other cases, substantiating tests must
be made to load levels that are sufficient to verify structural behavior up
to loads specified in Section 25.305.
(b)-(c) [Reserved]
(d) When static or dynamic tests are
used to show compliance with the requirements of Section 25.305(b) for flight
structures, appropriate material correction factors must be applied to the
test results, unless the structure, or
part thereof, being tested has features
such that a number of elements contribute to the total strength of the
structure and the failure of one element results in the redistribution of
the load through alternate load paths.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5672, Apr. 8,
1970; Amdt. 25-54, 45 FR 60172, Sept. 11, 1980;
Amdt. 25-72, 55 FR 29775, July 20, 1990; 79 FR
59429, Oct. 2, 2014]

spaschal on DSK3GDR082PROD with CFR

FLIGHT LOADS
Section 25.321 General.
(a) Flight load factors represent the
ratio of the aerodynamic force component (acting normal to the assumed
longitudinal axis of the airplane) to the

weight of the airplane. A positive load
factor is one in which the aerodynamic
force acts upward with respect to the
airplane.
(b) Considering compressibility effects at each speed, compliance with
the flight load requirements of this
subpart must be shown - 
(1) At each critical altitude within
the range of altitudes selected by the
applicant;
(2) At each weight from the design
minimum weight to the design maximum weight appropriate to each particular flight load condition; and
(3) For each required altitude and
weight, for any practicable distribution
of disposable load within the operating
limitations recorded in the Airplane
Flight Manual.
(c) Enough points on and within the
boundaries of the design envelope must
be investigated to ensure that the maximum load for each part of the airplane
structure is obtained.
(d) The significant forces acting on
the airplane must be placed in equilibrium in a rational or conservative
manner. The linear inertia forces must
be considered in equilibrium with the
thrust and all aerodynamic loads,
while the angular (pitching) inertia
forces must be considered in equilibrium with thrust and all aerodynamic moments, including moments
due to loads on components such as
tail surfaces and nacelles. Critical
thrust values in the range from zero to
maximum continuous thrust must be
considered.
[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]

FLIGHT MANEUVER AND GUST
CONDITIONS
Section 25.331 Symmetric maneuvering conditions.
(a) Procedure. For the analysis of the
maneuvering flight conditions specified
in paragraphs (b) and (c) of this section, the following provisions apply:
(1) Where sudden displacement of a
control is specified, the assumed rate
of control surface displacement may
not be less than the rate that could be
applied by the pilot through the control system.

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