Federal Aviation Administration, DOT

Section 25.345

for the maximum response at the nacelle center of gravity derived from the
following dynamic gust conditions applied to the airplane:
(1) A discrete gust determined in accordance with Section 25.341(a) at each angle
normal to the flight path, and separately,
(2) A pair of discrete gusts, one
vertical and one lateral. The length of
each of these gusts must be independ-

ently tuned to the maximum response
in accordance with Section 25.341(a). The penetration of the airplane in the combined
gust field and the phasing of the
vertical and lateral component gusts
must be established to develop the
maximum response to the gust pair. In
the absence of a more rational analysis, the following formula must be
used for each of the maximum engine
loads in all six degrees of freedom:

Where - 
PL = limit load;
PL-1g = steady 1g load for the condition;
LV = peak incremental response load due to
a vertical gust according to Section 25.341(a);
and
LL = peak incremental response load due to
a lateral gust according to Section 25.341(a).

design condition of paragraph (b)(1) of
this section; and
(3) The flutter, deformation, and vibration requirements must also be met
with zero fuel.

Section 25.343 Design fuel and oil loads.
(a) The disposable load combinations
must include each fuel and oil load in
the range from zero fuel and oil to the
selected maximum fuel and oil load. A
structural reserve fuel condition, not
exceeding 45 minutes of fuel under the
operating conditions in Section 25.1001(e) and
(f), as applicable, may be selected.
(b) If a structural reserve fuel condition is selected, it must be used as the
minimum fuel weight condition for
showing compliance with the flight
load requirements as prescribed in this
subpart. In addition - 
(1) The structure must be designed
for a condition of zero fuel and oil in
the wing at limit loads corresponding
to - 
(i) A maneuvering load factor of +
2.25; and
(ii) The gust and turbulence conditions of Section 25.341(a) and (b), but assuming
85% of the gust velocities prescribed in
Section 25.341(a)(4) and 85% of the turbulence
intensities prescribed in Section 25.341(b)(3).
(2) Fatigue evaluation of the structure must account for any increase in
operating stresses resulting from the

Section 25.345 High lift devices.
(a) If wing flaps are to be used during
takeoff, approach, or landing, at the
design flap speeds established for these
stages of flight under Section 25.335(e) and
with the wing flaps in the corresponding positions, the airplane is
assumed to be subjected to symmetrical maneuvers and gusts. The resulting limit loads must correspond to the
conditions determined as follows:
(1) Maneuvering to a positive limit
load factor of 2.0; and
(2) Positive and negative gusts of 25
ft/sec EAS acting normal to the flight
path in level flight. Gust loads resulting on each part of the structure must
be determined by rational analysis.
The analysis must take into account
the unsteady aerodynamic characteristics and rigid body motions of the aircraft. The shape of the gust must be as
described in Section 25.341(a)(2) except that - 
Uds = 25 ft/sec EAS;
H = 12.5 c; and
c = mean geometric chord of the wing (feet).

(b) The airplane must be designed for
the conditions prescribed in paragraph
(a) of this section, except that the airplane load factor need not exceed 1.0,

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[Doc. No. 27902, 61 FR 5221, Feb. 9, 1996; 61 FR
9533, Mar. 8, 1996; Doc. No. FAA-2013-0142; 79
FR 73467, Dec. 11, 2014; Amdt. 25-141, 80 FR
4762, Jan. 29, 2015; 80 FR 6435, Feb. 5, 2015]

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-18, 33 FR 12226, Aug. 30,
1968; Amdt. 25-72, 55 FR 37607, Sept. 12, 1990;
Amdt. 25-86, 61 FR 5221, Feb. 9, 1996; Amdt.
25-141, 79 FR 73468, Dec. 11, 2014]