Federal Aviation Administration, DOT

Section 25.305

need not be exceeded. In addition, the
entry speeds for flight test demonstrations at normal acceleration values
less than 1 g must be limited to the extent necessary to accomplish a recovery without exceeding VDF/MDF.
(f) In the out-of-trim condition specified in paragraph (a) of this section, it
must be possible from an overspeed
condition at VDF/MDF to produce at
least 1.5 g for recovery by applying not
more than 125 pounds of longitudinal
control force using either the primary
longitudinal control alone or the primary longitudinal control and the longitudinal trim system. If the longitudinal trim is used to assist in producing the required load factor, it must
be shown at VDF/MDF that the longitudinal trim can be actuated in the airplane nose-up direction with the primary surface loaded to correspond to
the least of the following airplane
nose-up control forces:
(1) The maximum control forces expected in service as specified in SectionSection 25.301
and 25.397.
(2) The control force required to
produce 1.5 g.
(3) The control force corresponding to
buffeting or other phenomena of such
intensity that it is a strong deterrent
to further application of primary longitudinal control force.
[Amdt. 25-42, 43 FR 2322, Jan. 16, 1978]

Subpart C - Structure

spaschal on DSK3GDR082PROD with CFR

GENERAL
Section 25.301 Loads.
(a) Strength requirements are specified in terms of limit loads (the maximum loads to be expected in service)
and ultimate loads (limit loads multiplied by prescribed factors of safety).
Unless otherwise provided, prescribed
loads are limit loads.
(b) Unless otherwise provided, the
specified air, ground, and water loads
must be placed in equilibrium with inertia forces, considering each item of
mass in the airplane. These loads must
be distributed to conservatively approximate or closely represent actual
conditions. Methods used to determine
load intensities and distribution must
be validated by flight load measurement unless the methods used for de-

termining those loading conditions are
shown to be reliable.
(c) If deflections under load would
significantly change the distribution of
external or internal loads, this redistribution must be taken into account.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5672, Apr. 8,
1970]

Section 25.303

Factor of safety.

Unless otherwise specified, a factor of
safety of 1.5 must be applied to the prescribed limit load which are considered
external loads on the structure. When a
loading condition is prescribed in
terms of ultimate loads, a factor of
safety need not be applied unless otherwise specified.
[Amdt. 25-23, 35 FR 5672, Apr. 8, 1970]

Section 25.305

Strength and deformation.

(a) The structure must be able to
support limit loads without detrimental permanent deformation. At any
load up to limit loads, the deformation
may not interfere with safe operation.
(b) The structure must be able to
support ultimate loads without failure
for at least 3 seconds. However, when
proof of strength is shown by dynamic
tests simulating actual load conditions, the 3-second limit does not
apply. Static tests conducted to ultimate load must include the ultimate
deflections and ultimate deformation
induced by the loading. When analytical methods are used to show compliance with the ultimate load strength
requirements, it must be shown that - 
(1) The effects of deformation are not
significant;
(2) The deformations involved are
fully accounted for in the analysis; or
(3) The methods and assumptions
used are sufficient to cover the effects
of these deformations.
(c) Where structural flexibility is
such that any rate of load application
likely to occur in the operating conditions might produce transient stresses
appreciably higher than those corresponding to static loads, the effects
of this rate of application must be considered.
(d) [Reserved]
(e) The airplane must be designed to
withstand any vibration and buffeting

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