399 

Federal Aviation Administration, DOT 

§ 25.331 

load tests in cases where limit load 
tests may be inadequate. 

(b)–(c) [Reserved] 
(d) When static or dynamic tests are 

used to show compliance with the re-
quirements of § 25.305(b) for flight 
structures, appropriate material cor-
rection factors must be applied to the 
test results, unless the structure, or 
part thereof, being tested has features 
such that a number of elements con-
tribute to the total strength of the 
structure and the failure of one ele-
ment 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] 

F

LIGHT

L

OADS

 

§ 25.321

General. 

(a) Flight load factors represent the 

ratio of the aerodynamic force compo-
nent (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 ef-

fects 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 max-
imum weight appropriate to each par-
ticular 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 max-
imum load for each part of the airplane 
structure is obtained. 

(d) The significant forces acting on 

the airplane must be placed in equi-
librium 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 equi-
librium with thrust and all aero-
dynamic 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] 

F

LIGHT

M

ANEUVER AND

G

UST

 

C

ONDITIONS

 

§ 25.331

Symmetric maneuvering con-

ditions. 

(a) 

Procedure.  For the analysis of the 

maneuvering flight conditions specified 
in paragraphs (b) and (c) of this sec-
tion, 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 con-
trol system. 

(2) In determining elevator angles 

and chordwise load distribution in the 
maneuvering conditions of paragraphs 
(b) and (c) of this section, the effect of 
corresponding pitching velocities must 
be taken into account. The in-trim and 
out-of-trim flight conditions specified 
in § 25.255 must be considered. 

(b) 

Maneuvering balanced conditions. 

Assuming the airplane to be in equi-
librium with zero pitching accelera-
tion, the maneuvering conditions A 
through I on the maneuvering envelope 
in § 25.333(b) must be investigated. 

(c) 

Pitch maneuver conditions. The 

conditions specified in paragraphs 
(c)(1) and (2) of this section must be in-
vestigated. The movement of the pitch 
control surfaces may be adjusted to 
take into account limitations imposed 
by the maximum pilot effort specified 
by § 25.397(b), control system stops and 
any indirect effect imposed by limita-
tions in the output side of the control 
system (for example, stalling torque or 
maximum rate obtainable by a power 
control system.) 

(1) 

Maximum pitch control displacement 

at V

A

. The airplane is assumed to be 

flying in steady level flight (point A

1

, 

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