title-14-part-23-sec23-2255

184

14 CFR Ch. I (1–1–24 Edition)

§ 23.2230

Limit and ultimate loads.

The applicant must determine—
(a) The limit loads, which are equal

to the structural design loads unless
otherwise specified elsewhere in this
part; and

(b) The ultimate loads, which are

equal to the limit loads multiplied by a
1.5 factor of safety unless otherwise
specified elsewhere in this part.

TRUCTURAL

ERFORMANCE

§ 23.2235

Structural strength.

The structure must support:
(a) Limit loads without—
(1) Interference with the safe oper-

ation of the airplane; and

(2) Detrimental permanent deforma-

tion.

(b) Ultimate loads.

§ 23.2240

Structural durability.

(a) The applicant must develop and

implement inspections or other proce-
dures to prevent structural failures due
to foreseeable causes of strength deg-
radation, which could result in serious
or fatal injuries, or extended periods of
operation with reduced safety margins.
Each of the inspections or other proce-
dures developed under this section
must be included in the Airworthiness
Limitations Section of the Instructions
for Continued Airworthiness required
by § 23.1529.

(b) For Level 4 airplanes, the proce-

dures developed for compliance with
paragraph (a) of this section must be
capable of detecting structural damage
before the damage could result in
structural failure.

continued safe flight and landing fol-
lowing a sudden release of cabin pres-
sure, including sudden releases caused
by door and window failures.

(2) For airplanes with maximum op-

erating altitude greater than 41,000
feet, the procedures developed for com-
pliance with paragraph (a) of this sec-
tion must be capable of detecting dam-
age to the pressurized cabin structure
before the damage could result in rapid
decompression that would result in se-
rious or fatal injuries.

(d) The airplane must be designed to

minimize hazards to the airplane due

to structural damage caused by high-
energy fragments from an uncontained
engine or rotating machinery failure.

§ 23.2245

Aeroelasticity.

(a) The airplane must be free from

flutter, control reversal, and diver-
gence—

(1) At all speeds within and suffi-

ciently beyond the structural design
envelope;

(2) For any configuration and condi-

tion of operation;

(3) Accounting for critical degrees of

freedom; and

(4) Accounting for any critical fail-

ures or malfunctions.

(b) The applicant must establish tol-

erances for all quantities that affect
flutter.

ESIGN

§ 23.2250

Design and construction

principles.

(a) The applicant must design each

part, article, and assembly for the ex-
pected operating conditions of the air-
plane.

(b) Design data must adequately de-

fine the part, article, or assembly con-
figuration, its design features, and any
materials and processes used.

suitability of each design detail and
part having an important bearing on
safety in operations.

(d) The control system must be free

from jamming, excessive friction, and
excessive deflection when the airplane
is subjected to expected limit airloads.

(e) Doors, canopies, and exits must be

protected against inadvertent opening
in flight, unless shown to create no
hazard when opened in flight.

§ 23.2255

Protection of structure.

(a) The applicant must protect each

part of the airplane, including small
parts such as fasteners, against dete-
rioration or loss of strength due to any
cause likely to occur in the expected
operational environment.

(b) Each part of the airplane must

have adequate provisions for ventila-
tion and drainage.

tenance, preventive maintenance, or

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§ 23.2270

servicing, the applicant must incor-
porate a means into the airplane design
to allow such actions to be accom-
plished.

[Doc. No. FAA–2015–1621, Amdt. 23–64, 81 FR
96689, Dec. 30, 2016, as amended by Doc. No.
FAA–2022–1355, Amdt. 23–65, 87 FR 75710, Dec.
9, 2022]

§ 23.2260

Materials and processes.

(a) The applicant must determine the

suitability and durability of materials
used for parts, articles, and assemblies,
accounting for the effects of likely en-
vironmental conditions expected in
service, the failure of which could pre-
vent continued safe flight and landing.

(b) The methods and processes of fab-

rication and assembly used must
produce consistently sound structures.
If a fabrication process requires close
control to reach this objective, the ap-
plicant must perform the process under
an approved process specification.

(f) and (g) of this section, the applicant
must select design values that ensure
material strength with probabilities
that account for the criticality of the
structural element. Design values must
account for the probability of struc-
tural failure due to material varia-
bility.

(d) If material strength properties

are required, a determination of those
properties must be based on sufficient
tests of material meeting specifica-
tions to establish design values on a
statistical basis.

(e) If thermal effects are significant

on a critical component or structure
under normal operating conditions, the
applicant must determine those effects
on allowable stresses used for design.

(f) Design values, greater than the

minimums specified by this section,
may be used, where only guaranteed
minimum values are normally allowed,
if a specimen of each individual item is
tested before use to determine that the
actual strength properties of that par-
ticular item will equal or exceed those
used in the design.

(g) An applicant may use other mate-

rial design values if approved by the
Administrator.

§ 23.2265

Special factors of safety.

(a) The applicant must determine a

special factor of safety for each critical
design value for each part, article, or
assembly for which that critical design
value is uncertain, and for each part,
article, or assembly that is—

(1) Likely to deteriorate in service

before normal replacement; or

(2) Subject to appreciable variability

because of uncertainties in manufac-
turing processes or inspection methods.

(b) The applicant must determine a

special factor of safety using quality
controls and specifications that ac-
count for each—

(1) Type of application;
(2) Inspection method;
(3) Structural test requirement;
(4) Sampling percentage; and
(5) Process and material control.
(c) The applicant must multiply the

highest pertinent special factor of safe-
ty in the design for each part of the
structure by each limit and ultimate
load, or ultimate load only, if there is
no corresponding limit load, such as
occurs with emergency condition load-
ing.

TRUCTURAL

CCUPANT

ROTECTION

§ 23.2270

Emergency conditions.

(a) The airplane, even when damaged

in an emergency landing, must protect
each occupant against injury that
would preclude egress when—

(1) Properly using safety equipment

and features provided for in the design;

(2) The occupant experiences ulti-

mate static inertia loads likely to
occur in an emergency landing; and

(3) Items of mass, including engines

or auxiliary power units (APUs), with-
in or aft of the cabin, that could injure
an occupant, experience ultimate stat-
ic inertia loads likely to occur in an
emergency landing.

(b) The emergency landing conditions

specified in paragraph (a)(1) and (a)(2)
of this section, must—

(1) Include dynamic conditions that

are likely to occur in an emergency
landing; and

(2) Not generate loads experienced by

the occupants, which exceed estab-
lished human injury criteria for human
tolerance due to restraint or contact
with objects in the airplane.