264
14 CFR Ch. I (1–1–24 Edition)
§ 25.619
structural failures due to material var-
iability. Except as provided in para-
graphs (e) and (f) of this section, com-
pliance must be shown by selecting ma-
terial design values which assure mate-
rial strength with the following prob-
ability:
(1) Where applied loads are eventu-
ally distributed through a single mem-
ber within an assembly, the failure of
which would result in loss of structural
integrity of the component, 99 percent
probability with 95 percent confidence.
(2) For redundant structure, in which
the failure of individual elements
would result in applied loads being
safely distributed to other load car-
rying members, 90 percent probability
with 95 percent confidence.
(c) The effects of environmental con-
ditions, such as temperature and mois-
ture, on material design values used in
an essential component or structure
must be considered where these effects
are significant within the airplane op-
erating envelope.
(d) [Reserved]
(e) Greater material design values
may be used if a ‘‘premium selection’’
of the material is made in which 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 design.
(f) Other material design values may
be used if approved by the Adminis-
trator.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–46, 43 FR 50595, Oct. 30,
1978; Amdt. 25–72, 55 FR 29776, July 20, 1990;
Amdt. 25–112, 68 FR 46431, Aug. 5, 2003]
§ 25.619
Special factors.
The factor of safety prescribed in
§ 25.303 must be multiplied by the high-
est pertinent special factor of safety
prescribed in §§ 25.621 through 25.625 for
each part of the structure whose
strength is—
(a) Uncertain;
(b) Likely to deteriorate in service
before normal replacement; or
(c) Subject to appreciable variability
because of uncertainties in manufac-
turing processes or inspection methods.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5674, Apr. 8,
1970]
§ 25.621
Casting factors.
(a)
General. For castings used in
structural applications, the factors,
tests, and inspections specified in para-
graphs (b) through (d) of this section
must be applied in addition to those
necessary to establish foundry quality
control. The inspections must meet ap-
proved specifications. Paragraphs (c)
and (d) of this section apply to any
structural castings, except castings
that are pressure tested as parts of hy-
draulic or other fluid systems and do
not support structural loads.
(b)
Bearing stresses and surfaces. The
casting factors specified in paragraphs
(c) and (d) of this section—
(1) Need not exceed 1.25 with respect
to bearing stresses regardless of the
method of inspection used; and
(2) Need not be used with respect to
the bearing surfaces of a part whose
bearing factor is larger than the appli-
cable casting factor.
(c)
Critical castings. Each casting
whose failure could preclude continued
safe flight and landing of the airplane
or could result in serious injury to oc-
cupants is a critical casting. Each crit-
ical casting must have a factor associ-
ated with it for showing compliance
with strength and deformation require-
ments of § 25.305, and must comply with
the following criteria associated with
that factor:
(1) A casting factor of 1.0 or greater
may be used, provided that—
(i) It is demonstrated, in the form of
process qualification, proof of product,
and process monitoring that, for each
casting design and part number, the
castings produced by each foundry and
process combination have coefficients
of variation of the material properties
that are equivalent to those of wrought
alloy products of similar composition.
Process monitoring must include test-
ing of coupons cut from the prolonga-
tions of each casting (or each set of
castings, if produced from a single pour
into a single mold in a runner system)
and, on a sampling basis, coupons cut
from critical areas of production cast-
ings. The acceptance criteria for the
process monitoring inspections and
tests must be established and included
in the process specifications to ensure
VerDate Sep<11>2014
09:06 Jun 28, 2024
Jkt 262046
PO 00000
Frm 00274
Fmt 8010
Sfmt 8010
Y:\SGML\262046.XXX
262046
jspears on DSK121TN23PROD with CFR
265
Federal Aviation Administration, DOT
§ 25.621
the properties of the production cast-
ings are controlled to within levels
used in design.
(ii) Each casting receives:
(A) Inspection of 100 percent of its
surface, using visual inspection and liq-
uid penetrant or equivalent inspection
methods; and
(B) Inspection of structurally signifi-
cant internal areas and areas where de-
fects are likely to occur, using radio-
graphic or equivalent inspection meth-
ods.
(iii) One casting undergoes a static
test and is shown to meet the strength
and deformation requirements of
§ 25.305(a) and (b).
(2) A casting factor of 1.25 or greater
may be used, provided that—
(i) Each casting receives:
(A) Inspection of 100 percent of its
surface, using visual inspection and liq-
uid penetrant or equivalent inspection
methods; and
(B) Inspection of structurally signifi-
cant internal areas and areas where de-
fects are likely to occur, using radio-
graphic or equivalent inspection meth-
ods.
(ii) Three castings undergo static
tests and are shown to meet:
(A) The strength requirements of
§ 25.305(b) at an ultimate load cor-
responding to a casting factor of 1.25;
and
(B) The deformation requirements of
§ 25.305(a) at a load of 1.15 times the
limit load.
(3) A casting factor of 1.50 or greater
may be used, provided that—
(i) Each casting receives:
(A) Inspection of 100 percent of its
surface, using visual inspection and liq-
uid penetrant or equivalent inspection
methods; and
(B) Inspection of structurally signifi-
cant internal areas and areas where de-
fects are likely to occur, using radio-
graphic or equivalent inspection meth-
ods.
(ii) One casting undergoes a static
test and is shown to meet:
(A) The strength requirements of
§ 25.305(b) at an ultimate load cor-
responding to a casting factor of 1.50;
and
(B) The deformation requirements of
§ 25.305(a) at a load of 1.15 times the
limit load.
(d)
Non-critical castings. For each
casting other than critical castings, as
specified in paragraph (c) of this sec-
tion, the following apply:
(1) A casting factor of 1.0 or greater
may be used, provided that the require-
ments of (c)(1) of this section are met,
or all of the following conditions are
met:
(i) Castings are manufactured to ap-
proved specifications that specify the
minimum mechanical properties of the
material in the casting and provides
for demonstration of these properties
by testing of coupons cut from the
castings on a sampling basis.
(ii) Each casting receives:
(A) Inspection of 100 percent of its
surface, using visual inspection and liq-
uid penetrant or equivalent inspection
methods; and
(B) Inspection of structurally signifi-
cant internal areas and areas where de-
fects are likely to occur, using radio-
graphic or equivalent inspection meth-
ods.
(iii) Three sample castings undergo
static tests and are shown to meet the
strength and deformation requirements
of § 25.305(a) and (b).
(2) A casting factor of 1.25 or greater
may be used, provided that each cast-
ing receives:
(i) Inspection of 100 percent of its sur-
face, using visual inspection and liquid
penetrant or equivalent inspection
methods; and
(ii) Inspection of structurally signifi-
cant internal areas and areas where de-
fects are likely to occur, using radio-
graphic or equivalent inspection meth-
ods.
(3) A casting factor of 1.5 or greater
may be used, provided that each cast-
ing receives inspection of 100 percent of
its surface using visual inspection and
liquid penetrant or equivalent inspec-
tion methods.
(4) A casting factor of 2.0 or greater
may be used, provided that each cast-
ing receives inspection of 100 percent of
its surface using visual inspection
methods.
(5) The number of castings per pro-
duction batch to be inspected by non-
visual methods in accordance with
paragraphs (d)(2) and (3) of this section
VerDate Sep<11>2014
09:06 Jun 28, 2024
Jkt 262046
PO 00000
Frm 00275
Fmt 8010
Sfmt 8010
Y:\SGML\262046.XXX
262046
jspears on DSK121TN23PROD with CFR
266
14 CFR Ch. I (1–1–24 Edition)
§ 25.623
may be reduced when an approved qual-
ity control procedure is established.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–139, 79 FR 59429, Oct. 2,
2014]
§ 25.623
Bearing factors.
(a) Except as provided in paragraph
(b) of this section, each part that has
clearance (free fit), and that is subject
to pounding or vibration, must have a
bearing factor large enough to provide
for the effects of normal relative mo-
tion.
(b) No bearing factor need be used for
a part for which any larger special fac-
tor is prescribed.
§ 25.625
Fitting factors.
For each fitting (a part or terminal
used to join one structural member to
another), the following apply:
(a) For each fitting whose strength is
not proven by limit and ultimate load
tests in which actual stress conditions
are simulated in the fitting and sur-
rounding structures, a fitting factor of
at least 1.15 must be applied to each
part of—
(1) The fitting;
(2) The means of attachment; and
(3) The bearing on the joined mem-
bers.
(b) No fitting factor need be used—
(1) For joints made under approved
practices and based on comprehensive
test data (such as continuous joints in
metal plating, welded joints, and scarf
joints in wood); or
(2) With respect to any bearing sur-
face for which a larger special factor is
used.
(c) For each integral fitting, the part
must be treated as a fitting up to the
point at which the section properties
become typical of the member.
(d) For each seat, berth, safety belt,
and harness, the fitting factor specified
in § 25.785(f)(3) applies.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5674, Apr. 8,
1970; Amdt. 25–72, 55 FR 29776, July 20, 1990]
§ 25.629
Aeroelastic stability require-
ments.
(a)
General. The aeroelastic stability
evaluations required under this section
include flutter, divergence, control re-
versal and any undue loss of stability
and control as a result of structural de-
formation. The aeroelastic evaluation
must include whirl modes associated
with any propeller or rotating device
that contributes significant dynamic
forces. Compliance with this section
must be shown by analyses, wind tun-
nel tests, ground vibration tests, flight
tests, or other means found necessary
by the Administrator.
(b)
Aeroelastic stability envelopes. The
airplane must be designed to be free
from aeroelastic instability for all con-
figurations and design conditions with-
in the aeroelastic stability envelopes
as follows:
(1) For normal conditions without
failures, malfunctions, or adverse con-
ditions, all combinations of altitudes
and speeds encompassed by the V
D
/M
D
versus altitude envelope enlarged at all
points by an increase of 15 percent in
equivalent airspeed at both constant
Mach number and constant altitude. In
addition, a proper margin of stability
must exist at all speeds up to V
D
/M
D
and, there must be no large and rapid
reduction in stability as V
D
/M
D
is ap-
proached. The enlarged envelope may
be limited to Mach 1.0 when M
D
is less
than 1.0 at all design altitudes, and
(2) For the conditions described in
§ 25.629(d) below, for all approved alti-
tudes, any airspeed up to the greater
airspeed defined by;
(i) The V
D
/M
D
envelope determined by
§ 25.335(b); or,
(ii) An altitude-airspeed envelope de-
fined by a 15 percent increase in equiv-
alent airspeed above V
C
at constant al-
titude, from sea level to the altitude of
the intersection of 1.15 V
C
with the ex-
tension of the constant cruise Mach
number line, M
C
, then a linear vari-
ation in equivalent airspeed to M
C
+ .05
at the altitude of the lowest V
C
/M
C
intersection; then, at higher altitudes,
up to the maximum flight altitude, the
boundary defined by a .05 Mach in-
crease in M
C
at constant altitude.
(c)
Balance weights. If concentrated
balance weights are used, their effec-
tiveness and strength, including sup-
porting structure, must be substan-
tiated.
(d)
Failures, malfunctions, and adverse
conditions. The failures, malfunctions,
and adverse conditions which must be
VerDate Sep<11>2014
09:06 Jun 28, 2024
Jkt 262046
PO 00000
Frm 00276
Fmt 8010
Sfmt 8010
Y:\SGML\262046.XXX
262046
jspears on DSK121TN23PROD with CFR