title-14-part-27-sec27-653

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14 CFR Ch. I (1–1–24 Edition)

§ 27.623

(i) The strength requirements of

§ 27.305 at an ultimate load cor-
responding to a casting factor of 1.25;
and

(ii) The deformation requirements of

§ 27.305 at a load of 1.15 times the limit
load.

(d)

Noncritical castings. For each cast-

ing other than those specified in para-
graph (c) of this section, the following
apply:

(1) Except as provided in paragraphs

(d)(2) and (3) of this section, the casting
factors and corresponding inspections
must meet the following table:

Casting factor

Inspection

2.0 or greater ...............

100 percent visual.

Less than 2.0, greater

than 1.5.

100 percent visual, and magnetic

particle (ferromagnetic materials),
penetrant (nonferromagnetic ma-
terials), or approved equivalent
inspection methods.

1.25 through 1.50 ........

100 percent visual, and magnetic

particle (ferromagnetic materials).
penetrant (nonferromagnetic ma-
terials), and radiographic or ap-
proved equivalent inspection
methods.

(2) The percentage of castings in-

spected by nonvisual methods may be
reduced below that specified in para-
graph (d)(1) of this section when an ap-
proved quality control procedure is es-
tablished.

(3) For castings procured to a speci-

fication that guarantees the mechan-
ical properties of the material in the
casting and provides for demonstration
of these properties by test of coupons
cut from the castings on a sampling
basis—

(i) A casting factor of 1.0 may be

used; and

(ii) The castings must be inspected as

provided in paragraph (d)(1) of this sec-
tion for casting factors of ‘‘1.25 through
1.50’’ and tested under paragraph (c)(2)
of this section.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–34, 62 FR 46173, Aug. 29,
1997]

§ 27.623

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 on

a part for which any larger special fac-
tor is prescribed.

§ 27.625

Fitting factors.

For each fitting (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); and

(2) With respect to any bearing sur-

face for which a larger special factor is
used.

must be treated as a fitting up to the
point at which the section properties
become typical of the member.

(d) Each seat, berth, litter, safety

belt, and harness attachment to the
structure must be shown by analysis,
tests, or both, to be able to withstand
the inertia forces prescribed in
§ 27.561(b)(3) multiplied by a fitting fac-
tor of 1.33.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–35, 63 FR 43285, Aug. 12,
1998]

§ 27.629

Flutter.

Each aerodynamic surface of the

rotorcraft must be free from flutter
under each appropriate speed and
power condition.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–26, 55 FR 8000, Mar. 6,
1990]

OTORS

§ 27.653

Pressure venting and drain-

age of rotor blades.

(a) For each rotor blade—

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§ 27.672

(1) There must be means for venting

the internal pressure of the blade;

(2) Drainage holes must be provided

for the blade; and

(3) The blade must be designed to pre-

vent water from becoming trapped in
it.

(b) Paragraphs (a)(1) and (2) of this

section does not apply to sealed rotor
blades capable of withstanding the
maximum pressure differentials ex-
pected in service.

[Amdt. 27–2, 33 FR 963, Jan. 26, 1968]

§ 27.659

Mass balance.

(a) The rotors and blades must be

mass balanced as necessary to—

(1) Prevent excessive vibration; and
(2) Prevent flutter at any speed up to

the maximum forward speed.

(b) The structural integrity of the

mass balance installation must be sub-
stantiated.

[Amdt. 27–2, 33 FR 963, Jan. 26, 1968]

§ 27.661

Rotor blade clearance.

There must be enough clearance be-

tween the rotor blades and other parts
of the structure to prevent the blades
from striking any part of the structure
during any operating condition.

[Amdt. 27–2, 33 FR 963, Jan. 26, 1968]

§ 27.663

Ground resonance prevention

means.

(a) The reliability of the means for

preventing ground resonance must be
shown either by analysis and tests, or
reliable service experience, or by show-
ing through analysis or tests that mal-
function or failure of a single means
will not cause ground resonance.

(b) The probable range of variations,

during service, of the damping action
of the ground resonance prevention
means must be established and must be
investigated during the test required
by § 27.241.

[Amdt. 27–2, 33 FR 963, Jan. 26, 1968, as
amended by Amdt. 27–26, 55 FR 8000, Mar. 6,
1990]

ONTROL

YSTEMS

§ 27.671

General.

(a) Each control and control system

must operate with the ease, smooth-

ness, and positiveness appropriate to
its function.

(b) Each element of each flight con-

trol system must be designed, or dis-
tinctively and permanently marked, to
minimize the probability of any incor-
rect assembly that could result in the
malfunction of the system.

§ 27.672

Stability augmentation, auto-

matic, and power-operated systems.

If the functioning of stability aug-

mentation or other automatic or
power-operated systems is necessary to
show compliance with the flight char-
acteristics requirements of this part,
such systems must comply with § 27.671
of this part and the following:

(a) A warning which is clearly distin-

guishable to the pilot under expected
flight conditions without requiring the
pilot’s attention must be provided for
any failure in the stability augmenta-
tion system or in any other automatic
or power-operated system which could
result in an unsafe condition if the
pilot is unaware of the failure. Warning
systems must not activate the control
systems.

(b) The design of the stability aug-

mentation system or of any other auto-
matic or power-operated system must
allow initial counteraction of failures
without requiring exceptional pilot
skill or strength by overriding the fail-
ure by movement of the flight controls
in the normal sense and deactivating
the failed system.

single failure of the stability aug-
mentation system or any other auto-
matic or power-operated system—

(1) The rotorcraft is safely control-

lable when the failure or malfunction
occurs at any speed or altitude within
the approved operating limitations;

(2) The controllability and maneuver-

ability requirements of this part are
met within a practical operational
flight envelope (for example, speed, al-
titude, normal acceleration, and rotor-
craft configurations) which is described
in the Rotorcraft Flight Manual; and

(3) The trim and stability character-

istics are not impaired below a level
needed to permit continued safe flight
and landing.

[Amdt. 27–21, 49 FR 44433, Nov. 6, 1984; 49 FR
47594, Dec. 6, 1984]

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