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Federal Aviation Administration, DOT 

§ 27.659 

Casting factor 


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 

(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-

(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 

(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, 

§ 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-

(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-


(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 

(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) 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, 

§ 27.629


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, 




§ 27.653

Pressure venting and drain-

age of rotor blades. 

(a) For each rotor blade— 
(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 

(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— 

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