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of TmnsporTation
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Avidon
Admlnistmtiofl
Circular -
subj@: USE OF SOCIETY OF AUTOMOTIVE
Date: VW87
AC NO: 20-127
ENGINEERS (SAE) CLASS HI1 BOLTS
Initiated by: ANM- 110
ChgC
1 ,PURPOSE.
This Advisory Circular (AC) provides guidance on the use of
S&i-Automotive Engineers (SAE) Class Hll bolts in primary structure on
all aircraft, including gliders and manned free balloons, and on aircraft
engines and propellers.
2
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RELATED FAR SECTIONS. This guidance is
provided for showing compliance with
requirements of Sections 21.21, 23.603,
25.603, 27.603, 29.603, 33.15, and
35.17 of the Federal Aviation Regulations (FAR).
3 BACKGROUND.
The service history of Hll bolts used in primary structure
l
i;dicates a higher than normal failure rate.
These failures are attributed to
stress corrosion cracking and may become a safety problem.
Hll bolts and
companion nuts are more sensitive to environmental influence than bolts made
from other materials.
The use of Hll bolts in primary structure' is therefore
discouraged and should not be considered for use on new type design aircraft.
There are other fasteners available which have demonstrated satisfactory service
experience.
Inconel 718 and stainless steel bolts are examples of acceptable
substitutes.
4 . GENERAL CONSIDERATIONS.
a.
Hll bolts and nuts should be replaced with a different type of bolt and
.
nut of equivalent strength and f
.
.
atlgue rating, if any of the following
conditions exist:
(1) The bolt s are exposed to high temperature (above 2500 F) and
possible simultaneous exposure to hydraulic fluids.
(2) The bolts are exposed to a corrosive environment such as moisture,
salt air, exhaust gases, etc., at ambient temperature.
(3) The bolts are used primarily in tension application with a high
sustained tensile stress, in any environment continually exposed to weather.
(4) The bolts are used in any application, including both tension or
shear, in which a single failure could be catastrophic.
(5) The bolts are used in any application which requires frequent
*
inspections of the bolts.
t
(6) The bolt
service history indicates a need for frequent replacement.
.
c-
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