Advisory
Circular
US Department
of Transportaton
Federal Aviation
Administration
Subject:
SELF-LOCKING NUTS OX
Date:
August 24,
1984 AC %I: 23.607-l
BOLTS SURJECT TO KOT.L\TION
Initiated by: ACE- 100
Change:
1.
PURPOSE.
This advisory circular provides informat ion and guidance concerning
acceptable means, but not the only means, of compliance with Part 3 of the Civil
Air Regulations
(CAK)
and with Part 23 of the Federal Aviation Regulations (FAR)
applicable to self-locking nuts used on bolts subject to rotation in operation.
2.
REIATED
FAR AND CAR SECTION.
Section 23.607 and Section 3.294.
3. BACKGROUND. CAR Section 3.294 and FAR Section 23.607 require that no self-
locking nut may be used on any bolt subject to rotation in operation unless a non-
friction locking device is used in addition to the self-locking device.
No speci-
fic systems in the airplane are named where the double-lock feature is required.
In the past,
this section was not uniformly applied.
For some projects, bolts
which were installed through a bushing. bearing or uniball were required to have
only a self-locking nut for retention since there was no relati.ve motion between
the bolt and the surface against which it was bearing. On other projects for a
similar installation. a nonfriction locking device, in addition to the self-locking
nut, was required because it was deemed possible for the bushing, bearing or
uniball to seize, thus transmitting the relative motion to the bolt.
4.
APPLICATION. This guidance material is applicable for new, amended and
supplemental type certificates and alterations using self-locking nuts on bolts
subject to rotation.
5.
ACCEPTABLE MEANS OF COMPLIANCE. For the systems and areas noted below, one
means for showing compliance with the requirements of CAR Section 3.29& and FAR
Sectton 23.607 is as follows:
a. Self-locking nuts alone should not be used in any system when movement of
the joint may result in motion of the nut or bolt head relative to the surface
against which it is bearing.
Joint seizure (bearing, uniball, or bushing seizure)
does not have to be considered by this regulation when determining the relative
motion of the parts in question, although it is advisable to do so.
Suitable
protection and material properties of the joint are required by Sections 23.609 and
23.613.
b.
Self-locking castrllated nuts with cotter pins or lockwire may be used in
any system.
C.
Self-locking nuts should not be used with bolts or screws on turbine
engine airplanes in locations where
the
loose nut, bolt, washer or screw could fall
or be drawn into the engine air intake scoop.
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