AC NO:
20. 71
DATE
t wvm
ADVISORY
CIRCULAR
DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
SUBJKT:
DUAL LOCKING DEVICES ON FASTENERS
1.
PURPOSE. This advisory circular provides guidance and acceptable means,
not the sole means, by which compliance may be shown with the require-
ments for dual locking devices on removable fasteners installed in
rotorcraft: and transport category airplanes.
2.
REFERENCES. Federal Aviation Regulations
25.607, 27.607,
and 29.607.
3.
BACKGROUND. It is common practice to secure fasteners (i.e., bolts,
screws, nuts, pins,
etc.) with
a
single locking device.
Service experience
has indicated that due to maintenance, manufacturing, or design errors,
a single locking device is not adequate for critical applications in
rotorcraft and transport category airplanes. Due to a number of instances
of loss of fastener integrity involving such fasteners installed on
these aircraft, it was considered necessary to require two separate
locking devices on all removable fasteners in any installation in which
the
loss of the fastener could jeopardize the safe operation of rotor-
craft
or
transport category airplanes, and that consideration must be
given to the environmental conditions associated with a particular
fastener installation in determining the appropriate locking devices
for that fastener; therefore, FARs
25.607, 27.607,
and 29,607 were
amended to specify two separate locking devices on removable fasteners
for critical applications.
4.
REMOVABLE FASTENERS. By a removable fastener in the referenced rule.8
is meant the conventional attachment devices such as bolts and nuts,
screws, pins, etc., which can be readily removed and reinstalled or
replaced by other identical fasteners.
5. LOCKING DEVICE. By a locking device is meant the feature incorporated
on the fastener which will prevent the loss of this fastener and retain
the fastener in its proper installation.
The locking devices on the
fasteners may be either friction or nonfriction types. Permanent, solid,
Initiated by:
FS-120
Downloaded from http://www.everyspec.com
