FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 7. Aircraft Hardware, Control Cables, and Turnbuckles | 7. Safetying | 7-123. Safety Wire
9/8/98
SECTION 7. SAFETYING
AC 43.13-1B
7-122. GENERAL. The word safetying is a
term universally used in the aircraft industry.
Briefly, safetying is defined as: “Securing by
various means any nut, bolt, turnbuckle etc.,
on the aircraft so that vibration will not cause
it to loosen during operation.” These practices
are not a means of obtaining or maintaining
torque, rather a safety device to prevent the
disengagement of screws, nuts, bolts, snap
rings, oil caps, drain cocks, valves, and parts.
Three basic methods are used in safetying;
safety-wire, cotter pins, and self-locking nuts.
Retainer washers and pal nuts are also some-
times used.
a. Wire, either soft brass or steel is used
on cylinder studs, control cable turnbuckles,
and engine accessory attaching bolts.
b. Cotter pins are used on aircraft and
engine controls, landing gear, and tailwheel as-
semblies, or any other point where a turning or
actuating movement takes place.
c. Self-locking nuts are used in applica-
tions where they will not be removed often.
Repeated removal and installation will cause
the self-locking nut to lose its locking feature.
They should be replaced when they are no
longer capable of maintaining the minimum
prevailing torque. (See table 7-2.)
d. Pal or speed nuts include designs
which force the nut thread against the bolt or
screw thread when tightened. These nuts
should never be reused and should be replaced
with new ones when removed.
7-123. SAFETY WIRE. Do not use stain-
less steel, monel, carbon steel, or aluminum
alloy safety wire to secure emergency mecha-
nisms such as switch handles, guards covering
handles used on exits, fire extinguishers,
emergency gear releases, or other emergency
equipment. Some existing structural equip-
ment or safety-of-flight emergency devices re-
quire copper or brass safety wire (.020 inch di-
ameter only). Where successful emergency
operation of this equipment is dependent on
shearing or breaking of the safety wire, par-
ticular care should be used to ensure that safe-
tying does not prevent emergency operation.
a. There are two methods of safety
wiring; the double-twist method that is most
commonly used, and the single-wire method
used on screws, bolts, and/or nuts in a closely-
spaced or closed-geometrical pattern such as a
triangle, square, rectangle, or circle. The sin-
gle-wire method may also be used on parts in
electrical systems and in places that are diffi-
cult to reach. (See figures 7-3 and 7-3a.)
b. When using double-twist method of
safety wiring, .032 inch minimum diameter
wire should be used on parts that have a hole
diameter larger than .045 inch. Safety wire of
.020 inch diameter (double strand) may be
used on parts having a nominal hole diameter
between .045 and .062 inch with a spacing
between parts of less than 2 inches. When
using the single-wire method, the largest size
wire that the hole will accommodate should be
used. Copper wire (.020 inch diameter), alu-
minum wire (.031 inch diameter), or other
similar wire called for in specific technical or-
ders, should be used as seals on equipment
such as first-aid kits, portable fire extinguish-
ers, emergency valves, or oxygen regulators.
CAUTION: Care should be taken not
to confuse steel with aluminum wire.
c. A secure seal indicates that the com-
ponent has not been opened. Some emergency
devices require installation of brass or soft
Par 7-122
Page 7-19