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 | 3. Bolts | 7-43. Engine Bolts
9/8/98
AC 43.13-1B
d. Add the friction drag torque to the
desired torque. This is referred to as “final
torque,” which should register on the indicator
or setting for a snap-over type torque wrench.
e. Apply a smooth even pull when ap-
plying torque pressure. If chattering or a jerk-
ing motion occurs during final torque, back off
the nut and retorque.
NOTE: Many applications of bolts in
aircraft/engines require stretch checks
prior to reuse. This requirement is
due primarily to bolt stretching
caused by overtorquing.
f. When installing a castle nut, start
alignment with the cotter pin hole at the mini-
mum recommended torque plus friction drag
torque.
NOTE: Do not exceed the maximum
torque plus the friction drag. If the
hole and nut castellation do not align,
change washer or nut and try again.
Exceeding the maximum recom-
mended torque is not recommended.
g. When torque is applied to bolt heads
or capscrews, apply the recommended torque
plus friction drag torque.
h. If special adapters are used which
will change the effective length of the torque
wrench, the final torque indication or wrench
setting must be adjusted accordingly. Deter-
mine the torque wrench indication or setting
with adapter installed as shown in figure 7-2.
i. Table 7-1 shows the recommended
torque to be used when specific torque is not
supplied by the manufacturer. The table in-
cludes standard nut and bolt combinations,
currently used in aviation maintenance. For
further identification of hardware, see chap-
ter 7, section 11.
7-41. STANDARD AIRCRAFT HEX
HEAD BOLTS (AN3 THROUGH AN20).
These are all-purpose structural bolts used for
general applications that require tension or
shear loads. Steel bolts smaller than
No. 10-32, and aluminum alloy bolts smaller
than 1/4 inch diameter, should not be used in
primary structures. Do not use aluminum bolts
or nuts in applications requiring frequent re-
moval for inspection or maintenance.
7-42. DRILLED HEAD BOLTS (AN73
THROUGH AN81). The AN drilled head
bolt is similar to the standard hex bolt, but has
a deeper head which is drilled to receive safety
wire. The physical differences preventing di-
rect interchangeability are the slightly greater
head height, and longer thread length of the
AN73 through AN81 series. The AN73
through AN81 drilled head bolts have been su-
perseded by MS20073, for fine thread bolts
and MS20074 for coarse thread bolts. AN73,
AN74, MS20073, and MS20074 bolts of like
thread and grip lengths are universally, func-
tionally, and dimensionally interchangeable.
7-43. ENGINE BOLTS. These are hex
head bolts (AN101001 through AN101900),
drilled shank hex head bolts (AN101901
through AN102800), drilled hex head (one
hole) bolts (AN102801 through AN103700),
and drilled hex head (six holes) bolts
(AN103701 through AN104600). They are
similar to each other except for the holes in the
head and shank. Hex head bolts (AN104601
through AN105500), drilled shank hex head
bolts (AN105501 through AN106400), drilled
hex head (one hole) bolts (AN106401 through
AN107300), and drilled hex head (six holes)
bolts (AN107301 through AN108200) are
similar to the bolts described in para-
graph 7-42, except that this series is manufac-
tured from corrosion-resistant steel.
Par 7-40
Page 7-7