Zlin Aviation
Section 1
Maintenance Manual Aircraft Maintenance Manual
Issued: 01/02/2006
QAP-AMM-Rev02
Date of latest Revision: 23/01/2013
Page Number: 1-14
1.1.9 RECOMMENDED FASTENER TORQUE VALUES
For more in depth information please refer also to FAA Advisory Circular AC43..13
Chapter 7.
For additional information about turnbuckle installation and inspection, or control
cables and nicopress installation and inspection, refer to chapter 1.3.6 Control cables
and pulleys.
IDENTIFICATION.
Aircraft bolts may be
identified by code markings on the bolt heads.
These markings generally denote the material of
which the bolt is made, whether the bolt is a
standard AN-type or a special-purpose bolt, and
sometimes include the manufacturer.
AN
standard steel bolts are marked with either a
raised dash or asterisk, corrosion resistant steel is
marked by a single dash, and AN aluminum-alloy
bolts are marked with two raised dashes.
LOCKING OR SAFETYING OF BOLTS
.
Lock or safety all bolts and/or nuts, except self-
locking nuts. Do not reuse cotter pins or safety
wire.
DEFINITIONS
Torque:
The importance of correct torque application cannot be overemphasized.
Undertorque can result in unnecessary wear of nuts and bolts, as well as the parts they
secure. Overtorque can cause failure of a bolt or nut from overstressing the threaded areas.
Uneven or additional loads that are applied to the assembly may result in wear or premature
failure. The following are a few simple, but important procedures, that should be followed
to ensure that correct torque is applied.
NOTE: Be sure that the torque applied is for the size of the bolt shank not the wrench size.
Running Torque: The average torque developed after the fastener is at least one full thread
through the nut, but prior to the tightening of the joint (also called self-locking torque, locking
torque, friction drag torque).
Assembly Torque: The torque required by design engineering in order to create the desired
axial load on the bolt/nut assembly (also called tightening torque or installation torque).
When nuts are to be secured to fasteners by means of cotter pins or lock wire, the low side of
the specified torque range shall be approached for tightening. If necessary, tightening shall be
continued until the next slot aligns with the hole. Nuts shall not be loosened to obtain the required
alignment. The maximum torque shall not be exceeded.
Threaded fasteners which have been torqued above the maximum value specified shall not be
backed off and re-torqued but shall be removed, rejected and rendered unserviceable.
