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Safetying Aircraft hardware

Aircraft Turnbuckles

In part five we discuss turnbuckle assemblies, how to safety them and we describe two methods to do that. Bolts are to be safetied as well, it is not that difficult and with a little practice you can make some nice examples.

Turnbuckle assemblies are used with control cables to provide desired cable tension. They are made in a range of sizes and in both long "L" and short "S" assemblies.

The long assembly is indicated by the letter "L" following the dash number, and the short assembly is indicated by the letter "S". The size is given by the dash number indicating the rated strength of the assembly in hundreds of pounds.

The assemblies are made up of three parts (1 barrel and 2 ends). The barrel is made of brass and the ends of 2330 nickel steel heat treated by 125,000 lbs. per sq. inch and Cadmium plated. The threads on all parts are class 3NF.

Turnbuckle Assemblies & Safety wiring

Safety all turnbuckles with safety wire using either the double or single wrap method, or any appropriately approved special safetying device complying with the requirements of FAA Technical Standard Order TSO-C21. The swaged and unswaged turnbuckle assemblies are covered by AN Standard Drawings. Do not ever reuse safety wire. Adjust the turnbuckle to the correct cable tension so that no more than three threads are exposed on either side of the turnbuckle barrel. Do not lubricate turnbuckles.

Aircraft turnbuckle

Double Wrap method

Of the methods using safety wire for safetying turnbuckles, the method described here is preferred, although either of the other methods described is satisfactory. The method of double wrap safetying is shown below use two separate lengths of the proper wire. Run one end of the wire through the hole in the barrel of the turnbuckle and bend the end of the wire towards opposite ends of the turnbuckle. Then pass the second length of the wire into the hole in the barrel and bend the ends along the barrel on the side opposite the first.

Spiral the two wires in opposite directions around the barrel to cross each other twice between the center hole and the ends. Then pass the wires at the end of the turnbuckle in opposite directions through the holes in the turnbuckle eyes or between the jaws of the turnbuckle fork, as applicable, laying one wire along the barrel and wrapping the other at least four times around the shank of the turnbuckle and binding the laid wires in place before cutting the wrapped wire off. Wrap the remaining length of safety wire at least four turns around the shank and cut it off. Repeat the procedure at the opposite end of the turnbuckle.

When a swaged terminal is being safetied, pass the ends of both wires, if possible, through the hole provided in the terminal for this purpose and wrap both ends around the shank as described above. When the hole in the terminal is not large enough to accommodate the ends of both wires, the hole may be enlarged slightly. If the hole is not large enough to allow passage of both wires, pass the wire through the hole and loop it over the free end of the other wire, and then wrap both ends around the shank as described.

Aircraft turnbuckle

Above you can clearly see the difference between the single and double wrap method.

Safetying methods

Safety Wire ToolAircraft Safety Wire Tool
Safety wiring tool

All aircraft hardware needs to be safetied one way or the other. Nearly all hardware found on an aircraft has provisions to safety it. Safety wiring means preventing the bolt, nut or whatever from coming loose and departing the aircraft sooner than we think or want. After all: an aircraft is a bunch of parts flying in very close formation, lets keep it that way. There are several techniques to safety hardware and as a picture says more than a thousands words or pages on this website:

Safetying Aircraft hardware

Just think of the direction you must turn a bolt to loosen it, then safety it to the other direction. The correct way to safety wire an bolt is shown in the image below:

Safetying Aircraft hardware the right way

Written by EAI.



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