Aviation Maintenance Knowledge (Safety Wire)

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Where to Find Safety Wire Standards-

Installation of safety wire can be found in the Original Equipment Manufactures’ (OEM) Maintenance Manual. In many cases it will be located in Chapter 20 Standard Practices Airframe in the AMM and Chapter 70 Standard Practices in the engine manufacture’s maintenance manual. If in the event there is not relevant information available in the OEM technical manuals, there is information available in AC 43.13-1B, Acceptable Methods Techniques, and Practices- Aircraft Inspection and Repair.

Safety Wiring Tips-

When there are two or more units, it is desirable that the holes in the units be in the same relationship to each other. Never over torque or loosen units to obtain proper alignment of the holes. It should be possible to align the wiring holes when the units are torqued within specified limits. However, if it is impossible to obtain a proper alignment of the holes without either over or under torqueing, select another unit which will permit proper alignment within the specified torque limits.

Safety Wiring Tips-

Lockwire must not be nicked, kinked, or mutilated. Never twist the wire ends off with pliers and, when cutting off ends, leave at least three complete turns after the loop, exercising extreme care to prevent the wire ends from falling into any opening. The strength of the lockwire holes is marginal, never twist the wire off with pliers. Cut the lockwire close to the hole, exercising extreme care.

Materials-

Safety Wire Types
• Monel, Inconel, or corrosion resistant wire shall be used in elevated temperature areas.
• Annealed copper wire, 0.020 inch diameter, shall be used on emergency equipment.
• Clad 5056 aluminum alloy wire shall be used for safety wire contacting magnesium to prevent galvanic corrosion.

Equipment and Methods-

Safety wire is installed because aircraft vibrate. There are many fasteners like drilled-head bolts which are often used in vibration-prone areas, they are usually safety wired together. When installing safety wire using the two methods, the wire should pull the bolt head in the direction of tightening and should be twisted evenly to the next bolt. After the end of the wire is passed through the head of the second bolt it is again twisted, this time for about three or four turns. Once this is done, the excess is cut off and the ends of the wire are bent back where they cannot cut anyone who passes their hand over the bolt.

Equipment and Materials-

Safety Wire Tips
To prevent nuts from becoming loose on studs, use castellated nuts and safety wire them as you would bolt heads.

Safety Wiring Tips-

In areas where a number of bolts must be safetied, such as a propeller, you may safety wire the bolts in groups of three. If more than three bolts are safetied together it is difficult to get the safety wire tight enough to be effective.
What’s wrong with this safety wire job?

Safety Wire Tips-

Many bolt heads must be safety wired to keep them from vibrating loose. As a general rule, no more than three bolts should be safety wired together.
Cut Pieces of Safety Wire-
Any cut pieces of safety wire must be found and disposed of properly, they are F.O.D. and can cause serious damage to aircraft and engines if not disposed of properly.

Install Safety Wire-

Installing Safety Wire on Bolts and Screws
• Safety wiring for right hand threads shall be installed as shown in the above illustrations. Safety wiring for left hand threads shall be opposite.
• The loop or double wire shall pass around, not over, the head of the bolt or screw.
• When safetying nuts and bolts, tighten to the low side of the selected torque range, and if necessary, continue tightening until a slot aligns with the safety hole.
• All fittings which require safety wiring shall be wired to the mating part or an adjacent member.

Turnbuckle Tips-

Safety Wire Requirements
When inspecting a control cable turnbuckle for proper installation, the safety wire ends should be wrapped a minimum of four turns around the terminal end shanks. When a turnbuckle is properly installed there should be no more than three threads exposed from either side of the turnbuckle barrel, and it should safetied.

Turnbuckle Safety Wiring Tips-

Before safetying a turnbuckle, the cable must have the correct tension and there must be more than three threads showing on either side of the turnbuckle barrel.
When inspecting a control cable turnbuckle for proper installation, the safety wire ends should be wrapped a minimum of four turns around the terminal end shanks. When a turnbuckle is properly installed there should be no more than three threads exposed from either side of the turnbuckle barrel, and it should safetied.

FLIGHT CONTROL CABLE SIZE TYPE OF WRAP SAFETY WIRE DIAMETER MATERIAL
1/16 Single 0.040 inch Brass
1/8 Single 0.040 inch Stainless Steel
1/8 Double 0.040 inch Brass
5/32 Single 0.057 inch (min) Stainless Steel
5/32 Double 0.051 inch Brass

Turnbuckles Tips-
Some manufacturers of turnbuckles incorporate a “witness hole,” in the turnbuckle barrel to ensure that the threaded cable terminals are screwed in far enough into the barrel. The “witness hole” can be inspected visually, or by using a piece of safety wire as a probe.
To ensure that a turnbuckle develops full cable strength, there must be no more than three threads of either end sticking out of the turnbuckle barrel. After cable tension is adjusted, the turnbuckle barrel is safetied to the two cable ends so that it cannot turn. Different thicknesses of safety wire are available to safety different sizes of turnbuckles. For example, turnbuckles on 1/8 inch cable are safetied with a single wrap of 0.040 stainless steel or Monel safety wire, or 0.057 diameter copper or brass wire. Forty thousandths-inch copper or brass wire can be used if the turnbuckle is double-wrap safetied. Turnbuckles on 5/32 inch control cable can be double-wrap safetied with 0.040 stainless steel wire ore 0.051 copper or brass, or they may be single wrapped with 0.057 stainless steel wire.

Double-Wrap Spiral Method-
Of the methods using safety wire for safetying turnbuckles the method described here is preferred, although either of the other methods described are acceptable.
Step 1. Use two separate lengths of wire. Run one end of the wire through the hole in the barrel of the turnbuckle and bend the ends of the wire toward opposite ends of the turnbuckle.
Step 2. 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.
Step 3. Then pass the wires at the end of 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.
Step 4. 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.
Step 5. When a swaged terminal is being safetied, pass the ends of both wires through the hole provided in the terminal for this purpose and wrap both ends around the shank as previously described. 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 previously described. Another satisfactory double-warp method is similar to the previous method, except that the spiraling of the wires is omitted as shown in figure (B).

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