A common issue that arises when installing safety wire is that since the manual skill required to implement traditional safety wire is easily learned, the techniques required to maximize the tension of the safety wire (e.g., in which direction the tension should be exerted, the direction of twist, proper angles for securing multiple fasteners, proper twists per inch, which type of wire to use, etc.) are often ignored by non-formally trained technicians who use safety wire for their projects.
We firmly believe that the techniques needed to tie safety wire can be acquired with the proper information and practice. Safety wire is a type of locking device that prevents fasteners from loosening or falling out due to vibration and other forces. The presence of safety wiring may also serve to indicate that the fasteners have been properly tightened.
Safety wire is available in a variety of gauges and materials, depending on the application. In aircraft applications, stainless steel wire is used. Typically, the wire is threaded through a hole drilled into a fastener or part, then twisted and anchored to a second fastener or part, then twisted again.
If you use safety wire properly, then you will be able to secure any nut, bolt, etc. on your aircraft so that vibration will not cause it to loosen during operation.
Choosing the Correct Plier
The easiest way to install safety wire to your aircraft is by using safety wire pliers. A new product that we highly recommend is the Milbar® 7W TigerWave ™ Safety Wire Twisters. The 7W TigerWave™ has some great features that make using this safety wire twister a true joy. It features a “smooth wave grip” to prevent nicks and scratches on the safety wire as the previous serrated grip used to cause. FOD (foreign object debris) prevention is always a major concern when installing safety wire so Milbar has included a cushion throat to catch any debris that falls during this process.
We will go into detail about certain kinds of safety wire pliers throughout this article. Safety wire pliers come in three common sizes: 6, 9, or 12 inch. Along with the different options for sizing you can choose whether to use a standard or reversible twister as well.
Standard twister pliers come in left or right handed versions depending on which way you prefer to twist the safety wire. When choosing a plier you will also come across an automatic return or manual return. The automatic return features a spring that retracts the twist rods to ease and speed up the work, whereas, the manual return does not.
Another nice option to have on your pliers is the cushion throat which catches clipped wire ends and prevents FOD within your aircraft’s engine compartment. Smaller length pliers offer a tapered or diagonal nose as well to fit the users preference.
You can also purchase a reversible twister which allows the option to use both left or right handed twisting. Offering two nose configurations, tapered and diagonal, gives the user flexibility amongst projects.
As the standard twister pliers have, the reversible models also have the automatic spring return as well as the cushion throat to catch loose clippings as they fall.
Considerations Before Installing
AVWeb.com gives some great procedures to consider before installing:
- Use new safety wire for every application.
- Do not tighten so much that vibration could break the wire.
- Do not over-twist; twists should be tight and even.
- Create a “pigtail” of ¼” to ½” at the end of the wire run.
- Tighten castle nuts to the low side of the specified torque range unless otherwise specified.
- Apply the wire so that any pull from the wire tightens the nut, not loosens it.
Installation of Safety Wire
Once you have chosen the correct safety wire plier for your specific job, you will want to begin by grabbing the two loose ends of the wire and locking the plier on these two ends. Once the two ends are firmly grasped by the nose of the pliers, pull the knob and release the pliers with your opposite hand, allowing the pliers to twist the safety wire. Perform this action until the wire is securely twisted as shown in the video below.
When using the Double Twist Method (Aerospace Standard AS567) you will want to be sure to understand a few key points. First, the maximum span of safety wire between tension points is only 6”, so do not stretch it too far and do not use more than 24” per application. Second, when looping the wire around the outside of a fastener, always route under the wire protruding from the hole. Third, do not make your pigtail too long; it should be no more than ¾”. Lastly, the number of twists per inch (1 twist= ½ complete turn) depends upon wire diameter:
- 0.020”to 0.025” diameter= 8-14 twists
- 0.032″ to 0.041″ diameter= 6-11 twists
- 0.051″ to 0.060″ diameter= 4-9 twists
Whichever safety wire plier you choose, be sure to always follow the standards. These proven methods have been tested over multiple decades and can be the difference between you flying safely or not.
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