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I'm assuming saftey wire is used near propeller assemblies where a lot of vibration occurs, or where the different speeds and altitudes aircraft are at could cause expansion or contraction based on temperature. Is that correct?

I'm also wondering the reasoning for routing them in this manner. Is it done this way to counter vibration so both bolts don't loosen? If one is going counter-clockwise due to vibration, I'm assuming it'd be tightening the other bolt or vice versa?

Safety wire diagram

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  • $\begingroup$ Related question $\endgroup$
    – DeltaLima ♦
    Commented Feb 22, 2017 at 8:31
  • $\begingroup$ "I'm also wondering the reasoning for routing them in this manner." What other way would you route them? Right now, it's routed so as to pull both bolts tighter. You could route them so as to tighten one and loosen the other, or to loosen both, but that doesn't sound like an improvement. $\endgroup$
    – Sophie Swett
    Commented Dec 18, 2017 at 22:19

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Safety wire (positive wire locking) is done in areas where there is a possibility of the bolt getting loose due to vibration (also in other critical areas); this is done in a way such that the loosening of the bolt is counteracted by the tension in the wire i.e. in case the bolts loosen, the locking wire becomes taut and prevents further movement of the bolt.

Safety wire

safety wire examples; image from www.stangtv.com

There are different ways of doing wire locking for locking depending on the number of fasteners involved, but the basics are the same.

Safety wire

Safety wires; image from FAA AC 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair

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  • $\begingroup$ The text of this answer only mentions bolts. It is worth noting that safety wire is also commonly used to secure nuts and other hardware. $\endgroup$
    – J W
    Commented Feb 22, 2017 at 17:59
  • $\begingroup$ @JonathanWalters Also oil filters. Stupid oil filters.... $\endgroup$
    – voretaq7
    Commented Feb 22, 2017 at 18:12
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    $\begingroup$ @voretaq7 Yes, very true. But you know you could just get rid of the oil filter and go back to the oil strainer. The O-320 does superbly with the old style oil strainer and requires no replacement of the safety wire when reinstalling after cleaning (just a new gasket and four new lock washers). $\endgroup$
    – J W
    Commented Feb 22, 2017 at 18:17
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    $\begingroup$ The screen on my O-360 requires safety wire, because Lycoming hates you and wants you to be miserable. (It's also buried, because you're not having fun if you're not bending your arm in 6 different directions trying to get to the back of the stupid engine, which is why it only gets looked at during the annual.) $\endgroup$
    – voretaq7
    Commented Feb 22, 2017 at 18:52
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Air Force we safety wired everything that had the openings for the wire. If we could we would have safety wired the paint on. Jet aircraft also wore safety wire,

The joke was everything had safety wire so the accident inspectors could find all parts and put the aircraft back together! The real reason was to keep nuts and bolts from backing off and disengaging rendering the repair useless. All moving parts had to be safety wired if a part had four bolts or nuts and bolts not only were the bolts and nuts wired but the part itself got wired.

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    $\begingroup$ Please consider editing and polishing your answer. As it stands now it is a bit difficult to read. $\endgroup$
    – Federico
    Commented Dec 18, 2017 at 11:54
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    $\begingroup$ Welcome! Sounds like you had a lot of experience applying safety wire. If you could add details on why it was routed the way it was, that would help answer the question. $\endgroup$
    – FreeMan
    Commented Dec 18, 2017 at 13:03
  • $\begingroup$ Safety wire is used to keep parts from vibrating apart, it also keeps nuts and bolts from loosening from take offs and landings as well as turbulence in the air. Some parts on aircraft create vibrations on their own when the function. (Like hydraulic pumps) it also keeps lines from slipping off! $\endgroup$
    – user27635
    Commented Dec 23, 2017 at 13:08

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