Safety wiring

[Bruce Tuncks]

Can anybody provide an example where safety wiring has prevented an accident?

 

I am not really doubting that safety wiring is good etc. It is just that I don't know if it has ever worked as intended.

 

 

[facthunter]

How do you think it's intended to work? Nev

 

 

[Downunder]

Yes, I can provide an example. 

 

Every engine, every airframe, everyday, bolts do not randomly come undone.....

 

 

[rgmwa]

I think you're more likely to find examples of where not safety wiring has caused or contributed to an accident. If the safety wiring is effective, there won't be anything to see.

 

 

[facthunter]

 I must confess I prefer a tab washer. I think the lockwire enables a quick look to check that nothing has moved. The wire is not there to actually provide a significant tightening force It's unable to do that. At positions where there's lots of vibrations it's not likely to last that long either. Nev

 

 

[Thruster88]

All I know is Airtractors have lots of safety wire with the lugs placed in the most inaccessible positions with some other components placed to block our view. ? John Deere type tractors with very similar parts have no locking wire and nothing ever falls off. If I had to guess the force required to bust the lock wire is negligible on something like a fuel filter bowl. I think the real reason for lock wire is a final check of our own work and for others to check.

 

On a side note, one of my friend's  told me about an oil leak on the filter of a Rotax 912, from under the hose clamp that was used to attach the lock wire. It seems the hose clamp may have caused a small dent in the filter which caused a fatigue crack to develop. 

 

 

[Old Koreelah]

...an oil leak on the filter of a Rotax 912, from under the hose clamp that was used to attach the lock wire. It seems the hose clamp may have caused a small dent in the filter which caused a fatigue crack to develop. 

 

Interesting. I've been accused of being anal for installing a hose clamp and lock wire on my oil filter.

 

It makes me feel better, but I never thought it could cause an oil leak.

 

 

[facthunter]

 Most failures of those filter casings are a manufacturing fault. I've never seen a properly tensioned filter move till you try to get it off. Big end bolts today have NO form of locking other than the tension applied.  Some have coating for a one use lock function.( Suspension and brake components).   My wife's Lawnmower uses the same filter as a jabiru. does  (now) it's cheaper than the US made original (which is probably better for the Jabiru as well. Nev

 

 

[M61A1]

Can anybody provide an example where safety wiring has prevented an accident?

 

I am not really doubting that safety wiring is good etc. It is just that I don't know if it has ever worked as intended.

 

I have seen the three bolts that hold the lower engine mount on the accessory case of a C250 installed on a Bell 206 loose and only held by the lockwire. Whether they were never torqued on installation, had worn inserts or came loose during operation I will never know, but I can tell you that when the lockwire was removed, the bolts were easily removed with fingers. 

 

 

[spacesailor]

I,ve Never seen Both ends of a nut & bolt lock-wired! .

 

If you lock none end, whats to stop the other end turning,

 

Locktite type nut locker will allow the bolt to turn without it parting company with the parent part.

 

Test it yourself & undo the other end of the lock-wired fastner.

 

spacesailor

 

 

[facthunter]

You wouldn't use  lockwire with a "free"nut on the other end, unless it was "captive". You would use a castellated nut with suitable pin or the various lock nuts available depending on the heat about the area. Nev

 

 

[M61A1]

I,ve Never seen Both ends of a nut & bolt lock-wired! .

 

If you lock none end, whats to stop the other end turning,

 

Locktite type nut locker will allow the bolt to turn without it parting company with the parent part.

 

Test it yourself & undo the other end of the lock-wired fastner.

 

spacesailor

 

Like Nev  says, you wouldn’t use lockwire in that situation. That’s a job for a split pin, self locking nut or both. A lot of flight control bolts have both nylon and a split pin. F111 ones had a ball locking device that was operated when to pushed an Allen key in to drive it and a split pin which both prevented the nut from turning and the ball loch being actuated. 

 

 

[Yenn]

If a lockwired nut came off it would have been incorrectly wired. The object of the lock wire is to prevent the nut turning. It has to be applied with rotation in mind.

 

 

[facthunter]

A lockwire has very limited ability to resist a nut turning, in my view.  If you were in a hurry you'd snap them easily by just undoing the nut or bolt by driving a ring or socket over the wire and undoing the particular fitting. Yes they are supposed to be fitted in  regard to the direction they unwind being immediately noticed as the wire would have to break, before the Bolt moved any real distance. It is NOT any guarantee the bolt has been torqued to the right setting. that's often done with a dob of (usually) yellow paint but that's not foolproof either. I think lockwiring provides a  visual check nothing has moved since it was lockwired and not a lot else. Nev

 

 

[spacesailor]

"If a lockwired nut came off it would have been incorrectly wired."

 

OR

 

The Bolt at the other end unwound, Leaving that Wired Nut dangling.

 

spacesailor

 

 

 

 

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Posted 4 h

 

 

 

 

 

 

 

[Yenn]

Surely the ability to withstand turning would be the breaking strain of the wire multiplied by the radius of the flat of the nut. A not inconsiderable amount compared with the force trying to undo the nut.

 

 

[facthunter]

It's actually a force of a very small order compared with the torqueing force and any force required to undo most nuts that are not loose, already.  You only have to break one of the two wires through the bolthead. On a filter it's got a much bigger radius, To be fair many locking devices don't have a lot of strength in their own right. A split pin and castellated nut often permit adjustment, and the nut is not tight at all. Some others have a preload and may be pinned or staked into a groove to lock them. Nev

 

 

[spacesailor]

Vibration is the culprit, that moves objects, including nuts & bolts.

 

Vibration is used in industry to sort parts into order, looks like magic when watching things move without being touched by human hand.

 

spacesailor

 

 

[facthunter]

 "Good vibrations" are magic.. Harmonics in springs will eventually break them if you don't damp them. (Two stroke exhausts in aeroplanes). Nev

 

 

[turboplanner]

I attach a two stroke exhaust by sliding it into a spigot bolted to the cylinder and holding it there by three coil springs. Solves the problem of cracks and backfires.

 

 

[facthunter]

And there's some black gloop you squeeze onto the springs to stop them moving and eventually breaking. Nev

 

 

[derekliston]

Just an , I hope interesting aside. Back when I was a 16yr old apprentice (1963) I had the opportunity to explore two RAF transports at Edinburgh Turnhouse airport. One was an Armstrong-Whitworth Argosy, the other was one of the first RAF C130s. I will not forget noticing that every single hydraulic fitting on the Argosy was lockwired and electrically bonded. The C130 by comparison didn’t have a lockwire or a bonding strip to be seen. All of the unions were, I found out later, Parker flareless couplings, which, I am glad to say was also the norm on B707 and B747 at BOAC when I joined in 1968.

 

 

[skippydiesel]

And there's some black gloop you squeeze onto the springs to stop them moving and eventually breaking. Nev

 

The "black gloop" I use is high temperature silicon but I also safety wire the springs, in the event that the spring brakes there is less chance of a part "flying" loose in my engine compartment.

 

 

[Hargraves]

Ask any pilot of a pusher configured aircraft what lockwire value may be and you,ll probably get a definitive (must have) and no doubt from them especially concerning exhaust pipe hv silicon coated retaining springs and other items.

 

 

[Hargraves]

I have twice found broken but retained exhaust pipe springs during one daily and one preflight check. That may well not count as preventing an accident but it sure prevented and damage occurring to the prop. I carry spare springs and HT silicon in both my storch and my 500 as a result.