# Are lockwires still preferred over self-locking nuts and other ways of bolted joints safety?

I've watched some of the lockwiring videos and if I understood it right then there are two most widely used ways of ensuring that a bolted joint does not get loose:

Difficulties and costs of maintaining the lock-wiring are obvious. My intuition says it only has to be used as a last resort when no other way is available. Nevertheless any aviation junk yard says my intuition is wrong. Lock-wires are everywhere in the old gas turbine engines. My question is:

Do they now use other methods of bolted joints safety in gas turbine engines (jam nuts and locking washers in particular)?

• Are you asking exclusively about turbine engines, or about aircraft in general? Also, are you asking about new designs, or about latest maintenance practice on equipment of any vintage? Nov 25 '16 at 15:59
• @JonathanWalters My curiosity is not limited :) The more information on the topic i.e. "bolted joint safety in aviation" the better. Not historical information but the current trends, achievements and standards. Dec 5 '16 at 10:14

Difficulties and costs of maintaining the lock-wiring are obvious. My intuition says it only has to be used as a last resort when no other way is available. Nevertheless any aviation junk yard says my intuition is wrong. Lock-wires are everywhere in the old gas turbine engines. My question is:

Do they now use other methods of bolted joints safety in gas turbine engines (jam nuts and locking washers in particular)?

Well, maintaining safety lockwire isn't as hard as you think it is: A pair of safety wire pliers will last you a lifetime, and they do about 80% of the work for you (all the maintenance monkey needs to do is cut an appropriate length of wire, hook up the pliers, and twist, making sure the wire is positioned so as to always tighten the fastener).
It is easy to inspect, repairing is simple (just replace the damaged wire), and cost for a spool of wire is minimal compared to using a new self-locking nut every time something needs to be taken apart (safety wire earns its keep for temporary assembly too: You can wire the assembly when you're done, rather than wearing the lock material on a self-locking nut).

Other methods of securing fasteners are used on aircraft (in engines and elsewhere), including cotter pins and self-locking nuts with nylon inserts to prevent them from slipping. The cotter pin is easy to verify (like safety wire), and is widely used. Self locking nuts on the other hand can slip without much visual indication (torque seal or similar products are often used to mark the nut and fastener to give a visual indication of slip).

A disadvantage to self locking nuts is that they must be replaced any time the fastener is removed (reused nuts will have a lower locking resistance, and may fail to hold), and using them introduces a potential for human error in maintenance operations that does not exist with safety wire, which must be cut to remove it. (There are even folks who try to reuse cotter pins, though normally they are cut to remove them and thus cannot be reused.)

• Hi. Thank you for the information. Is my reading of your answer as: "No, lockwire and self-locking nuts are still the main ways to provide bolted joint reliability in aviation in 2016`" correct? Dec 5 '16 at 10:28
• Do you have a reference for a requirement to replace self locking nuts after every removal? That is not necessarily industry practice and I am not aware of such a requirement. There are lots of cases where non-critical components, such as engine baffling, are secured with self locking nuts. Dec 5 '16 at 14:29
• @JonathanWalters Recommendations vary on reuse: I know the air force requires self-locking nuts in "critical areas" to be replaced every time they're undone, but I believe they allow reuse in non-critical areas (cosmetic attachments, etc.). FAA AC43.13-1B allows reuse of self-locking nuts if the running torque is within a specified limit range, and if it's lower than that the nut must be replaced as the insert is too worn to provide security. At my (non-aerospace) job we have bags of nylock nuts & just replace them each time though: We're lazy and thats easier. Dec 8 '16 at 20:02
• @voretaq7 Ok, those are the advisories I had in mind. We typically reuse nuts in non-critical locations, but replace in locations such as control surface applications. A lot of aircraft applications also use fully metal self locking nuts, especially in engine applications, and these seem to wear less than nylock nuts. Dec 8 '16 at 20:08

Lock wires are the most basic of maintenance. I being a maintenance person use lock wire every where and every nuts and bolts possible.

I haven't analyzed the financial part of using it but I would say it is the most safest means of securing because it cannot be loosened unless you cut the wire but self locking nuts are sometime found defective. Other means such as securing with tap washer or spring washer are also less effective compared to lockwires as the tap washers can slip sometimes and you may not have noticed it. Hence, unless it is impossible to use lockwire or its very difficult at the moments; It is always recommended to use lock wire wherever possible.

• Do you work with the relatively modern engines or the older ones? Your answer is clear but what is your field? Dec 5 '16 at 10:31
• I am currently working with LET 410 UVP- E20 Turboprop aircraft, I am in the engineering department; maintenance guy basically. And as far as I know even the Airbus Aircraft extensively use lock wires. For, the connecting hoses there isn't going to be an alternative for lock wires. Dec 7 '16 at 13:40