Anchor Nut substition

[sph33r]

Good evening all,
I was wondering, if you guys could share your knowledge... its a two pronged question, actually...
a. how acceptable is it to swap out an anchor nut with a lock nut, and if so is his given anywhere as standard practice?
b. how applicable are general standard practices to an aircraft when its own technical manual has its own standard practices?
I understand they may be totally naive, silly questions but... none the less I would appreciate any answers...

[dixi188]

a. Usually ok to use an equivalent stiff nut if an anchor nut has failed and then record it so that it can be replaced at next major hangar input. Probably find a ref. in Standard practices of the SRM. Done it many times on things like Windscreens and Antenna.

b. Manufacturers manuals take precedence over any general maintenance guidance. The UK CAA withdrew CAIPs, (Civil Aircraft Inspection Procedures), back in the 80s to stop people using generic stuff. Shame, as there was lots of good info in there. The FAA AC43 is only useable if there is no manufacturer published applicable information.

[sph33r]

Thanks dixi, if I recall FAA 43 states that in order to replace one type of nut with another, you must contact FAA or manufacturer.
Can you point me to where its stated in print that manufacturers standard practices overrule general standard practices?
I've burned through the manufacturer manuals and it doesn't say anything about substitution of nut types between them...

[NutLoose]

I don't know if this helps

https://www.faa.gov/documentLibrary/...C_23_607-1.pdf

https://www.faa.gov/documentLibrary/...r/AC_20-71.pdf

https://www.easa.europa.eu/sites/def...eners_PUBL.pdf

[sph33r]

Thanks Nut,
nothing in there precisely fits the situation, but thanks for the effort.

[wrench1]

Originally Posted by sph33r

Good evening all, I was wondering, if you guys could share your knowledge... its a two pronged question, actually...

Which regulatory system? Don't know if this is what your looking for, but here’s the FAA side. However, without more details on the anchor nut/locknut swap I can only give a general reply.

a. how acceptable is it to swap out an anchor nut with a lock nut, and if so is his given anywhere as standard practice?

It is perfectly acceptable to substitute hardware under the FARs provided it follows several requirements. And it’s technically considered an alteration vs a standard practice. How easily the fastener can be swapped depends on if the original installation data is FAA approved or FAA acceptable data, and if the hardware swap is considered a major or minor alteration. Regardless how complicated the latter sounds, a majority of hardware substitutions are considered minor alterations with acceptable data.

The go-to reference that allows the substitution is FAR Part 43.13(a) linked below. It gives the path to pursue with emphasis on the underlined statement after the bolded “or”. That latter statement opens up a large source of guidance docs to include “standard practice docs, specifications docs, etc. But keep in mind which FAR the aircraft is maintained under may also tweak the hardware swap criteria as well.

(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. […]
Part 43.13(a)

A simple example. Aircraft comes with screws installed on a panel that gets removed on a regular basis. You want to replace the screws with bolts due to screw tip wear. You look up the specs for the screws and bolts to see if they are equal or if the bolts are stronger. You then determine if the hardware swap is a major or minor alteration which in this case is a minor. The mechanic swaps out the screws with bolts under a simple logbook entry.

b. how applicable are general standard practices to an aircraft when its own technical manual has its own standard practices?

It depends on what FAR the aircraft is maintained under and if the hardware substitution is defined as a minor or major alteration. But in general Part 43.13(a) allows you to use whatever FAA acceptable reference you want. Without the specific examples it’s tough to give any better references.

[sph33r]

Thanks Wrench, I'll study into the material you linked once the turbocharged toddler is asleep, regarding details...
It is a State registration aircraft, so it is not monitored by an aviation authority outside the military and since the substitution is authorized by said military authority it is legal (within the organization, in any case). What I am trying to find is -since it is not mentioned as an option within the manufacturers technical documentation- the general concept in the industry, of how acceptable it is as a practice...And if there is any logic to the arguments "if we can do it on one aircraft type why cant we do it on another" and "there are general standard practices that apply to everything, everywhere" (I believe reading Part 43 will cover me on these matters, from an FAA perspective, I wonder what EASA would say...)
From a technical standpoint, as long as there is the same "force" holding everything in place, and the nut is secured I understand there shouldn't be an issue.
The anchor nut in question (1 of 6) supports a bracket, which in turn supports the flotation gear.

[Tom Sawyer]

If there is no substitution detailed in the AMM or SRM, usually I'd pass this on to the airline engineering (CAMO) department. They usually have access to more in depth manuals and information, and if suitably approved as a design organisation could issue a temp repair authority with details of what can be used, for how long and any supporting requirements (additional or periodic inspections etc) and use the authority reference to raise a DD based on the details.

[dixi188]

Make sure the fasteners are of the same material as the original . If there is any Titanium around make sure there is no Cadmium plating on the fasteners.
Had a big repair on a DC-10 engine pylon years ago when someone had used Cad. plated Hi-Locks on a mod.

[sph33r]

Tom Sawyer that's pretty much the path that was taken, eventually. There was alot of info thrown around, none of which in ink which is why i asked here, judging I had better odds at a solid answer...
dixi188 Im pretty sure the bracket that the nut tightens on to is aluminum, although there is definitely titanium in the area. But its something I'm gonna run by the guys that did the repair...thanks!