Reusing AN nuts and bolts?

Hi,

I've got a new-to-me 750 STOL sitting in my shop for a few months now. I just received a dual brake kit and have been installing that and hope to have the plane out to an airfield shortly. 

The wings are off for transport and to fit it in the shop. 

I have the nuts and bolts that were holding the wings and struts on with the plane. I had always intended on replacing all the nuts and bolts with new when I reattach the wings, but I'm now wondering if that might be overly paranoid. From what I can find there is no hard guidance on what to do, but I might just be bad at searching. I've seen opinions from never reuse to reuse everything as long as it looks ok and the nyloc is still retaining with enough force)

What are your thoughts? The plane has about 30 hours on it, so everything is fairly new. 

I see a few options:

  1. Replace all nuts and bolts (original plan)
  2. Replace all nuts only due to nyloc being used 
  3. Replace all nuts and inspect / replace bolts that look suspect (potentially new plan, but I'm not confident that it's clear what a good / bad bolt looks like)
  4. Reuse everything

Overall it's not that expensive to replace everything in the grand scheme of things, but wondering now if that's what people generally do?

Thanks!

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Permalink Reply by Darrell Doerhoff on February 20, 2022 at 7:15am

Nick,

Someone more knowledgable than me will probably chime in here, but it's my practice to replace locknuts in any place that, if it comes loose will be a safety issue. I think your wing attachements fall into this category.

I teach a high school aviation class, and in one lesson, I have the students study the crash of Galloping Ghost at the 2011 Reno Air Races. The NTSB concluded that reused locknuts contributed to this crash that killed several people.

Permalink Reply by Don Morrisey on February 20, 2022 at 9:10am

I believe that AC43.13 states nylon lock nuts can be used 3 times.  However how would you ever keep track of that over time?  For the cost of a new nut you can have peace of mind.  Personally I never reused a locknut, always a new one.  Since you will be remounting the wings and they'll probably be staying on for a long time, I would replace all the bolts too.  Bottom line is you don't know if the previous owner was reusing hardware, so I would definitely go with new.

Permalink Reply by Daniel Niendorff on February 20, 2022 at 10:43am

My practice is not to reuse nylock nuts.  There is a spec on the ability to reuse them - but my recollection is that it is cheaper and easier to just keep a stock of common size nylock nuts and replace them.  I don’t recall how the spec stated to measure the remaining nylock holding drag,  but I do remember thinking it was a pain.  As far as bolts go, I believe the AN series bolts stretch ever so slightly when properly torqued (like many automotive head bolts) - once past a critical stretch the strength drops off extremely quickly……. So I would not reuse a bolt that has been torqued.  And that goes double if someone else did the torqueing - as overtorque can immediately compromise the bolt.  And overtorque is a common error.

Permalink Reply by Earnest Fontenot on February 21, 2022 at 8:24am

Nick,
I think your best source of information to help you decide is AC43.13. This can be downloaded for free from the FAA.

AC43.13-1B States:
"Fiber or nylon locknuts are constructed with an unthreaded fiber or nylon locking insert held securely in place. The fiber or nylon insert provides the locking action because it has a smaller diameter than the nut. Fiber or nylon self-locking nuts are not installed in areas where temperatures exceed 250 degrees F. After the nut has been tightened, make sure the bolt or stud has at least one thread showing past the nut. DO NOT reuse a fiber or nylon locknut, if the nut cannot meet the minimum prevailing torque values. (See table 7-2.)"

Taken from AC43.13-1B, Chapter 7, Section 4. NUTS, Paragraph 7-64 f. Found on page 7-11.
The prevailing torque values table is on the next page.

I went online to look up the definition of Prevailing Torque.
I found:
"Prevailing torque is the amount of torque needed to run a nut down a thread on nuts that are designed to resist self-loosening under vibratory forces."

Hope this helps,
Earnie

Permalink Reply by Tony on February 27, 2022 at 9:33am

Bolts can be reused as long as nothing is wrong with them (deep gouges, cracks, etc). Nylock nuts go in the trash after their first use.

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