MIL GRADE AXEL BOLTS NUTS WASHERS

[G-MDAY]

Hi Ive been on the Forum and tried to get information re the correct bolts / fastners to use
for my new .... old Solid aluminium Axels (Still to arrive with me) as Im fitting the 8:50 Dresser Tundra tires

Well ive been confused before but this search was a real eyeopener

Anyway for those that may follow in my footsetps .....

Here's the Numbers you need for the MIL Grade Stuff
Bottom Bolts MS20006-31 3/8
Top Bolts MS20005-32 1/4
Countersunk washers MS20002C5
Countersunk washers MS20002C6
Stiffnuts MS21042-6
Stiffnuts MS21042-5

There not super cheap and the Nuts and washers come with minimum orders of 50

[GAHorn]

Do you have an Illustrated Parts Catalog? Do you have access to AN and NAS hardware?

You might contact Genuine Aircraft Hardware….as they are Assoc’n supporters and they retail the appropriate bolts, nuts, washers.

https://www.gen-aircraft-hardware.com/

[G-MDAY]

Hi George i was able to find a supplier in the UK LAS in Devon England
they sourced all the Bolts nuts and washers as per my list these fittings are all ugraded to
MIL strength and are the latest parts ie for the application of Big Wheels re FAA recommendations.

I have also Sourced Solid Aluminium Axles part No 0541124-1

Now looking for Castle Nuts and Split pins

Thanks again George

[GAHorn]

BE CAREFUL … about substituting aircraft hardware. Be aware that one cannot simply rely on a “MS” or “MIL” part number to be a correct replacement part.

The following is the applicable Text from an aircraft accident (Cessna 170B, NTSB report ANC02LA034 ) which suffered landing gear failure due to the improper substitution:

“ Accident investigation report completed and information captured
Narrative:
The right main landing gear leg separated from the airplane while landing on a gravel airstrip, which resulted in substantial
damage to the airframe. The main landing gear had recently been rebuilt, and this was the second landing since the work
was completed. The gear leg had been secured to the airplane with an AN7-20A bolt and an MS21044C stainless steel nut.
The bolt, which remained attached to the separated gear leg was bent and the threads were damaged. The MS21044C nut
had fractured, and was found in the right main landing gear bulkhead assembly. Examination of the nut determined it
fractured due to circumferential overstress tension. The airplane manufacturer's parts catalog specifies a AN365-720C steel
nut to secure the main landing gear legs. The military standard, under which the original AN365 nut was manufactured,
requires any substitute nut to be of like material, plating, and thread size, and specifically excludes the substitution of the
MS21044C nut in lieu of the AN365-720C nut. The proper substitute for the AN365-720C is the MS21044N, which is an
all steel nut. However, the rated tensile strength of the AN365, MS21044C and MS21044N series nuts are all 125 ksi.
Examination of the bolt revealed sheared threads adjacent to the bolt grip, indicating that the nut was intact on the bolt
when the bolt/nut combination was loaded to failure. The bending deformation of the bolt indicated a side load was present
during the failure. This side load could have resulted from a hard landing with the airplane moving sideways or improper
reinstallation of the landing gear may have allowed normal landings to introduce side loads.
Probable Cause: The separation of the right main landing gear from the airplane during landing. A factor associated with
the accident is the unapproved hardware used to attach the main landing gear.”

[DaveF]

This is the second time you've posted this and I still don't understand what it's saying about AN365 vs MS21044.

The report says "The proper substitute for the AN365-720C is the MS21044N, which is an all steel nut." Not according to any MS21044 spec I've been able to find. They all say the MS21044 is nylock. Is that a proper substitution?

AN365-720C is cad plate, but MS21044C is stainless. If there's a lesson in parts substitution here, it's that C doesn't signify stainless in AN365-720C.

[c170b53]

Thanks Dave, that report was certainly a mixed up, mixed message. I think it’s trying to suggest the cause was due to the difference between steel to stainless (malleability) and points out that the nut must not have a nylon insert. Then goes on to suggest the failure was really due to improper maintenance combined with a bad landing. Essentially cover all angles and move on.
I know seasoned owners know this but I’ll mention (one more time ),( for new members ) I do check my gear leg attachment on annuals because I’m very capable of a bad landing and AN hardware in tension is ductile. Bolts stretch, tension is reduced and stress risers form, leading to failure. Won’t happen in two flights hence the mx angle but certainly will exist if it goes undetected over time. The tail spring/tailwheel attachment exhibits this phenomenon but its in plain view, whereas the main gear is always loaded and the main attachment bolt hidden hence the importance of check it and also checking M/G shim health.

[GAHorn]

This is the second time you've posted this and I still don't understand what it's saying about AN365 vs MS21044.

The report says "The proper substitute for the AN365-720C is the MS21044N, which is an all steel nut." Not according to any MS21044 spec I've been able to find. They all say the MS21044 is nylock. Is that a proper substitution?

AN365-720C is cad plate, but MS21044C is stainless. If there's a lesson in parts substitution here, it's that C doesn't signify stainless in AN365-720C.

The “lesson to be learned” …in my opinion…is to be especially wary when substituting “equivalent” parts.
NTSB is comprised of especially talented investigators….but they are human …and I believe they sometimes miss what an ordinary person might not. (look up the fuel selector valve story I reported on in The 170 News…(1st Qtr 2011) …where NTSB reported that the improper assembly per the IPC of a fuel valve resulted in fuel-stavation…. when, in-fact, such improper assembly results in the Opposite Effect…. fuel cannot be Shut-Off.)

In the case of the landing-gear bolt/nut, I noticed that the (improper) corrosion-resistant MS21044C nut which failed was installed on a plain steel AN bolt. Dissimilar metals simply don’t “get along” for several reasons, but that dissimilarity was not mentioned.
The message I think NTSB was attempting to point out that the specified corrosion resistant AN365-720C nut…. which was replaced with a corrosion resistant MS21044C nut … was actually not an identically-designed replacement. The actual, approved replacement was a MS21044N nut…and perhaps the installer “assumed” the “C” would be the critical nomenclature feature.

The bottom line I think….Again… Beware of substituting parts.

And another thing… Regardless of the nut-failure…a Pponk landing gear beef-up kit would likely have prevented that failure entirely.

[G-MDAY]

All as mentioned are direct replacements for the original specifications
Non are stainless steel non are nylock all are as per manufacturer details
Slightly higher grade as per MIL specification allied to the FAA recommendations
For fitting Tundra Style tyres ie inclusion of periodic NDT on axles into the maintenance
Regime for the aircraft and use of higher specification fittings and fasteners and increased
Visual inspection etc

I think I’ve gone belt and braces to the max here as the likely hood of me landing on anything other than a grass runway are very remote (we cannot land just anywhere in the UK) but just trying to keep to the essence of the advisory from the FAA

Regards
Paul

[cessnut]

Not to beat a dead horse here, but according to my understanding an MS21044N nut is not a replacement for an AN 365-720C. It is a replacement for an AN 365-720. The bottom line is that the NTSB missed the fact that Cessna calls for an all metal locknut. Any Nylon nut, corrosion resistant or otherwise, would not be an approved substitute. Textron also gets this wrong since they superseded both AN 365-720 and AN 365-720C to an MS21044N.

[johneeb]

All.......

I think I’ve gone belt and braces to the max here ......
Regards
Paul

Translation for you yanks "belt and suspenders"

Wobbles : You know you can trust me.
Frank : Wobbles, how can you trust a man that wears both a belt and suspenders? Man can't even trust his own pants.

[G-MDAY]

Here’s a quick question ? How did we end up talking about ….. MS21044N I never mentioned it in my original post ….

[GAHorn]

Here’s a quick question ? How did we end up talking about ….. MS21044N I never mentioned it in my original post ….

It was in my post above…wherein I copied the NTSB Accident Report on a Cessna which used inappropriate substitute hardware.