Defective Standard Hardware - MS21042, NAS1291 self-locking nut failures 5

[Metalsmythe1977]

Has anyone been up to speed on the defective MS21042/NAS1291 self-locking nuts being reported due to improper cad coating processes?

Any wisdom from the Forum would be appreciated.

 

[thruthefence]

I've seen two failures in the field, both MS21042-4. The bolts were loaded in shear, and the torque putty was still intact. Scarey stuff when the helicopter drive train is full of this stuff.

 

[WKTaylor]

MS21042 & NAS1291 steel nuts are susceptible to hydrogen embrittlement. Heard that a certain lot of 1/4-28 steel nuts are suspect [made by a specific manufacturer].

The NAS1291C*M nuts [A286, Passivated + SFL] should be a fool-proof alternative.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[etsosie]

Note: there is no problem going to NAS1291 except that if your design is dependent on the strength of MS21042. With the use of NAS1291, expect an axial strength reduction. Might be more helpful to seal the attach points and cover. I do suspect the hardware installation might have to do with it. Over Torquing and Torguing Pattern is always a problem.

 

[WKTaylor]

Just recieved confirmation for USAF Source that there is a major HE problem with MS21042-6 Nuts with Mnfctr code "EN" ... not MS21042-4 nuts.

What is highly unusual is that these nuts were in use on an aircraft wheel assy... which is very odd. I would have expected to see A286 or I-718 HS wheel nuts with solid film lubricant, such as NAS1804L6, NAS1805L6, NAS1757, NAS1758, NAS1759.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[dgapilot]

There have been several cases of cracks in MS21042-6 nuts in the Navy. There is a lot with a raised "EN" marking and if I recall correctly all the failures were in this lot.