Ntsb report on P51 Crash in reno 1

[berkshire]

The NTSB claims deteriorated lock nut inserts as part of the cause of the reno crash.
I am not aware that nylock or fiber insert nuts deteriorate on their own.
Does anybody have any info on that.
Or is this a case where mechanics re used the locknuts?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[MikeHalloran]

The detailed report:

http://www.ntsb.gov/doclib/reports/2012/AAB1201.pdf

specifically cites evidence of reuse, negligible locking torque, and general looseness.

Figure 14 suggests that the locking material was 'red fiber'.
Does that contain nylon? I don't know, but I know that some alcohols dissolve some nylons.
I have to wonder if methanol boiled off from the evaporative engine cooling system might have attacked the locknuts. ... not that a couple decades of reuse wouldn't loosen 'em up a bit anyway.




Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

Could be reuse, or maybe they got some solvent or something on them they shouldn't have.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[KENAT]

Oops, didn't see your post Mike. Looks like there was almost nothing of the insert left it had been reused so many times over 26 years.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[berkshire]

Mike,
the report you had was much more detailed than the one I had, which was just a summary.
Over the years as an aviation mechanic, I have always been told that the red fiber inserts were for one time use only, but that nylon inserts could be used a couple of times. This never did explain the use of fiber insert captive nuts in things like access panels, where after several uses you had to unrivet and replace the things because they did not hold anymore. This looks horribly like one of those " we will change it next time " scenarios.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[thruthefence]

This is simply a case of the most basic tenets of aircraft maintenance and inspection being ignored, in lieu of shiny polished aluminum, esoteric engine modifications, and operational hubris (or ignorance).

There is NOTHING that will kill you more surely then slop in an elevator tab, and few things that are easier to detect and rectify.

I bet more time was spent touching up paint on the aircraft's "Galloping Ghost" artwork, then was spent touching, moving, & inspecting the flight controls.

The rule of thumb on self locking fasteners, is that if they can be threaded on by hand, toss 'em. And this is fiber and metal lock nuts.