Good Morning, I'm hoping to get

[daxmann]

Good Morning,

I'm hoping to get some input from other engineers that have done Liaison engineering work in aerospace. I just completed my disposition on a discrepant item that changed a couple of nut-plates on a nut-strip because of mis-drilled holes. The last instruction in the disposition was to re-identify the part using the Non conformance report (NCR) number with a -1 at the end. This has been common practice in the other aerospace companies I have worked but it got me thinking when do I have to change the part number with a repair and when don't I.

I have completed countless repairs over the last 29 years and the overwhelming majority do not require the changing of the part number for the NCR. Is a fit, form and function issue? All the repairs change the form in some way but most don't require a part number change to identify the NCR.

Does anyone know of a good rule of thumb that is reliable for this issue?

 

[rb1957]

i'd say that if you make a new part, well it needs an ID; but if you rework a part then the NCR number should be stamped on it.

another day in paradise, or is paradise one day closer ?

 

[daxmann]

Reworking a part means bringing it back to drawing requirements so changing the PN is not required but repairing means deviating from the original engineering in a way that is still acceptable to engineering. In the case above I changed the type on nutplate used for 2 of the 4 on the nut strip and therefore needed to change the PN. My confusion is I have added or subtracted nutplates (as well as other hardware) on assemblies before and not changed the PN.

Is there some sort of rule that states when the PN must be changed?

 

[WKTaylor]

daxmann...

1. I concur with RB1957 "...if you rework [or alter] a part then the NCR number should be stamped on it.".

2. Variation...

It is one of my primary functions to redefine an old-out-of-production part/Assy for '1-off' local manufacturing purposes. For these parts I go one-step farther IF/AS needed. IF my disposition allows multiple alloys/tempers [example: wrought/machined parts substituting for cast/machined parts], I mandate application of the NCR number followed by the alloy/temper of the material actually used by the shop.

3. Another Variation...

In some cases, material substitution dispositions are specifically requested by the design group, or the NCRs are taken by the design group, and incorporated onto the drawings. In these cases, the policy stands that each newly-defined part requires new/unique -#s. These [new PNs] are then entered on the effectivity block with a flag note stating they are preferred spares for [old -#s]. Eventually these new PNs end-up in the IPB as substitutes for the old PNs.

4. This process has been complicated over the years, due to various 'engineering administrative' factors.

A. Older [low cost/'simplified'] practices allowed the final drawing and original PNs to be 'simply updated' with flag notes specifying the alternate material/process. Talk about configuration control nightmares. Example: Mag castings/machining's with mag finishes, were changed to cast or wrought aluminum with aluminum finishes with no PN changes at all. In some cases the new materials/processes were made mandatory by dates [as-of XXYYYZZZZ do this...] so spares procured after that date 'should conform'. However, in most cases, contracting was forced to do the engineering job and specify the alternate materials/processes per FLs XX, YY, ZZ, etc.

B. Better practice evolved that if fit-form-function-material-finish changes occurred, the PNs/effectivities were 'rolled' [discrete PNs and effectivities] for each configuration.

C. Current CAD practices have also affected documentation practices. In-lieu of adding a new [CAD] sheet [W/ new PNs] to an old [hand-] drawing... and updating the PL... the latest CAD procedures dictate new drawings [W/ new drawing and -# numbers] for each configuration. Works great for new/in-production acft and for big organizations with electronic book-keeping... but is a nightmare for long-out-of-production acft with low production spares-rates and tight budgets.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[SkipVought]

I'd think that a factor to consider is the maintainability and the supply logistics.

If a repaired is required for this assembly in the field, the necessary support must be documented and available.

Skip,
[sub]
Just traded in my OLD subtlety...
for a NUance![/sub]

 

[rb1957]

"Is there some sort of rule that states when the PN must be changed?" I think there's company practice as much as an "rule".

In your example I'd reidentify the part, but I can see that the change is minor enough that stamping the part with the NRC would give enough of a paper trail as to why this part is different. This is the point ... we have to be able to separate documented "official" repairs from "unofficial" repairs; the latter being a real problem for our industry).

another day in paradise, or is paradise one day closer ?

 

[crackman]

See FAA Advisory Circular AC 43-18. Page 7 describes the requirements for part marking. This AC is for the manufacture of parts as part of a major alteration or repair.