Engineering designation of critical parts

[Ng2020]

Context - I am in a growing startup design/manufacturing environment. No Production Cert.
Note: we do fixed wing airplanes, not rotorcraft - an important distinction because of
27.602/29.602.

Currently our engineering drawings & process specs do not explicitly identify critical parts, nor do they provide direction for manufacturing to conduct specific inspections on such details.
One of our Manufacturing Eng's is from a rotorcraft background and is interested in identifying each critical part in the BOM so that affected work instruction cards get 2x QA signatures.

In your collective experience:
1. is this standard practice in your org.? If so how are critical parts typically identified on the engineering drawings?
This seems like a trivial question, but I don't recall seeing this practice in other organisations. If it was happeneing, it wasn't commonplace or immediately apparent.

2. What are the Manufacturing/ QA implications of such a designation in your organisation ? does this designation purely relate to ensuring serialisation/marking of critical parts under Part 21, or does your organisation impose additional inspection criteria?

Apologies if these questions seem a bit half baked. hopefully this will provoke some good discussion which will yield answers to questions I haven't even thought about yet.

 

[SWComposites]

Critical parts are rare, just those needing extra inspections/QA/etc over and above your normal production QA system and engineering requirements. Engine mounts for instance.

From one company I have experience with, drawings state "Critical Part per Process Spec XYZ", where the referenced process spec has the requirements for a critical part.

Implications? the extra paperwork and inspections for the part.

Tell your ME you don't have any critical parts.

 

[WKTaylor]

Every company that I'm aware-of... that NEEDS to designate a part as 'manufacturing/flight critical'... has written/numbered policy document(s) or drawings or Flag Notes, that explicitly state fabrication criteria... A-to-Z... for the raw material, drawing quality, manufacture-inspection-certification [to spec], installation, tracking [Part/Serial Number]... etc. AND these parts are identified in the AMM for mechanics and in company proprietary/unique documents for internal use.

BUT be aware, once a part is 'labeled' with this 'critical' status costs and documentation skyrocket. Usually only specific qualified raw-stock, manufacturers-people-equipment- etc have been vetted... changes to any element may require a MAJOR/INDEPTH 're-do of everything for qualification'.

On my old jet there were few such parts for the last 60-years. New generation designers, analysts, M&P, etc tend to default to greater/critical controls... especially when modern materials and processes change the nature of part fabrication... such-as... 'was' a die forging: now machined from forged block or plate, alternate materials, etc... even if margins are high. Sighhh.

Have fun.

 

[rb1957]

Are you making your own parts, or re-making other people's parts ?