GD&T - Specific Tolerance Requirement vs. Critical Item vs. Key Characteristic



Dear all,

greetings from turkey and sorry for my baby english,

I would like to ask difference between 3 definitions are given below.
These definitions are given on FMEA training presentation prepared by Airbus people,
I have no doubt with KC, but i don't have much experience with STR and CTI

Specific Tolerance Requirement (STR)
A Specific Tolerance Requirement is a feature within the product, which does not have a proven significant impact on the product?s performance, requiring specific attention throughout the development of the product.
STR are monitored at least during development phase.

Critical Item (CtI)
A Critical Item (CtI) is a Product / Process feature which non conformance to specification has a significant impact regardless where they seat within
tolerance range.
CtI are monitored during both development and serial phases. ( Traditional Loss function )

Key Characteristics (KC)
A Key Characteristic is a Product / Process feature where variation (departure from nominal) has a significant impact on the product.
KC are important features which results shall be as near to
the nominal value of the tolerance.
KC are monitored using Statistical Process Control (SPC) :
? Process Stability
? Cp/Cpk Process Capability ≥ 1.33
The KC shall be inspected 100% as long as the conditions are not fulfilled. ( Taguchi loss function )

Thank you in advance for your support
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