PPAP Element 11 Initial Process Studies: What Ppk Value Passes and Why Reviewers Reject the Number Before They Read It
Element 11 is where the statistical work of a PPAP package either holds up or collapses. A reviewer's-seat walkthrough of Initial Process Studies under AIAG PPAP 4th Edition: why initial studies report Ppk and not Cpk, the three-tier acceptance criteria at 1.33 and 1.67, the two prerequisites a reviewer verifies before trusting your index, the significant production run sample rules, the non-normal and one-sided characteristic trap that voids a clean-looking number, five kickback patterns, and a pre-submission QA pass you can run in fifteen minutes.
Cpk vs Ppk: Which Process Capability Index to Use for PPAP
Cpk and Ppk measure process capability differently and are not interchangeable on a PPAP submission. Here is what each one measures, which sigma each uses, and what PPAP Element 11 actually requires.