Aerospace Cpk Requirements

How is capability handled in a low-volume, high-mix, contractually controlled environment where AS9100, Key Characteristics and First Article Inspection dominate?

• Use the contractual and customer-specific requirement for each key characteristic.
• Define the study window, sigma estimator, reaction plan, and alternative controls.
• Do not substitute a generic Cpk target for product-safety or special-process validation.

AS9100 and AS9102 do not specify a numeric Cpk. Capability targets on aerospace parts are set by contract, by Key Characteristic flow-down (typically AS9103) and by customer engineering. Special processes may fall under Nadcap accreditation. Low-volume, high-mix production makes traditional long-run SPC impractical; short-run SPC and configuration control dominate.

1. Extract contractual capability requirements and KC/CC classification before any measurement.
2. Complete FAI per AS9102 for the applicable configuration baseline.
3. For KCs, apply short-run SPC (e.g. standardized Xbar-R or Individuals) with normalized targets.
4. Record configuration ID, operator, machine, and traceable material lot on every measurement.
5. For special processes, ensure Nadcap or customer accreditation is current before study.
6. Route non-conformances through MRB with disposition traceable to the contract.
7. Update capability baseline on configuration change — not on a fixed calendar.

• KC on drawing not translated into shop-floor SPC.
• Configuration mismatch between engineering, planning and inspection.
• FAI closed on partial data; delta FAI not triggered on change.
• Special process operated outside accredited parameters; capability still reported.
• Traceability broken between raw material heat, part serial, and measurement record.

• Aerospace capability failures are usually configuration failures — the wrong drawing revision was in production.
• Short-run SPC on standardized data is far more useful than long-run Cpk on aggregated part families.
• KC flow-down that stops at the top-level drawing is the most common audit gap.
• Nadcap findings frequently expose that capability data was collected outside the accredited process window.

• Do not compute long-run Cpk on low-volume high-mix production without normalization.
• Do not report capability without a locked configuration baseline.
• Do not use capability data as substitute for FAI — they are complementary, not interchangeable.

• Capability vs FAI: FAI demonstrates configuration; capability demonstrates repeatability. Both required.
• KC vs standard characteristic: KCs require ongoing monitoring; standard characteristics may not.
• Special process capability: Only valid inside the accredited parameter window.

Use the free Process Capability Calculator to compute Cp, Cpk, Pp, Ppk, sigma level, and predicted PPM from your measurement data — no sign-up required.

• Never begin a capability study without confirming configuration baseline and revision.
• Never accept short-run SPC without a documented normalization method.
• Never claim capability on a special process operated outside its accreditation envelope.

• ✓KCs and CCs identified from drawing and contract
• ✓Configuration baseline locked and referenced
• ✓FAI (AS9102) complete for the baseline
• ✓Short-run SPC method documented for low-volume KCs
• ✓Special-process accreditation current and within envelope
• ✓Traceability chain intact: material → part → measurement → record
• ✓Non-conformance disposition routed through MRB

• Process condition: statistical stability is required.
• Distribution assumption: use a distribution model justified for the data.
• Confirm process stability and measurement-system adequacy before interpreting a capability index.
• Use a justified distribution model or non-normal method when the normal model is unsuitable.
• Numerical targets shown on industry pages are common examples, not universal requirements. The contract, drawing, customer-specific requirement, Control Plan, and validation protocol take precedence.