Control Plans and PPAP: How Manufacturing Quality Gets Locked In Before Production Begins

What PPAP is and why customers require it

Before a supplier ships production parts to a customer for the first time, the customer needs confidence that the supplier’s process will consistently produce conforming parts — not just that the sample parts submitted for approval are acceptable, but that the process that made them is capable and controlled. PPAP provides that confidence through a structured evidence package. Rather than relying on the supplier’s verbal assurances or on inspecting every incoming part, the customer reviews documentary evidence that the supplier has analyzed the design, planned the process, validated the measurement systems, demonstrated process capability, and established ongoing controls.

The PPAP requirement is most rigorously applied in automotive supply chains under IATF 16949 (the automotive extension of ISO 9001), where customers such as Ford, General Motors, and Stellantis specify PPAP as a contractual requirement for new part numbers and for changes to existing parts. Non-automotive customers in aerospace (AS9100), medical devices (ISO 13485), and defense often impose equivalent requirements under different names (First Article Inspection, Initial Sample Inspection Report, Qualification Test Report), but the underlying logic is the same: demonstrate process validity before production begins.

The 18 PPAP elements

The AIAG PPAP reference manual (currently in its fourth edition) defines 18 elements that make up a complete PPAP submission. Not all 18 are required for every submission; the customer specifies a submission level (1 through 5) that determines which elements must be submitted versus retained at the supplier. The 18 elements are:

1. Design Records — the engineering drawing or model that defines the part’s requirements. For a customer-designed part, this is the customer’s drawing; for a supplier-designed part, the supplier provides it.

2. Engineering Change Documents — any authorized engineering changes incorporated in the design that are not yet reflected in the formal design record.

3. Customer Engineering Approval — documented evidence that the customer’s engineering organization has approved the part when required.

4. Design Failure Mode and Effects Analysis (DFMEA) — required only for supplier-responsible designs; documents potential failure modes at the design level and their detection and prevention controls.

5. Process Flow Diagram — a schematic showing all process steps from raw material receipt through shipping, including inspection steps and rework loops.

6. Process Failure Mode and Effects Analysis (PFMEA) — the process-level FMEA that identifies potential failure modes at each process step, their severity, occurrence, and detection ratings, and the controls in place.

7. Control Plan — the document that operationalizes the PFMEA by specifying, for each controlled process step, what is measured, how, at what frequency, and what to do when a measurement is out of specification.

8. Measurement System Analysis (MSA) — gauge R&R studies and other MSA data demonstrating that the measurement systems used for product and process control are adequate (typically %GRR under 10 percent is preferred, under 30 percent is conditionally acceptable).

9. Dimensional Results — actual measurements of all dimensions on the engineering drawing from production-intent parts, with balloon numbers cross-referencing the drawing.

10. Records of Material/Performance Test Results — test results for all material certifications (hardness, tensile strength, chemical composition) and functional performance requirements specified on the drawing.

11. Initial Process Studies (Capability Studies) — Cpk and Ppk data for all Special Characteristics (designated critical or significant on the drawing and PFMEA). The AIAG standard requires Ppk of 1.67 minimum for initial submissions, transitioning to Cpk of 1.33 for ongoing production.

12. Qualified Laboratory Documentation — evidence that any laboratory performing testing is qualified (internal lab scope documents or external lab accreditation certificates).

13. Appearance Approval Report (AAR) — required only for parts with appearance requirements; documents customer approval of color, grain, gloss, and other visual attributes.

14. Sample Production Parts — physical parts from the PPAP production run, in the quantity specified by the customer (typically 1 to 300 parts depending on submission level and customer requirements).

15. Master Sample — a reference part retained at the supplier (and sometimes at the customer) that represents the approved design standard against which future production is compared.

16. Checking Aids — fixtures, gauges, models, or templates developed specifically to check the part; these are documented and retained.

17. Customer-Specific Requirements — any additional requirements specified by the customer beyond the standard AIAG elements.

18. Part Submission Warrant (PSW) — the cover document that summarizes the PPAP submission, signed by a supplier representative affirming that all elements have been completed and that the parts and process meet all customer requirements. The customer’s signature on the PSW constitutes formal PPAP approval.

PPAP submission levels

Customers specify a submission level that determines which physical elements must be sent to the customer versus retained at the supplier site for review upon request. The five levels are:

Level 1: Part Submission Warrant only (and, if required, an Appearance Approval Report). Minimal documentation sent to the customer; all other elements retained at the supplier. Used for standard commercial parts or very low-risk situations.

Level 2: PSW with product samples and limited supporting data. Used for less complex or less critical parts.

Level 3: PSW with product samples and complete supporting data package. This is the default level for most new automotive parts when no other level is specified.

Level 4: PSW and other requirements as defined by the customer. Used when the customer specifies a non-standard subset of elements.

Level 5: PSW with product samples and complete supporting data package reviewed at the supplier’s manufacturing location. Used for the most critical parts or when the customer wants to audit the process in person during the PPAP review.

Control Plans: structure and content

The Control Plan is the production quality management document that flows directly from the PFMEA. Where the PFMEA asks “what can go wrong and what controls do we have?”, the Control Plan asks “how exactly will we execute those controls on the production floor?” The Control Plan has three sections corresponding to the three phases of APQP: Prototype (for pre-production builds), Pre-Launch (for pilot runs), and Production (for ongoing manufacturing). Most ongoing quality management uses the Production Control Plan.

A Control Plan is organized as a table with one row per controlled process step or measurement activity. Each row specifies:

Process step: the operation number and description, cross-referenced to the Process Flow Diagram.

Product characteristics: what product feature is being controlled at this step (dimension, surface finish, material property, functional performance).

Process characteristics: what process parameters affect the product characteristic at this step (temperature, pressure, feed rate, cycle time).

Special characteristic designation: whether this characteristic is designated as a Special Characteristic (Critical, Significant, or customer-specific symbol) requiring enhanced monitoring.

Product/process specification and tolerance: the nominal value and tolerance from the engineering drawing or process specification.

Evaluation/measurement technique: the specific gauge, fixture, or test method used to measure the characteristic.

Sample size and frequency: how many parts are measured and how often (every part, every 30 minutes, every lot, etc.).

Control method: the statistical or procedural method used to monitor and control the characteristic (SPC chart, inspection record, attribute check, poka-yoke device).

Reaction plan: what the operator does when a measurement is out of specification or a control chart signals an alarm — containment action, notification, rework or scrap, process adjustment, and who is responsible.

Special Characteristics

Special Characteristics are product or process characteristics that the PFMEA and the customer’s engineering team have identified as having a disproportionate effect on safety, regulatory compliance, or downstream fit and function. Special Characteristics receive enhanced treatment throughout APQP: they drive the PFMEA’s focus, they require capable measurement systems (MSA), they must demonstrate high Cpk in the PPAP capability studies, and they receive more frequent or more rigorous monitoring in the Control Plan.

Customer-specific symbols vary: Ford uses an inverted triangle for Critical Characteristics and a diamond for Significant Characteristics; General Motors uses SC (Safety Critical) and CC (Critical Characteristic); Chrysler/Stellantis uses similar designations. The AIAG symbol is a shield shape. When working with multiple customers, suppliers must maintain a cross-reference between customer-specific symbols and their own internal designation system to ensure consistent treatment across programs.

When PPAP is required

PPAP is not a one-time event at the beginning of a program. Most customer requirements mandate a new PPAP (or at minimum a formal customer notification and approval) for:

• New part numbers being sourced to the customer for the first time.
• Engineering changes to an approved part — changes to the design record, tolerances, or material specification.
• Process changes at the supplier — new tooling, new equipment, new process sequence, or changes to key process parameters.
• Source changes — moving production to a different plant, adding a second manufacturing line, or changing a sub-tier supplier for a controlled characteristic.
• Production interruptions — if a process has been inactive for a customer-specified period (typically 12 months for automotive), a new PPAP may be required to restart.

Common errors in PPAP and Control Plan preparation

• Capability studies from pre-production tooling. PPAP capability data must come from production-intent tooling, equipment, and environment — not from prototype tools or development runs. Parts produced on temporary tooling do not validate the production process.
• Insufficient sample size for capability studies. A Ppk calculated from 10 parts is statistically unreliable. AIAG recommends a minimum of 25 subgroups of 5 parts (125 total parts) for initial capability studies, or a minimum of 100 consecutive parts for an Pp/Ppk analysis.
• MSA not performed on gauges used in PPAP measurement. Dimensional results and capability studies are only valid if the measurement system has been validated. Gauge R&R studies must be conducted on the same gauges used to generate the PPAP data.
• Control Plan not aligned with PFMEA. Every high-severity, high-RPN item in the PFMEA should appear in the Control Plan with a corresponding control. A PFMEA that identifies a critical process parameter but a Control Plan that does not monitor it represents a gap that customers and auditors will flag.
• Reaction plans that are generic or incomplete. “Stop production and call supervisor” is not a reaction plan. The reaction plan must specify disposition of nonconforming product, containment boundaries (how far back does the concern extend?), and escalation path.

Frequently asked questions

What is PPAP and why is it required?

PPAP (Production Part Approval Process) is a formal process used primarily in the automotive industry (and increasingly in other manufacturing sectors) through which a supplier demonstrates to a customer that its manufacturing process is capable of consistently producing parts that meet all engineering specifications. Customers require PPAP because they cannot cost-effectively inspect every incoming part, and they need evidence that the supplier’s process — not just an individual sample — is capable and controlled before production begins. A PPAP submission includes up to 18 elements of documentary and physical evidence: engineering drawings, process flow diagrams, FMEAs, a Control Plan, measurement system analysis data, dimensional results, material test results, process capability data, sample parts, and a Part Submission Warrant signed by the supplier. PPAP originated with the major North American automakers and is formalized in the AIAG PPAP reference manual. It is required under IATF 16949 and is a contractual requirement in most Tier 1 automotive supply agreements. Non-automotive customers may use equivalent processes under different names, such as First Article Inspection (FAI) in aerospace under AS9102.

What is a Control Plan and how does it relate to the PFMEA?

A Control Plan is a structured document that specifies, for every step in a manufacturing process, which product and process characteristics are monitored, what measurement system is used, how frequently measurements are taken, and what actions are taken when a measurement goes out of specification. The Control Plan is the production-floor operationalization of the PFMEA (Process Failure Mode and Effects Analysis): the PFMEA identifies potential failure modes, their causes, and the detection and prevention controls that should be in place, while the Control Plan specifies the exact implementation of those controls — the gauge number, the sample size, the SPC chart type, the reaction plan. A well-linked PFMEA and Control Plan should be cross-referenceable: every high-severity item in the PFMEA should have a corresponding row in the Control Plan, and every row in the Control Plan should be traceable to a process step in the Process Flow Diagram and a failure mode in the PFMEA. Misalignment between the PFMEA and the Control Plan is one of the most common findings in customer quality audits.

What Cpk or Ppk is required for PPAP approval?

The AIAG PPAP standard requires a minimum Ppk of 1.67 for Special Characteristics on initial PPAP submissions. For non-special characteristics, the minimum is typically Ppk of 1.33, though individual customers may specify higher minimums. The distinction between Ppk and Cpk is important in the PPAP context: Ppk uses the overall standard deviation from the entire PPAP run (capturing all sources of variation, including between-subgroup variation), while Cpk uses the within-subgroup standard deviation (an estimate of inherent process capability under stable conditions). PPAP requires Ppk rather than Cpk because the process has not yet been demonstrated to be in statistical control at the start of production. Once the process is in sustained production and demonstrably in control, ongoing monitoring shifts to Cpk with a minimum of 1.33. When initial capability data falls below the Ppk 1.67 threshold, the typical response is conditional approval with a requirement to submit a corrective action plan and provide updated capability data after a defined period of production. Full PPAP approval requires meeting the capability threshold.

What are Special Characteristics and how are they treated in the Control Plan?

Special Characteristics are product or process characteristics identified by the customer’s engineering team and the supplier’s PFMEA as having a significant effect on safety, regulatory compliance, or downstream fit and function if they fall outside specification. They are designated with customer-specific symbols on the engineering drawing and in the PFMEA. In the Control Plan, Special Characteristics receive enhanced monitoring: they typically require 100 percent inspection or statistical process control with control charts, rather than periodic sampling; they require capable measurement systems (gauge R&R under 10 percent preferred); and they require Ppk of 1.67 or higher on the initial PPAP capability study. The reaction plan for a Special Characteristic going out of specification is typically more stringent than for a general characteristic — often requiring immediate production stop, full lot containment, notification to the customer, and root cause analysis with corrective action. From an IATF 16949 audit perspective, Special Characteristics are where auditors focus most of their attention on the Control Plan, because they represent the highest-risk product and process features.

What triggers a new PPAP after initial approval?

Most automotive customer requirements mandate resubmission of PPAP (or at minimum formal customer notification and approval) for any change to the product or process that could affect form, fit, function, performance, or durability. Common triggers include: engineering changes to the part drawing or material specification; changes to the manufacturing process, including new tooling, new equipment, new process sequence, or changes to key process parameters such as temperatures or pressures; production location changes, including moving to a new plant or adding a second production line; sub-tier supplier changes for materials or components that affect controlled characteristics; production interruptions, where a process has been inactive beyond a customer-specified period (typically 12 months for automotive); and appearance changes for customer-visible surfaces. The Part Submission Warrant identifies the reason for submission, and the supplier must document what changed and provide evidence (new capability data, new dimensional results, updated Control Plan) to support the change. Implementing a process or design change without customer notification and approval, when notification is contractually required, is a serious supply chain nonconformance that can result in production disruption liability.

What is the difference between PPAP submission levels?

PPAP submission levels specify which elements of the PPAP package must be physically submitted to the customer versus retained at the supplier’s location for review upon request. Level 1 is the least rigorous: only the Part Submission Warrant (and Appearance Approval Report if applicable) is submitted; all other elements are retained at the supplier. Level 2 adds sample parts and limited supporting documentation. Level 3 is the standard default level for new automotive parts: the complete PPAP package including all applicable elements is submitted to the customer for review. Level 4 involves the PSW and other requirements defined by the customer, used for non-standard cases. Level 5 is the most rigorous: the full PPAP package is reviewed by the customer at the supplier’s manufacturing location, allowing the customer to examine the actual production equipment, tooling, and process in addition to the documentation. Higher submission levels are typically required for higher-risk parts (safety-critical components, new supplier relationships, or situations where the customer has had previous quality issues with the supplier or part family). The level does not change what must be completed by the supplier; it only changes what must be sent versus retained.