A layered process audit (LPA) is a short, frequent check of how a process is actually being run, done by people at several levels of the plant, from supervisor to plant manager. Each auditor asks a handful of questions at the machine, watches the work and records pass or fail. A failed answer is fixed or escalated on the spot. LPAs work because they catch drift between yearly audits, and because managers who audit regularly see the floor as it is.
What an LPA catches
Final inspection and the yearly system audit miss the daily drift: the work instruction nobody follows, the gauge that slipped past its calibration date, the setup shortcut that saves ten minutes. An LPA checks the controls themselves, often. It is not an inspection of parts. It confirms that the things that prevent defects are in place today.
Automotive customers often ask for LPAs after a quality problem or as a standing requirement, and AIAG publishes a guideline on them (CQI-8). Ask your customer what they expect before you design yours.
Who audits, and how often
| Layer | Who | A common frequency | Focus |
|---|---|---|---|
| 1 | Team leader or supervisor | Every shift or daily | Setup, tools, gauges, work instruction followed |
| 2 | Area or production manager | Weekly | The same questions, plus whether layer 1 is really auditing |
| 3 | Quality or engineering manager | Weekly or monthly | Controls, changes, containment, open findings |
| 4 | Plant manager | Monthly | A few questions and the open findings list |
This is a common pattern. Set yours by risk. The higher layers do not ask harder questions. They ask the same ones and see different things. A plant manager at the machine is also the fastest way to get a finding fixed.
Where the questions come from
- The PFMEA and the control plan. Take the high-severity failure modes and the controls that guard against them. Each control becomes a question: is it in place and working today?
- Your complaints and escapes. Every corrective action that changed a process should add a question that checks the new control is still there. Field Book 1, chapter 7 covers this.
- Setup and special characteristics. First-off checks, gauge condition and the controls on the characteristics your customer cares about most.
- Last audit findings. What failed once is likely to fail again.
Write each one as a yes or no question that can be answered by looking. “Is the go/no-go gauge at the station and inside its calibration date?” works. “Is quality being maintained?” does not.
A ten minute audit
Pick the station and bring the sheet
Five to ten questions for that process, on paper or a tablet. Rotate through the processes so every station is covered over the cycle.
Watch before you ask
Stand at the station and watch a cycle. What you see is better evidence than what you are told.
Check the thing, do not ask about it
Read the gauge date, the setup sheet, the tag, the chart. Ask the operator to show you.
Record pass or fail on every question
Partly in place is a fail. Add a note and a photo for each one.
Fix what you can on the spot
A missing tag, a wrong tool or an out-of-date instruction gets fixed in front of the operator. Anything bigger goes to an owner with a due date.
Contain if parts could be affected
If a failed control could have let bad parts through, treat it as a containment event first. The containment guide sets out the difference between containing, correcting and fixing the cause.
When a question fails
A failed question is a finding, not a mark against the operator. Correct it immediately, record it and give it an owner and a date. If the same question fails again, ask why with a 5 Why, and check whether the control is realistic or the question is wrong. A finding with no follow-up teaches everyone to stop reporting.
What to track
- Completion rate by layer. If the plant manager layer is at 40 percent, the system is not working, and the shop floor can see that.
- Findings by question. The questions that fail most point at your weakest control.
- Time to close. Long-open findings are a management problem, not an operator problem.
- Repeat findings. A repeat means the fix did not hold. Go back to the cause.
Retire a question when its control has passed for a long time and has been verified another way, and replace it with one drawn from a recent complaint. A checklist that never changes turns into a ritual.
Sample checklist: bore operation on a CNC lathe
| # | Question | How to check |
|---|---|---|
| 1 | Is the work instruction at the station and the same revision as the document list? | Compare the revision to the master list |
| 2 | Is the bore gauge at the station and inside its calibration date? | Read the calibration sticker |
| 3 | Was a first-off part measured and recorded after the last setup? | Check the signed setup sheet and the values |
| 4 | Is the offset change log current for this shift? | Compare the log to the last tool change |
| 5 | Are control chart points plotted, and has any out-of-control signal been acted on? | Read the chart |
| 6 | Is suspect material in the red tag area and tagged? | Count the tags against the log |
| 7 | Is today’s coolant concentration check recorded? | Check the log |
| 8 | Are finished parts going into the right tote with dividers? | Watch a pack out |
| 9 | Can the operator say what to do when the gauge reads out of tolerance? | Ask them to show you |
| 10 | Is the reaction plan posted and readable? | Look at the station |
The Layered Process Audit workbook gives you the layers, schedule and findings tracking in one file, if you would rather not build your own.
Questions people ask
How many questions should an audit have?
Five to ten. If it takes more than about ten minutes, it will get skipped when the day gets busy.
Can an operator audit their own station?
A self-check is useful, but it is not an audit. Layer 1 is usually a team leader or supervisor looking at someone else’s work.
What is the difference between an LPA and an internal audit?
An internal audit is planned, periodic and done by a trained auditor against a whole process or system. An LPA is short, frequent and done by management layers against a small set of controls.
Does my customer require layered process audits?
Many automotive customers do, in their customer-specific requirements or after a quality escape. Check yours.
What if people are too busy?
Start with one process, five questions and layer 1 only. Add layers once the first one is running and producing real findings.