AIAG-VDA Action Priority calculator

What Action Priority is

Every line of an FMEA carries three scores from 1 to 10. Severity is how bad the effect of the failure would be. Occurrence is how often its cause is expected to happen. Detection is how likely your current controls are to miss it. Action Priority, usually shortened to AP, turns those three scores into one of three answers: High, Medium or Low. It tells the team which lines deserve engineering time first.

AP arrived with the AIAG-VDA FMEA Handbook in 2019 and is used for both process and design FMEAs. It took over the job that the Risk Priority Number had done for decades, and it did so because RPN was sending teams to the wrong lines.

Why it replaced RPN thresholds

RPN multiplies the three scores together, giving a number from 1 to 1000. A company then picks a threshold, commonly 100 or 150, and requires action on anything above it. The flaw is in the multiplication: it treats the three scores as interchangeable, and they are not.

Take two lines. The first has a severity of 9, an occurrence of 5 and a detection of 2, for an RPN of 90. The second has a severity of 2, an occurrence of 5 and a detection of 10, for an RPN of 100. A threshold of 100 demands action on the second, a minor nuisance that nobody catches, and waves through the first, a serious failure that happens regularly. Action Priority calls the first one High and the second one Low. You can load both into the calculator: 9, 5, 2 and 2, 5, 10.

The second problem is human. Once everyone in the room knows the number that triggers an action, scores start to drift until the product lands just under it. A result that depends on the combination of scores, with no running total to nudge under a line, leaves much less to bargain with.

How the three scores combine

The calculator does not multiply anything. It places each score in a band and reads off the answer for that combination, in a fixed order of importance: severity first, then occurrence, then detection.

• Severity leads. A failure with a severity of 1 is always Low, whatever the other two scores say. At the other end, a severity of 9 or 10 with an occurrence of 6 or more is always High, however good detection looks.
• Occurrence comes next. When occurrence is 1 the result is Low even at a severity of 10, because the cause is effectively prevented.
• Detection settles the close calls. With a severity of 9 or 10 and an occurrence of 2 or 3, weak detection gives High, middling detection gives Medium and strong detection gives Low.

The result card shows which band each of your scores fell into, so you can see what drove the answer rather than taking it on trust.

What to do with each result

High means act. The team agrees an action that makes the cause less likely or the failure easier to catch, with an owner and a date. If no action is taken, the reason the existing controls are judged adequate is written down, and it should be a reason you would be comfortable reading out to a customer.

Medium means action is expected, with more room for judgement. Improve prevention or detection, or record why the current controls are enough.

Low means action is optional. Take the cheap improvements and move on.

Two cautions. Action Priority ranks where to spend effort; it is not a measure of how risky the product is, so Low does not mean safe. And your customer or your own procedures can ask for more than the method does. Many companies have management review every High or Medium line with a severity of 9 or 10, and customer-specific requirements can demand action on a line whatever its priority.

Getting scores worth calculating

The answer is only as honest as the three numbers behind it. Score against your written rating scales, whether those are your company's or your customer's, and bring data to the table. Occurrence should come from scrap, yield, nonconformance and warranty history wherever it exists. Detection should come from a hard look at whether today's control would really catch the failure. Record the reasoning for any score somebody challenged. There is more on running the study well in a PFMEA that engineers will actually use.

After an action is complete, score the line again and rerun it. The aim is for occurrence or detection to move, since severity rarely changes without a design change. The High and Medium lines should then show up as controlled characteristics in your control plan.

Common questions

Is Action Priority the same as RPN?

No. Both start from the same three scores, but RPN is their product and AP is a decision rule based on their combination. Many teams keep RPN alongside AP for continuity with older records, which is why the calculator shows both.

Does it work for a design FMEA?

Yes. The same priority logic applies to design and process FMEAs; only the meaning of the scores differs, as covered in DFMEA vs PFMEA. The supplemental method for monitoring and system response (FMEA-MSR) uses different inputs and is not covered by this calculator.

Is anything I enter stored?

No. The calculation happens on this page, in your browser. The three scores are held in the page address so that you can copy a link to a result. The reference and notes fields are used only on your printout and are never added to the link.

Not sure which problem-solving tool fits the failure you have found? The free tool selector is on the Axiom homepage.