FMEA Worksheet

About FMEA

FMEA (Failure Mode and Effects Analysis) is the most widely used proactive reliability method in manufacturing: for every part of a system, list how it can fail (failure modes), what each failure does (effects), why it happens (causes), and how it is caught (controls). Each row is rated on three 1–10 scales — Severity, Occurrence, Detection — and prioritised. Standardised by AIAG-VDA FMEA Handbook (2019) and IEC 60812.

Schematex's edge is that the engine computes the priority, not just the table. It flattens the failure chain to one worksheet row per (item, mode, cause), computes RPN = S × O × D, and — crucially — the AIAG-VDA Action Priority (severity-primary banding), which deliberately fixes the bug a raw RPN sort introduces: an airbag failure at S10·O2·D3 is High even though its RPN (60) looks low.

1. Your first worksheet

Every document starts with fmea, an optional title, optional directives, then a nested failure chain. Structure comes from the keyword, not the indent depth:

fmea "Pump DFMEA"
  item "Impeller" fn "Move fluid"
    mode "No flow"
      effect "Process stops" sev: 8
      cause "Impeller wear" occ: 4
        controls detection: "Flow sensor" det: 5

• item "name" fn "function" — a part and the function it delivers. fn is optional.
• mode "failure mode" — how that function fails. An item may hold several.
• effect "consequence" sev: 1..10 — what the failure causes; carries its own Severity. A mode may have several (the engine uses the worst for every row of that mode).
• cause "root cause" occ: 1..10 — why it happens; carries Occurrence.
• controls prevention: "…", detection: "…" det: 1..10 — current controls and the Detection rating they earn. With no control, Detection defaults to 10 (undetectable).

All three ratings are integers 1–10; anything outside that range is rejected.

2. Header directives

type: design          # design (dfmea) | process (pfmea) | msr
rank: ap              # ap (default) | rpn — the sort/priority key
flag: ap >= High      # or `rpn > 100` — highlight rows over a threshold
number: FMEA-2026-014 # free metadata: number/team/author/date/revision/dept/process/product

rank chooses how rows are prioritised; flag highlights the rows that breach a threshold (ap >= High / ap == High, or rpn > 100 / rpn >= 120).

3. Computed RPN & Action Priority

This is the differentiator. From the nested AST the engine:

1. Flattens to one row per (item, mode, cause); the mode's worst effect severity governs every row of that mode.
2. RPN = S × O × D (1–1000).
3. Action Priority by the AIAG-VDA band structure — Severity is the primary axis, Occurrence second, Detection third. S = 9–10 (safety/regulatory) is High for every O and D; mid-severity degrades High→Medium→Low as Occurrence falls.
4. Sorts by the chosen key. For ap: High > Medium > Low, tie-broken by Severity then RPN — never RPN alone, which would re-introduce the bug AP was designed to fix.
5. Flags rows over the threshold.

Each row carries data-rpn and data-ap so the computed priority is inspectable.

4. After-action follow-up

Record corrective actions and the revised ratings to show the before/after delta:

fmea "Brake DFMEA"
  item "MC"
    mode "Seal leak"
      effect "Loss of braking" sev: 9
      cause "Degradation" occ: 3 det: 4
  action "Seal leak" / "Degradation"
    do: "Upgrade seal to EPDM" owner: "J. Lee" target: 2026-Q3
    revised sev: 9 occ: 1 det: 4

action "Mode" / "Cause" targets a chain by its quoted mode and (optional) cause; do: is the recommendation; revised sev/occ/det recomputes the after-action RPN and AP so the engine reports the risk reduction.

5. Common mistakes

# WRONG — rating out of the 1..10 band
effect "Leak" sev: 11

# WRONG — mode before any item
mode "orphan mode"

# WRONG — effect before any mode
item "x"
  effect "e" sev: 3

Ratings must be integers 1–10; the failure chain must nest item → mode → effect/cause; out-of-order keywords are rejected by name. Detection silently defaults to 10 if no control rates it — state det: (on the cause or its controls) when you have a detection control.

6. Standard compliance

The failure chain and the Severity/Occurrence/Detection scales follow the AIAG-VDA FMEA Handbook (2019) and IEC 60812. The Action Priority implements the published band structure (severity-primary), not the paywalled verbatim 1000-cell table. RPN remains available via rank: rpn for legacy worksheets.

7. Roadmap

Deferred: the exact AIAG-VDA AP/MSR decision tables, multi-effect-per-cause weighting, and structure/function-tree views.