Mohit Aggarwal Factory Acceptance Test Skill
A FAT is the last moment a defect is the factory's problem instead of yours. This skill writes the plan (or the report) with the parts that actually get argued over at the line: which spec clause each test covers, how many units get pulled and at what AQL, what exactly fails a lot, and who signs — so acceptance is a decision with a name on it, not a vibe at the end of a factory visit.
What This Skill Produces
- A test coverage matrix mapping every test to the spec requirement it verifies
- A sampling plan (ANSI/ASQ Z1.4) with lot size, inspection level, and AQL per defect class
- Unambiguous pass/fail criteria and lot accept/reject rules
- Golden-sample handling procedure
- A deviation log format and a sign-off block with authority levels
Required Inputs
Ask for these if not provided; if the spec is thin, draft the matrix from the product description and mark rows [spec clause to confirm]:
- Product and spec — the requirements document or at minimum a feature/claims list
- Lot size — units in the lot(s) under acceptance
- Product risk profile — safety-relevant? battery? affects AQL choice
- Prior quality history — first article vs mature product (allows tightened/reduced inspection)
- Who signs — customer QE, factory QA, third-party inspector?
Sampling & Classification Framework
Defect classes and default AQLs (ANSI/ASQ Z1.4, General Inspection Level II, normal inspection — the consumer-electronics defaults; adjust with reason):
| Class | Definition | Default AQL |
|---|---|---|
| Critical | Safety hazard, regulatory violation, data loss | 0 — any occurrence rejects the lot |
| Major | Product fails to function, or defect the user will certainly notice and return | 1.0 (tighten to 0.65 for premium/first lots) |
| Minor | Cosmetic or workmanship issue within limit samples' tolerance but noted | 2.5 (relax to 4.0 for bulk/industrial) |
From lot size + Level II, derive the sample-size code letter and accept/reject numbers from the Z1.4 tables; state them explicitly in the plan (e.g. "Lot 3,000 → code K → n=125; Major Ac=3/Re=4"). Switch to tightened inspection after 2 of 5 consecutive lots rejected; reduced only with sustained history.
Golden samples. Two signed, serialised golden samples minimum — one held at the factory line, one at the buyer. Sealed, dated, with an expiry/refresh rule (refresh on any ECO that changes fit/finish/function). Cosmetic judgement is against the limit-sample boundary set, never against memory.
Deviations. Any test performed differently than planned, any borderline judgement, and any use-as-is decision goes in the deviation log — numbered, with disposition and approver.
Output Format
FAT [plan | report]: [product] — lot [ID]
- Scope & lot definition — product rev, lot size, factory, date
- Test coverage matrix — table: test #, spec clause covered, method/equipment, sample basis (100% / AQL sample), pass criterion
- Sampling plan — lot size, code letter, n, and Ac/Re per defect class
- Pass/fail & lot disposition rules — accept / reject / rework-and-rescreen conditions
- Golden & limit sample register — serials, locations, seal dates, refresh trigger
- Deviation log — #, description, class, disposition, approver
- Results (report only) — defects found per class vs Ac/Re, failure detail with photos referenced
- Sign-off block — lot disposition, name, role, authority, date; rejection escalation path
Quality Checks
- Every spec requirement appears in the coverage matrix, or its exclusion is stated
- Sample sizes and Ac/Re numbers are explicit — not "per AQL 1.0"
- Critical defects have Ac=0 and an immediate-stop instruction
- Cosmetic criteria reference physical limit samples, not adjectives
- The report states defects per class against Ac/Re, and the disposition follows arithmetically
- Sign-off names a role with authority to reject the lot
Anti-Patterns
- Do not write "inspect to AQL 1.0" without the sample size and accept/reject numbers — that phrase settles nothing
- Do not let critical defects carry a non-zero acceptance number
- Do not judge cosmetics against memory or photos alone — physical limit samples or it will be relitigated every lot
- Do not allow rework-and-reinspect of a rejected lot without 100% rescreen of the reworked defect mode
- Do not accept a lot with an unsigned deviation in the log
- Do not let golden samples go stale across an ECO — refresh or they certify the wrong product