# Failure-mode taxonomy & reliability data — FMD-91 / NPRD-91 (public domain)

Open component→failure-mode taxonomy and failure-rate (λ) / mode-ratio (α)
anchor for the IACE auto-FMEA. Ingested into `bp_iace_fmea_kb`. The bulk numeric
tables are fetched from the DTIC PDFs in a follow-up P1 step; this doc fixes the
sources + the per-component mode lists used to seed the gated library (P2).

## Sources & licence (CORRECTED 2026-06-12 — NOT public domain)
- **FMD-91** (RAC/DTIC, ADA259655) and **NPRD-91/95** (RAC/DTIC, ADA242083) carry
  **"© 1991, IIT Research Institute. All Rights Reserved."** + DoD "Approved for
  public release; distribution unlimited". The distribution statement allows us to
  OBTAIN/READ them; it is **NOT** a licence to reproduce the tables in a commercial
  product. Treat exactly like DIN/ISO: **do not reproduce the tables, do not bulk-
  ingest them.** Their successor (Quanterion) sells the data commercially.
- This doc therefore reproduces **no FMD-91/NPRD table** — only a GENERIC failure-
  mode taxonomy (general engineering knowledge / CC-BY-SA Wikipedia) and source
  pointers. The λ/α numeric tables are **NOT vendored**.
- **MIL-HDBK-217F** (US DoD employee work) — electronic-part λ models — **is**
  public domain (genuine DoD standard).
- **AVOID reproducing:** FMD-91/NPRD-91 tables (© IITRI), Quanterion NPRD-2023 /
  FMD-2016 / EPRD-2024 (proprietary), OREDA (commercial), FIDES tables (© DGA),
  ISO 14224 (copyrighted). Never use any of these "in conjunction with the name"
  of the US Government or IITRI without written permission.

## Failure modes by component class (open — FMD-91 + CC-BY-SA Wikipedia)
| Component class | Typical failure modes |
|---|---|
| Bearings | fatigue spalling/pitting, wear, brinelling, seizure, contamination |
| Gears | pitting, scuffing/scoring, tooth-fatigue fracture, wear |
| Shafts / fasteners / springs | fatigue fracture, fretting, loosening, set/relaxation |
| Seals / hoses / cylinders | leakage (external/internal), extrusion, hardening, rupture |
| Valves / pumps | stuck-open, stuck-closed, leakage, fail-to-open/close, degraded flow |
| Motors / contactors | winding short, open circuit, insulation breakdown, contact weld/stick |
| Sensors / cabling | drift/bias, loss of signal, intermittent, open/short |

FMD-91 additionally gives the **% weighting (α)** of each mode per class — that
is the mode-ratio in `Cm = λp·α·β·t` and lets the engine RANK modes rather than
enumerate them flatly.

## How used in IACE
- Taxonomy → seeds/expands the gated failure-mode library (P2).
- λ (NPRD/217) × α (FMD-91) → mode rate → `OccurrenceFromRate` → 1–10 occurrence.
- Each `source`/`license` tagged; allowlist rejects copyrighted/proprietary data.
