# 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
- **FMD-91** (RAC/DTIC) — *Failure Mode / Mechanism Distributions* — modes +
  mechanisms with **% distribution (α)** per part class. **Public domain**
  ("Approved for Public Release; Distribution Unlimited"). DTIC ADA259655.
- **NPRD-91 / NPRD-95** (RAC/DTIC) — *Nonelectronic Parts Reliability Data* —
  field **failure rates λ** for mechanical / electromechanical parts. **Public
  domain.** DTIC ADA242083.
- **MIL-HDBK-217F** (US DoD) — electronic-part failure-rate models λ. Public
  domain (obsolete 1995 but legally free).
- **Attribution:** `Source: FMD-91 / NPRD-91 (RAC, DTIC), public domain`
- **AVOID:** Quanterion NPRD-2023 / FMD-2016 / EPRD-2024 (proprietary reissues),
  OREDA (commercial), FIDES tables (© DGA — read-only), ISO 14224 (copyrighted).

## 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.