# Failure-consequence & maintenance decision logic — NASA RCM (public domain)

Drives the IACE auto-FMEA "recommended action" layer and the safety-priority
rule. Ingested into `bp_iace_fmea_kb`.

## Source
- **Source:** NASA — NPR 8831.2F Ch.7 (Reliability-Centered Maintenance) and NASA GSFC-HDBK-8004 (FMEA & Risk Assessment)
- **License:** US Government work — **public domain** ("cleared for public accessibility")
- **Attribution:** `Source: NASA NPR 8831.2F / GSFC-HDBK-8004, public domain`
- **Retrieved:** 2026-06 · **Ref:** nodis3.gsfc.nasa.gov / standards.nasa.gov

## Safety-consequence priority (key rule)
A failure with a **safety** consequence is prioritised **regardless of how rare
it is** — "safety shall be ensured at any cost; thereafter cost-effectiveness
becomes the criterion." So in a SAFETY FMEA a single Catastrophic mode matters
even at low occurrence — severity dominates the ranking.

## Failure definition (broad)
"Any unsatisfactory condition" — loss of FUNCTION **or** loss of QUALITY/
acceptable performance — not only complete breakdown. (Captures drift,
degradation, intermittent.)

## Recommended-action decision logic (RCM)
| Failure character | Recommended task |
|---|---|
| Gives advance warning / measurable degradation | **Condition-based / predictive** monitoring |
| Age/wear-related, predictable | **Preventive / scheduled** replacement |
| Random, low consequence | **Run-to-failure** (corrective) |
| Hidden / no effective task | **Redesign** or add **redundancy / detection** |

This maps onto the IACE 3-step measure hierarchy (inherently safe design →
safeguarding → information) for the FMEA's control/action column.

## How used in IACE
- Safety-priority rule overrides pure Cm ranking when the linked ISO 12100 hazard
  is high-severity (the safety-FMEA bridge).
- The decision table seeds the recommended-action suggestions per failure mode.

Concepts only — IEC 61508/ISO 13849 (SIL/PL, DC, β-factor tables) are copyrighted
and NOT reproduced; diagnostic-coverage / common-cause are used as generic ideas.