Safety Case Documentation - Functional Safety (ISO 26262)

The Safety Case: Structured Argument

Definition

A safety case is a structured argument, supported by evidence, that the item is safe for its intended use. It must demonstrate that each safety goal is satisfied by showing:

The hazards are correctly identified (HARA)
The safety goals are correct and complete (HARA output)
The system design meets the safety goals (FSC, TSRs, SSRs)
The implementation is correct (reviews, tests, analyses)
The residual risk is acceptable (PMHF, SPFM, LFM)

Goal Structuring Notation (GSN)

GSN Safety Case Fragment: AEB Safety Goal

  Goal G1 [ASIL-D]:
  'AEB system is acceptably safe with respect to SG-01
   (no unintended braking above 5 km/h)'
      │
      │ Strategy S1:
      │ 'Argument by demonstration that each
      │  contributing hazard cause is mitigated'
      │
      ├── Goal G1.1:
      │   'Inadvertent AEB from sensor fusion fault is acceptably safe'
      │   ├── Solution Sol-1.1.1: FMEA showing DC=97% for sensor faults
      │   ├── Solution Sol-1.1.2: SPFM=99.2% calculation report
      │   └── Solution Sol-1.1.3: HIL fault injection test VT-SG01-001 (PASS)
      │
      ├── Goal G1.2:
      │   'Software fault cannot cause unintended AEB'
      │   ├── Solution Sol-1.2.1: MC/DC coverage report (100%, ASIL-D)
      │   ├── Solution Sol-1.2.2: SSR review report (I1, no open issues)
      │   └── Solution Sol-1.2.3: Static analysis report (0 mandatory violations)
      │
      └── Goal G1.3:
          'Communication fault cannot cause unintended AEB'
          ├── Solution Sol-1.3.1: E2E protection analysis
          └── Solution Sol-1.3.2: CAN fault injection HIL test (PASS)

  GSN Symbols:
  Rectangle = Goal (G); Parallelogram = Strategy (S); Circle = Solution/Evidence

Safety Case Document Index

Markdownsafety_case_index.md

# Safety Case Document Index — FCAB Item v2.3

## Part 1: Item and Context
- SC-001: Item Definition v1.5 [approved]
- SC-002: Operational Environment Description v1.2 [approved]
- SC-003: Legal and Regulatory Context v1.1 [approved]

## Part 2: Hazard Analysis
- SC-010: HARA Report v2.1 [reviewed I2; approved]
- SC-011: ASIL Justification Document v1.3 [reviewed I2; approved]
- SC-012: Safety Goals and Safe States v2.0 [reviewed I2; approved]

## Part 3: System Safety Concept
- SC-020: Functional Safety Concept v1.8 [reviewed I1; approved]
- SC-021: Technical Safety Requirements v3.2 [reviewed I1; approved]
- SC-022: ASIL Decomposition Evidence v1.1 [reviewed I2; approved]
- SC-023: DFA Report v1.4 [reviewed I2; approved]

## Part 4: Hardware Evidence
- SC-030: Hardware FMEA v2.5 [reviewed I1; approved]
- SC-031: FTA Report v1.3 [reviewed I1; approved]
- SC-032: Hardware Metrics Report (SPFM=99.2%, LFM=91.3%, PMHF=6.8 FIT) [approved]
- SC-033: Fault Injection Test Report v1.2 [reviewed I1; approved]

## Part 5: Software Evidence
- SC-040: SW Safety Requirements v4.1 [reviewed I1; 47 SSRs; 0 open gaps]
- SC-041: SW Architecture Description v2.3 [reviewed I2; approved]
- SC-042: MISRA Compliance Report (0 mandatory violations; 3 deviations) [approved]
- SC-043: Static Analysis Report (Polyspace: 0 red; 2 orange resolved) [approved]
- SC-044: Unit Test Report (100% MC/DC; 247 test cases; 0 failures) [reviewed I1]
- SC-045: Integration Test Report [reviewed I1; approved]

## Part 6: Validation Evidence
- SC-050: Safety Validation Plan v1.2 [approved]
- SC-051: HIL Validation Report [PASS: all SG-01..SG-04 tests passed]
- SC-052: Vehicle Test Report [PASS: 500 km; 0 inadvertent activations]

## Part 7: Assessment
- SC-060: Audit Report #1 (mid-project): 2 major findings; both closed
- SC-061: Audit Report #2 (pre-release): 0 major findings; 3 minor; 2 closed
- SC-062: Functional Safety Assessment: [PENDING — assessor review in progress]

Summary

The safety case is the deliverable that summarises the entire safety argument — it points to all evidence documents and argues why, collectively, they demonstrate that the item is safe. A safety case is not a single document but a structured collection of documents linked by an argument structure (GSN or similar). The assessor evaluates the safety case by reviewing the argument structure for logical completeness (are all hazards addressed?), then spot-checking the evidence (does the FMEA actually cover all safety-relevant failure modes?). A safety case with a complete argument structure but weak evidence (e.g., FMEA with no DC justification) will receive major findings during assessment.

🔬 Deep Dive — Core Concepts Expanded

This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.

Key principles to reinforce:

Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.

🏭 How This Topic Appears in Production Projects

Project integration phase: The concepts covered in this lesson are most commonly encountered during ECU integration testing — when multiple software components from different teams are combined for the first time. Issues that were invisible in unit tests frequently surface at this stage.
Supplier/OEM interface: This is a topic that frequently appears in technical discussions between Tier-1 ECU suppliers and OEM system integrators. Engineers who can speak fluently about these details earn credibility and are often brought into critical design review meetings.
Automotive tool ecosystem: Vector CANoe/CANalyzer, dSPACE tools, and ETAS INCA are the standard tools used to validate and measure the correct behaviour of the systems described in this lesson. Familiarity with these tools alongside the conceptual knowledge dramatically accelerates debugging in real projects.

⚠️ Common Mistakes and How to Avoid Them

Assuming default configuration is correct: Automotive software tools ship with default configurations that are designed to compile and link, not to meet project-specific requirements. Every configuration parameter needs to be consciously set. 'It compiled' is not the same as 'it is correctly configured'.
Skipping documentation of configuration rationale: In a 3-year ECU project with team turnover, undocumented configuration choices become tribal knowledge that disappears when engineers leave. Document why a parameter is set to a specific value, not just what it is set to.
Testing only the happy path: Automotive ECUs must behave correctly under fault conditions, voltage variations, and communication errors. Always test the error handling paths as rigorously as the nominal operation. Many production escapes originate in untested error branches.
Version mismatches between teams: In a multi-team project, the BSW team, SWC team, and system integration team may use different versions of the same ARXML file. Version management of all ARXML files in a shared repository is mandatory, not optional.

📊 Industry Note

Engineers who master both the theoretical concepts and the practical toolchain skills covered in this course are among the most sought-after professionals in the automotive software industry. The combination of AUTOSAR standards knowledge, safety engineering understanding, and hands-on configuration experience commands premium salaries at OEMs and Tier-1 suppliers globally.