Means Of Compliance

Means of Compliance (systems-engineering-safety/certification/means-of-compliance)

Use when the task is selecting the acceptable means of compliance for each certification item of a civil aircraft program and building the per-item compliance matrix: which of the six MOC classes (MOC 1 engineering/analysis, MOC 2 ground test, MOC 3 flight test, MOC 4 simulation/analysis tool, MOC 5 certification by similarity, MOC 6 safety assessment) shows compliance with an applicable regulation paragraph, whether the chosen method is acceptable for the item kind, failure severity and development assurance level, and whether the matrix covers every certification item.

This leaf owns the per-certification-item MOC matrix and the coverage method. It pairs with certification-basis (the leaf that determines the applicable paragraphs this leaf assigns MOC for) and with the program-level certification sequencing leaves. It does NOT determine the certification basis and does NOT scope ARP4754A verification method assignment.

Domain quick reference

• The MOC six-class scheme, summarized at reference level from public certification guidance (EASA and FAA style MOC categories): MOC 1 engineering/analysis, MOC 2 ground test, MOC 3 flight test, MOC 4 simulation/analysis tool, MOC 5 certification by similarity, MOC 6 safety assessment.
• Suitability by item kind (deterministic summary, ordered primary first):
  • structure: MOC 1 analysis primary with MOC 2 static/ground test evidence; a novel structural item adds flight test MOC 3.
  • systems (electronic): MOC 1 plus MOC 6 for catastrophic or hazardous failures; MOC 4 simulation is acceptable for DAL C-E.
  • powerplant: MOC 2 bench/ground test and MOC 3 flight test typical, MOC 1 analysis supporting.
  • equipment: MOC 2 environmental qualification test (DO-160 style) with MOC 1 analysis support.
  • software: MOC 1 lifecycle data per DO-178C plus MOC 4 tool qualification where tools are used; the software MOC is the DO-178C process assurance, not a test article.
  • hardware: MOC 1 plus MOC 2 (DO-254 style verification).
  • performance and handling: MOC 3 flight test with MOC 1 analysis and MOC 4 simulation.
• Acceptance rules: a catastrophic systems item requires MOC 6 in its compliance set; a novel structure or systems item requires a test MOC (2 or 3) in addition to analysis; MOC 5 similarity is rejected for any novel item (similarity is reserved for minor changes and is never auto-recommended by this leaf).
• Coverage: overall score = (items with at least one accepted MOC) / (all items); per-kind scores reported alongside.
• Readiness verdict: PASS when coverage is 1.0 and no catastrophic systems item lacks MOC 6, otherwise FAIL with the item-level reasons.

Workflow

1. Enumerate the certification items: for each applicable regulation paragraph record item_id, regulation_paragraph, item_kind (one of structure, systems, powerplant, equipment, software, hardware, performance, handling), failure_severity, development_assurance_level and the novelty screen flag.
2. Recommend the MOC set per item with moc_suitability(item_kind, severity, dal, novel); the function returns the ordered list with the primary MOC first, or raises ValueError on an unknown kind, severity or DAL string.
3. Gate each assigned set with accept_item(item, recommended): confirm the MOC 6 requirement for catastrophic systems items, the test MOC requirement for novel structure or systems items, and the MOC 5 rejection for novel items. Pass item["assigned_mocs"] to evaluate a team-proposed set against the suitability recommendation.
4. Assemble the matrix with build_compliance_matrix(items): one row per certification item with recommended MOCs, the MOC set under evaluation, the primary MOC, the acceptance result and reason, plus the collected issues list.
5. Score coverage with coverage_score(matrix): overall ratio of items with at least one accepted MOC, and the per-kind ratios.
6. Close with compliance_verdict(matrix): PASS only when coverage is 1.0 and every catastrophic systems item carries MOC 6; the reasons list names every rejected item.
7. Confirm the deterministic checks with the contract test scripts/test_means_of_compliance.py.

Worked example

Three certification items from a transport category program:

1. FCS-1 (25.671, systems, catastrophic, DAL A, novel true): the fly-by-wire flight control system.
2. STR-1 (25.307, structure, hazardous, novel false): primary structure static strength.
3. PP-1 (25.901, powerplant, major, novel false): powerplant installation.

• FCS-1 recommendation: moc_suitability("systems", "catastrophic", "A", True) returns [1, 6, 2]: analysis primary, the MOC 6 safety assessment mandated by the catastrophic severity, and ground test MOC 2 from the novelty screen, so a test MOC is present.
• STR-1 recommendation: moc_suitability("structure", "hazardous", "n/a", False) returns [1, 2]: MOC 1 analysis primary with static test evidence; hazardous severity on a structural item does not trigger any MOC 6 requirement.
• PP-1 recommendation: moc_suitability("powerplant", "major", "n/a", False) returns [2, 3, 1]: bench/ground test and flight test with supporting analysis.
• Matrix: all three rows accepted, zero issues, primary MOCs 1, 1, 2; coverage_score returns overall 1.0 and 1.0 for each of systems, structure and powerplant; compliance_verdict returns PASS.
• Negative check: assigning FCS-1 only MOCs 1 and 4 makes accept_item return False with the MOC 6 reason, and compliance_verdict returns FAIL for the matrix: the catastrophic flight control system must carry the safety assessment MOC 6.

Verification

• Confirm the three worked example recommendations: FCS-1 [1, 6, 2] with MOC 6 and a test MOC present, STR-1 [1, 2] with MOC 1 primary and no MOC 6, PP-1 [2, 3, 1].
• Confirm compliance_verdict PASS for the full three item matrix and FAIL with the MOC 6 reason when FCS-1 is assigned only MOCs 1 and 4.
• Confirm coverage_score returns overall 1.0 for the full set and 0.5 with per-kind ratios when one of two items is rejected.
• Confirm ValueError rejection of item_kind "quantum", severity "very-bad", unknown DAL strings, and an empty item list.
• Run the contract test offline: python3 scripts/test_means_of_compliance.py (34 tests, deterministic).

Related leaves

• systems-engineering-safety/certification/certification-basis: names the applicable regulation paragraphs this leaf assigns MOC for.
• avionics/far-cs25/airworthiness (program-level): the coarse four-way analysis/test/inspection/similarity selection and program sequencing around this per-item matrix.
• avionics/far-cs25/special-conditions: the special condition scope for the novel features screened by the novelty flag.
• systems-engineering-safety/arp4754a/verification-planning: ARP4754A verification method assignment, the development activity this leaf does not cover.

Pitfalls

• Releasing a catastrophic systems item without MOC 6: the safety assessment is mandated for catastrophic (and hazardous) systems failures, so FCS-1 assigned only MOCs 1 and 4 is rejected with the MOC 6 reason and the compliance verdict FAILs even if other items pass.
• Accepting similarity for a novel item: MOC 5 is rejected for any novel item - similarity is reserved for minor changes and is never auto-recommended - and a novel structure or systems item needs a test MOC (2 or 3) in addition to analysis.
• Using simulation where it is not allowed: MOC 4 simulation is acceptable for systems items at DAL C-E, so it neither substitutes for the test MOC of a novel item nor for the MOC 6 of a catastrophic one.
• Reading the overall score without the verdict gates: coverage 1.0 alone is not readiness - PASS requires coverage 1.0 AND every catastrophic systems item carrying MOC 6, with the reasons list naming each rejected item.
• Recommending a MOC set out of the suitability order: the function returns the ordered list with the primary MOC first (FCS-1 [1, 6, 2], STR-1 [1, 2], PP-1 [2, 3, 1]), and unknown kinds, severities or DAL strings raise ValueError instead of scoring.
• Confusing this matrix with neighboring scopes: this leaf assigns per-item MOC but does not determine the certification basis (certification-basis owns that) and does not scope ARP4754A verification method assignment (verification-planning owns that).

Behavior contract (gate 3)

Run the deterministic contract test (stdlib unittest, offline):

python3 scripts/test_means_of_compliance.py

The test covers suitability per item kind (structure, systems, powerplant, equipment, software, hardware, performance, handling), the MOC 6 severity gating and DAL C-E MOC 4 allowance for systems items, novelty upgrades and MOC 5 rejection, acceptance gating, matrix construction with the worked example items FCS-1, STR-1 and PP-1, coverage math overall and per kind, PASS and FAIL verdict logic with the MOC 6 reason, and ValueError rejection of unknown kinds, severities, DALs and an empty item list.

Compliance

• FAR-25 and CS-25 are cited as reference only: regulation paragraph numbers such as 25.671, 25.307 and 25.901 identify the certification items in the worked example. The MOC six-class scheme and the suitability table are deterministic summaries at reference level derived from public certification guidance; no verbatim AMC or regulatory text is reproduced and no standard is reproduced.
• compliance: STANDARDS-REF, gated: false.