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Overview

The Aerospace Safety Solution implements the standard ARP 4761 five-level classification scheme. Each classification level is:
  • Assigned to failure conditions during FHA analysis
  • Used to allocate Design Assurance Levels (DAL) automatically via a built-in formula
  • Color-coded for visual emphasis in risksheets and dashboards
  • Linked to probability targets for quantitative safety objectives
The classification is a required field on every failure condition work item and drives downstream traceability to safety requirements, verification activities, and certification objectives.

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Classification Levels

ClassificationIDDescriptionARP 4761 DefinitionDAL AllocationColor
CatastrophiccatLoss of essential function, flight crew unable to cope, multiple fatalities probableFailure condition would prevent safe operation or result in loss of aircraft/multiple fatalitiesDAL ARed
HazardoushazSignificant degradation of safety margins, flight crew effort required, serious injury possibleFailure condition would reduce safety margins and require flight crew action to avoid serious injury or fatalityDAL BOrange
MajormajReduced safety margins, crew alert required, passenger discomfortFailure condition would reduce safety margins and require crew awareness but safe flight possibleDAL CYellow
MinorminMinor operational impact, passenger inconvenienceFailure condition causes minor inconvenience or discomfort but has no direct effect on safetyDAL DBlue
No Safety EffectnseNo impact on safety, maintenance issue onlyFailure condition has no impact on safetyDAL EGrey

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Classification-to-DAL Mapping Formula

The FHA risksheet includes an automatic formula that derives the Design Assurance Level from the failure condition classification. This implements the standard ARP 4761 allocation rule: diagram The formula is embedded in the DAL column of the FHA risksheet and recalculates whenever the classification changes. You do not manually enter the DAL level—it is derived from your classification assignment.
Once the DAL is allocated to a failure condition, it flows down to all linked safety requirements (safetyRequirement items). This ensures that requirements addressing catastrophic failures receive the most rigorous development and verification treatment.

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Color Coding Convention

The Aerospace Safety Solution uses consistent color coding across all safety analysis risksheets (FHA, SFMEA, DFMEA, FTA, CCA): diagram These colors appear in:
  • Row headers — the leftmost column of each risksheet row
  • Classification cells — the severity value itself
  • DAL cells — the corresponding allocation level
  • Dashboard reports — visual risk matrices and trend charts
Color coding enables rapid visual scanning to identify high-severity items during reviews and status meetings.

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Flight Phase Context

Classification severity may vary by flight phase. A failure during cruise may be classified as Hazardous, while the same failure during landing might be Catastrophic. The failure condition record includes a Flight Phase field to capture this context:
PhaseDefinitionNotes
GroundPre-flight, taxi, parkingLower consequence window
TakeoffRotation and initial climbCritical phase; high consequence potential
ClimbAfter initial climb to cruise altitudeLonger recovery time; moderate consequence
CruiseSustained level flightLongest duration; crew may have time to mitigate
DescentDescent to approach altitudeDecreasing altitude reduces recovery options
ApproachInstrument or visual approachApproach procedures constrain options
LandingFlare, touchdown, rolloutLowest altitude; highest consequence potential
Confirm whether your project uses all seven flight phases or a reduced set. Some projects consolidate phases or use only the most critical phases (Takeoff, Cruise, Landing).

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Safety Objective Probability Targets

Each failure condition classification level is associated with a probability target—a quantitative safety objective that the design must achieve through architecture and risk controls:
ClassificationProbability TargetThreshold
CatastrophicExtremely Improbable< 10⁻⁹ per flight hour
HazardousExtremely Remote< 10⁻⁷ per flight hour
MajorRemote< 10⁻⁵ per flight hour
MinorReasonably ProbableNo specific numerical target
No Safety EffectProbableNo safety requirement
The probability target is not the observed failure rate—it is the required level of safety that your design and verification activities must demonstrate. During PSSA (Preliminary System Safety Assessment), you allocate this probability target to individual system functions and safety requirements.

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Role in Safety Assessment Cascade

Failure condition classification is the linchpin connecting three major safety analysis activities: diagram

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Integration with Work Item Types

Classification is a custom field on the failureCondition work item type. Related work item types reference or inherit this classification:
Work Item TypeUsageNotes
failureConditionSource of truthStores the classification value directly
safetyRequirementInheritanceInherits DAL from allocated failure condition(s)
systemElementCategorizationMay be classified separately (SC/CC); different scope than failure classification
functionAnalysis contextFunctions link to failure conditions; classification flows from condition to requirement
riskControlMitigation scopeRisk controls are scoped by DAL to address appropriate severity levels

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Risksheet Views and Filtering

The FHA risksheet includes built-in views and filters for working with classifications:

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Full Analysis View

Displays all columns: Function, Failure Condition, Flight Phase, Effect Description, Classification, Probability Target, DAL, Safety Requirements, Verification Status. Rows are sorted by classification severity (Catastrophic first).

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Classification Summary View

Focuses on severity and risk allocation: Function, Failure Condition, Classification, DAL, Safety Requirement Count. Filtered to show only Hazardous and above (excludes Major, Minor, No Safety Effect).

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Safety Objectives View

Emphasizes probability targets and requirements: Failure Condition, Classification, Probability Target, DAL, Safety Requirement ID, Safety Requirement Title. Used during PSSA to set quantitative objectives.

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Traceability View

Full chain: Function, Failure Condition, Classification, Safety Requirement ID/Title, Verification Status. Used to confirm that every high-severity failure condition has a corresponding requirement and verification activity.

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Classification Consistency Rules

The Aerospace Safety Solution enforces several consistency checks on failure condition classification:
Every failure condition must have a classification assigned. The field is mandatory. A failure condition cannot be saved without selecting a classification level.
The classification must reflect the actual safety consequence described in the failure condition. A reviewer should be able to read the effect description and agree that the chosen classification is justified. Vague or over-stated classifications may be flagged during formal review.
Confirm whether the Classification Consistency Report automatically checks for orphaned failure conditions (those without classification) or mis-matched classifications (where the effect description does not support the chosen severity).

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Relationship to Other Enumerations

Failure condition classification is distinct from but related to:
EnumerationScopeRelationship
Failure Condition Phase (flight phase)When the failure occursClassification severity may depend on flight phase
DAL Levels (A–E)Design rigor levelDirectly derived from classification via formula
Failure Mode Severity (FMEA)Individual failure mode severityDifferent scale; FMEA severity rolls up to failure condition classification
Risk Control TypeHow mitigation is implementedRisk control scope is determined by the DAL of the failure condition it addresses
Safety Assurance Level (SAL)Security requirementsSeparate enumeration for DO-326A security threats; not related to safety classification

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Example: Assigning Failure Condition Classification

Scenario: During FHA of the Flight Control System, you identify the failure condition “Loss of Primary Flight Control Authority.”
  1. Analyze impact: Flight crew cannot control pitch, roll, or yaw. Aircraft is uncontrollable. Multiple fatalities probable.
  2. Assign classification: Based on impact analysis, this is Catastrophic.
  3. Observe DAL: The FHA risksheet automatically allocates DAL A.
  4. Set probability target: DAL A implies Extremely Improbable (< 10⁻⁹ per flight hour).
  5. Define safety requirements: During PSSA, allocate safety requirements that achieve this probability target (e.g., redundant flight control channels, automatic switchover logic, health monitoring).
If later you discover that flight crew can recover control via secondary actuators with high probability, you may downgrade the classification to Hazardous, which automatically downgrades the DAL to B and reduces the probability target to Extremely Remote (< 10⁻⁷).
Record the rationale for your classification choice in the failure condition’s effect description or in a linked comment. During formal review, this helps the team understand your risk assessment and agree on the severity level.

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See Also

Code: .polarion/tracker/fields/failureCondition-custom-fields.xml (0.67) · .polarion/nextedy/models/rtm.yaml (0.61) · modules/RiskTemplates/FHATemplate/attachments/risksheet.json (0.59) · .polarion/tracker/fields/failureCondition-classification-enum.xml (0.58) · modules/RiskTemplates/SSATemplate/attachments/risksheet.json (0.58) · .polarion/tracker/fields/failureMode-custom-fields.xml (0.55) · .polarion/nextedy/sheet-configurations/DO-160G Environmental Qualification.yaml, Component RTM.yaml, Configuration Index.yaml, Design Verification Sheet.yaml, Interface Control Matrix.yaml, Problem Report Tracker.yaml, Process Steps.yaml, Review Action Item Tracker.yaml, SOI Stage Gate Dashboard.yaml, Use Steps Specification.yaml, User Need Validation Sheet.yaml, characteristics.yaml, component-characteristics.yaml, customer-requirements.yaml, design-requirements.yaml, subsystem-functions.yaml, subsystem-verification.yaml, system-elements.yaml, test-verification.yaml (0.54) · .polarion/tracker/fields/hazard-hazardCategory-enum.xml, hazard-operationalPhase-enum.xml, hazard-acceptanceAuthority-enum.xml (0.54) · .polarion/tracker/fields/safetyObjective-probability-enum.xml (0.54) · modules/RiskTemplates/FTATemplate/attachments/risksheet.json (0.52)