The Failure Condition work item type represents ARP 4761 safety assessment outcomes—the adverse conditions that systems must be designed to prevent or mitigate.
A failure condition describes what can go wrong at the system or subsystem level, its severity classification per aerospace standards, the flight phase(s) in which it can occur, allocated design assurance levels (DAL), and probability targets. Unlike failure modes (which describe component-level “how it fails”), failure conditions answer “what failure states must be managed?”
Failure conditions serve as the primary work item in four interconnected risksheet templates:
FHA (Functional Hazard Assessment): Initial identification of failure conditions with severity classification and DAL allocation
PSSA (Preliminary System Safety Assessment): Allocation of safety objectives and probability targets to failure conditions
SSA (System Safety Assessment): Final verification and evidence collection against those safety objectives
FTA (Fault Tree Analysis): Hierarchical decomposition of failure conditions using AND/OR gate logic
The work item type failureCondition unifies these four analysis contexts through reusable custom fields. Each risksheet template uses a subset of these fields appropriate to its stage in the V-model.
ARP 4761 severity classification: Catastrophic (cat), Hazardous (haz), Major (maj), Minor (min), No Safety Effect (nse). Drives DAL allocation in FHA risksheet.
flightPhase
Enum: failureCondition-phase
required
Flight phase(s) in which failure condition can occur: ground operations, takeoff, climb, cruise, descent, approach, landing. Multiple phases may apply.
safetyObjective
String (free text)
—
Free-form safety objective statement allocated to this failure condition during PSSA. Example: “System shall prevent uncommanded roll during cruise flight.”
probabilityTarget
Enum: safetyObjective-probability
—
Probability/quantitative target for this failure condition per PSSA allocation: Catastrophic (< 1×10⁻⁹/hour), Hazardous (< 1×10⁻⁷/hour), Major (< 1×10⁻⁵/hour), Minor (< 10⁻³/hour). See application for exact scale values.
dalAllocation
Enum: dal
—
Design Assurance Level (DAL) allocated to this failure condition during FHA: A (catastrophic risk), B (hazardous risk), C (major risk), D (minor risk), E (no safety effect). Maps from classification in FHA.
effectDescription
Text (plain)
—
Detailed description of the failure condition’s effect on aircraft and occupants. Used in FHA and PSSA for context and traceability documentation.
verificationStatus
Enum: status
—
Evidence verification state during SSA: Draft, In Review, Approved, Published. Tracks whether safety objective has sufficient evidence (test results, analysis, inspection records).
gateType
Enum: fta-gateType
—
Fault tree gate logic (used in FTA only): AND (all inputs required), OR (any input sufficient), Inhibit (conditional), K-of-N (k-out-of-n voting). Defines how lower-level failure events combine to produce this failure condition.
classification and probabilityTarget propagate down the tree
The exact enumeration values for safetyObjective-probability and fta-gateType should be verified in your Polarion project’s enum definitions. Some gates (e.g., K-of-N) may be project-specific extensions.
Failure condition classification directly maps to Design Assurance Level (DAL) under ARP 4761:
Copy
Ask AI
Catastrophic (cat) → DAL A│ No hazard mitigations acceptable. Catastrophic failure with no safety barrier.│ Probability Target: < 1×10⁻⁹ per flight hour│ Example: Total loss of primary flight control surfaceHazardous (haz) → DAL B│ Severe but controllable. Single-point failure or reduced safety margins.│ Probability Target: < 1×10⁻⁷ per flight hour│ Example: Loss of secondary flight control with reversion to manualMajor (maj) → DAL C│ Significant degradation in aircraft safety with crew compensation.│ Probability Target: < 1×10⁻⁵ per flight hour│ Example: Loss of flight director or autopilotMinor (min) → DAL D│ Minor impact on safety. Crew easily manages with normal procedures.│ Probability Target: < 10⁻³ per flight hour│ Example: Incorrect flight plan load or minor display anomalyNo Safety Effect (nse) → DAL E│ Inoperative condition with no safety impact.│ No probability target. No safety requirement.│ Example: Loss of landing light or non-essential display feature
Insert a new row in the FHA risksheet (Risks/FCC System FHA document)
Enter failure condition title (what goes wrong): e.g., “Uncommanded pitch control input”
Select classification from dropdown: Catastrophic, Hazardous, Major, Minor, or No Safety Effect
Select flight phase or multiple phases where hazard is relevant
Enter effect description (what happens to aircraft and crew): e.g., “Aircraft pitches nose-down uncontrollably during cruise, potential loss of control”
DAL allocation auto-calculates or is manually set based on classification
Failure conditions can have parent-child relationships for decomposition:In FTA, this hierarchy is mandatory: each failure condition is decomposed into lower-level events (intermediate or basic) via AND/OR gate logic. The gateType field determines how child events combine:
AND gate: All child events must occur to trigger parent failure condition
OR gate: Any one child event triggers parent failure condition
Inhibit gate: Child event triggers parent only under specified condition
K-of-N gate: K out of N child events must occur (voting logic)
Use AND gates for fault tolerance analysis (redundancy check). Use OR gates for path independence analysis (single-point failure). Document gate selection rationale in effect description.
Aircraft pitches nose-down uncontrollably; potential structural damage; loss of control
B
PSSA Phase (Allocation):
ID
Failure Condition
Safety Objective
Probability Target
DAL
FC-001
Uncommanded pitch control
System shall not provide uncommanded pitch control inputs exceeding ±2° per second
< 1×10⁻⁷/hour
B
Linked Safety Requirement: SR-FCC-022: “Flight control processor shall validate pitch command against stored pilot input within 50 ms”SSA Phase (Verification):
