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Detection Scale Overview

The detection scale measures how well existing or proposed detection mechanisms can identify a failure mode. Unlike typical automotive FMEA scales where 1 represents the best detection and 10 represents the worst, the Aerospace Safety Solution uses a 6-point scale where 1 represents the best detection capability and 5 represents undetectable failures. A Detection value of 0 indicates the analysis is incomplete. diagram

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Detection Enumeration Values

Detection LevelIDNameDescriptionAerospace Context
00UnanalyzedAnalysis incomplete; detection capability not yet assessedDefault value; analysis in progress
11Very High / BITE / AutomatedContinuous automated monitoring or hardware watchdog; extremely high likelihood of detection before hazardous condition developsBuilt-In Test Equipment (BITE), redundant sensor voting, automated shutdown systems
22High / Periodic TestGround-based diagnostic test or scheduled maintenance inspection; high likelihood of detection between flightsMaintenance checks, flight-line testing, health monitoring during scheduled servicing
33Moderate / Crew AlertCaution/warning system or crew annunciation; moderate likelihood of detection during normal operationCockpit alerts, caution/warning lights, EICAS messages, crew notification systems
44Low / Operational ObservationAnomalous behavior detectable during normal operation, but no explicit alerting mechanism; requires crew or operational personnel awarenessDegraded performance, unusual system behavior observed operationally without automated alert
55Very Low / UndetectableLatent failure with no BITE, no inspection method, and no operational observability; detection impossible before hazard manifestsSingle-point failures in dormant systems, failures requiring disassembly to detect

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Detection vs. Occurrence vs. Severity

Detection is one of three inputs to the Risk Priority Number (RPN) formula used in FMEA analysis: \text{RPN} = \text{Severity} \times \text{Occurrence} \times \text{Detection}
MetricPurposeScaleInterpretation
SeverityHow severe is the failure’s effect?1 (No Effect) to 5 (Catastrophic)Impact on safety, performance, or customer satisfaction
OccurrenceHow likely is the failure to occur?0 (Unanalyzed) to 5 (Frequent)Failure probability per flight hour (1E-9 to >1E-3)
DetectionHow likely is it to be detected?0 (Unanalyzed) to 5 (Undetectable)Effectiveness of detection/monitoring mechanisms
A low Detection value (1–2) indicates effective detection mechanisms, which lowers RPN. A high Detection value (4–5) indicates poor detectability, which increases RPN and typically requires mitigation through improved detection or prevention controls.

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Pre-Mitigation and Post-Mitigation Detection

The Detection enumeration is used in two contexts within failure mode analysis:

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Pre-Mitigation Detection

The premitigationDetection field captures the detection capability of failure modes before mitigation controls are implemented. This represents the baseline risk assessment. 
"premitigationDetection": 4  // Low detection; operational observation only

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Post-Mitigation Detection

The postmitigationDetection field captures the detection capability after risk controls (improvements to detection mechanisms, BITE upgrades, process changes) are implemented. This demonstrates risk reduction effectiveness. 
"postmitigationDetection": 2  // Improved to High; periodic ground testing added
Mitigation strategies that improve detection (e.g., adding BITE, implementing automated monitoring, establishing inspection procedures) lower the post-mitigation Detection value, which directly reduces post-mitigation RPN and demonstrates control effectiveness.

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Custom Field Integration

Detection values are stored in two custom fields on the failureMode work item type:
Field NameField IDTypeDefaultPre/PostDescription
Premitigation DetectionpremitigationDetectionEnumeration (detection)0 (Unanalyzed)PreDetection capability before mitigation controls
Postmitigation DetectionpostmitigationDetectionEnumeration (detection)0 (Unanalyzed)PostDetection capability after mitigation controls
Both fields reference the same enumeration (detection) with the 6 values shown above.

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Detection in FMEA Risksheets

Detection columns appear in both System-level FMEA (SFMEA) and Design FMEA (DFMEA) risksheets: 
# Example: SFMEA Risksheet Column Configuration
- name: "Premitigation Detection"
  fieldId: "premitigationDetection"
  type: "enum"
  level: "risk"
  viewType: "dropdown"
  
- name: "Postmitigation Detection"
  fieldId: "postmitigationDetection"
  type: "enum"
  level: "risk"
  viewType: "dropdown"
Users select detection values from dropdown menus in risksheet cells. The RPN formula automatically recalculates when Detection values change.

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Aerospace-Specific Detection Mechanisms

Unlike automotive FMEA, aerospace detection mechanisms are highly specialized and driven by certification requirements (DO-178C, DO-254, ARP 4761):
Detection MechanismDetection LevelExamplesCertification Basis
BITE (Built-In Test Equipment)1–2Continuous health monitoring, redundant voting logic, automated shutdownDO-254 (HW), DO-178C (SW)
Periodic Maintenance Inspection2Flight-line checks, borescope inspections, functional tests between flightsARP 4161 (Maintenance)
Crew Annunciation3Master caution/warning lights, EICAS messages, flight deck alertsARP 4754A (Safety Assessment)
Operational Observation4Crew detects performance degradation or unusual behavior during normal flight operationsOperational procedures, crew training
Latent/Undetectable5Single-point failures in dormant systems, failures only revealed by accidentHigh-integrity redundancy required
Specific detection mechanisms and their classification within your project may vary based on system architecture and certification strategy. Consult your Safety Assessment (PSSA/SSA) and Failure Mode Analysis documents for project-specific detection strategy.

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RPN Calculation Example

Consider a failure mode in an aircraft fuel system: 
Failure Mode: Fuel filter bypass valve sticks closed
Severity: 4 (Major — loss of fuel flow, engine failure)
Premitigation Occurrence: 3 (Remote — 1E-7 to 1E-5 per flight hour)
Premitigation Detection: 5 (Undetectable — no BITE, latent until engine start)

Premitigation RPN = 4 × 3 × 5 = 60 (HIGH RISK)
Mitigation: Implement automated BITE to detect filter pressure drop before flight. 
Postmitigation Occurrence: 3 (unchanged)
Postmitigation Detection: 1 (Very High — automated BITE monitors filter pressure)

Postmitigation RPN = 4 × 3 × 1 = 12 (ACCEPTABLE)

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Visual Detection Assessment Matrix

diagram

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Grounding and Validation

This page documents the Detection enumeration as defined in the Aerospace Safety Solution codebase. Project-specific detection strategies, mechanism classifications, and RPN thresholds may differ. Consult your project’s:
  • Safety Assessment Plan (SAP) for detection strategy
  • Failure Mode Analysis (FMA) documentation for mechanism details
  • Risk Control documentation for mitigation-driven detection improvements
The Detection enumeration is a critical input to risk prioritization. Accurate assessment of detection capability—supported by design analysis, testing protocols, and verification evidence—is essential for DO-178C/DO-254/ARP 4761 certification compliance.
Code: .polarion/tracker/fields/failureMode-custom-fields.xml (0.57) · .polarion/tracker/fields/failureMode-detection-enum.xml (0.55) · .polarion/nextedy/models/rtm.yaml (0.53) · .polarion/pages/spaces/_default/Requirements Traceability Summary/page.xml, Verification Validation Summary/page.xml, Risk Control Effectiveness Report/page.xml, System Decomposition Report/page.xml, FMEA Coverage Report/page.xml, Classification Consistency Report/page.xml, System FMEA Report/page.xml, System Structure Navigator/page.xml (0.52) · .polarion/pages/scripts/velocity/nextedy_solutions.vm (0.51) · .polarion/nextedy/sheet-configurations/MIL-STD-882E Hazard Tracking Log.yaml (0.49) · modules/RiskTemplates/SubSystem-FMEATemplate/attachments/risksheet.json (0.48) · .polarion/tracker/fields/failureMode-fmOccurrence-enum.xml (0.47) · .polarion/tracker/fields/resolution-enum.xml, .polarion/tracker/fields/changerequest-resolution-enum.xml, .polarion/tracker/fields/changerequest-status-enum.xml, .polarion/tracker/fields/work-record-type-enum.xml, .polarion/tracker/fields/yesno-enum.xml (0.47) · .polarion/nextedy/sheet-configurations/ARP 4761 Safety Assessment Traceability.yaml (0.46)