Qualitative and Quantitative Risk Assessment
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A Safety Management System (SMS) relies on effective risk assessment as a core function to support the identification and mitigation of hazards that may affect the safe delivery of aviation products or services.
Two principal methodologies are applied within the industry: Qualitative and Quantitative risk assessments. (Both serve vital roles, depending on the nature of the hazard, available data, and regulatory or operational context.)
Qualitative Risk Assessment offers the potential of agility, simplicity, and wide applicability across all levels of the organisation, while Quantitative Risk Assessment delivers a more measured, data-driven depth.
Mature SMSs develop internal capability for both Quantitative & Qualitative approaches, applying each in appropriate contexts with consistency and visibility.
Organisations need to remain vigilant against complacency, recognising that the effectiveness of risk assessment is only as good as the competence, data, and decision-making frameworks that support it.
Qualitative Risk Assessment (QRA)
A qualitative assessment involves subjective judgment to evaluate the severity and likelihood of potential consequences, typically using categorical scales such as:
• Severity: Catastrophic / Major / Minor / Negligible
• Likelihood: Frequent / Occasional / Remote / Extremely Remote
These assessments often result in a risk matrix rating (e.g., high, medium, low).
Qualitative risk assessments present several challenges, including subjectivity and bias, as results may vary significantly between assessors. In the absence of structured guidance, the application of risk ratings can become inconsistent and open to misinterpretation.
Furthermore, this approach may lack the necessary granularity for high-stakes, data-driven decision-making and often oversimplifies complex risk scenarios, potentially leading to ineffective or inadequate safety mitigations.
Quantitative risk assessment poses several challenges, particularly related to data and resource demands. Accurate and sufficient data is not always available, which can compromise the integrity of the analysis.
The process often requires specialised technical expertise and advanced analytical tools, increasing both complexity and associated costs. Additionally, there is a risk of false precision, where results may appear reliable despite being based on weak inputs or flawed assumptions. Due to these factors, quantitative methods are not always well-suited for front-line operational risk management, where simplicity, speed, and practicality are often essential.
Application in Aviation SMS:
• Used when data is limited or hazards are not easily measurable.
• Effective for initial risk screening, risk prioritisation, and incident classification.
• Common in line maintenance, flight operations, ground handling, and safety reporting systems.
Qualitative Risk Assessment Best Practices Include
• Standardise terminology and matrix scales across the organisation.
• Involve multidisciplinary safety teams to mitigate subjectivity.
• Calibrate matrices with historical data and operational feedback.
• Document justifications and reasoning clearly for audit and review purposes.
Quantitative Risk Assessment (QRA)
Quantitative assessments use numerical methods to estimate risk, involving probabilistic modelling, historical data, and statistical techniques to assign numeric values to:
• Probability of occurrence
• Expected severity of outcome
• Risk exposure (e.g., fatalities per flight hour)
Often expressed in terms such as:
• Risk = Frequency × Consequence
• Risk per flight hour / per operation / per aircraft
QRA Application in Aviation SMS:
• Used for high-complexity or high-criticality systems, such as:
>> Aircraft system design (e.g., FHA, PSSA, SSA under ARP 4761)
>> Airspace risk modelling
>> Runway incursion/collision probability
• Often required in certification, airworthiness, or design environments.
QRA Best Practices:
• Use validated data sources (e.g., Flight Data Monitoring, MOR databases).
• Apply Monte Carlo simulation, fault tree analysis (FTA), or Bayesian networks for system risk modelling.
• Align with industry benchmarks (e.g., 1 × 10⁻⁹ fatal accident rate per flight hour for catastrophic failure conditions).
• Incorporate uncertainty margins and confidence levels in assessments.
Combining Qualitative and Quantitative
Using qualitative screening tools to prioritise risks and applying quantitative methods for deep-dive analysis of high-priority hazards.
Example:
• Use a qualitative matrix for general safety reports.
• Escalate to quantitative fault tree analysis for potential failure modes in aircraft braking systems or flight control anomalies.
Next Steps
Sofema Aviation Services is committed to supporting aviation organisations in their journey towards comprehensive risk management excellence, providing professional training and guidance tailored to the unique needs of each organisation.
For more information, please email team@sassofia.com or visit our websites:
