Common Cause Analysis as Part of the Aircraft Certification Process

Sofema Online (SOL) www.sofemaonline.com considers the key aspects of the CCA process

Common Cause Analysis

Common Cause Analysis (CCA) describes the method used to identify the potential for common-cause failures (CCFs) within a system, where multiple components fail simultaneously due to a single event or shared cause.

In the context of certification, a comprehensive CCA is crucial. Regulatory bodies require a systematic approach to identifying and mitigating safety risks, including CCFs. Therefore, demonstrating a rigorous CCA is often a requirement for certification of an aviation flight control system

In an aircraft flight control system, this could be due to design faults, human errors, or external events that could impact multiple components at once.

• The results of a CCA are often used to inform design changes, preventive measures, or redundancy measures to mitigate the risk of CCFs.
• For example, in a flight control system, a power supply issue might simultaneously affect multiple subsystems.
• By identifying and mitigating these common-cause failures, the overall reliability of the system can be improved.

A multidisciplinary team usually carries out CCA involving system engineers, reliability engineers, safety engineers, and often software and hardware engineers.

Common Cause Analysis Timeline

• The CCA should be initiated during the conceptual design stage and continually updated throughout the lifecycle of the system until its decommissioning.
• This ongoing process should align with the main design reviews, and it must accommodate any design changes or system modifications.

Common Cause Analysis Significant Challenges

• Identification of CCFs can be a complex process due to the high interdependency of modern aircraft systems.
• Challenging to balance the costs and benefits of implementing redundancies or changes to mitigate CCFs.
• Requires a significant time and resource for a comprehensive CCA

Conducting a CCA

• Use of proven CCA methodologies such as Failure Modes and Effects Analysis (FMEA), Fault Tree Analysis (FTA), or Event Tree Analysis (ETA).
• Conduct a thorough and systemic CCA at each major design phase and update it as the design matures.

>> Ensure adequate diversity and redundancy in the system design to mitigate CCFs.

>> Regularly review and update the CCA as the system evolves and as more data becomes available about system reliability and failure modes.

Initiate the Common Cause Analysis (CCA) – 1 to 2 Weeks

• Define the system or process that will be the subject of the analysis.

>> This should include understanding the various components of the system and how they interact.

• Assemble the team which could include system engineers, operations staff, maintenance personnel, etc.

Gather Data – 1 to 2 Weeks

• Investigate the system or process to identify any failures that could potentially be caused by a common cause.

>> This could involve reviewing previous failure data, conducting interviews with staff, and observing the system or process in operation.

Analyze Data – 1 to 2 Weeks

• Analyze the identified potential common cause failures:

>> Use appropriate statistical techniques to determine the likelihood of each identified potential common cause failure.

>> This might involve looking for trends or patterns in the data, using techniques such as root cause analysis or fault tree analysis.

Identify Mitigation Strategies – 1 to 2 Weeks

• For each identified potential common cause failure, identify potential strategies to mitigate the risk of that failure occurring.

>> This could involve changes to the system or process, enhanced monitoring, additional training for staff, etc.

Develop and Implement Action Plan – Several Weeks

• Develop a detailed action plan for implementing the identified mitigation strategies.

>> This plan should include specific actions, responsibilities, timelines, and required resources.

• Carry out the actions identified in the action plan.

>> This could involve making changes to the system or process, providing additional training to staff, implementing new monitoring procedures, etc.

Review and Monitor – Continuous As Required

• Once the mitigation strategies have been implemented, it's important to monitor their effectiveness.

>> This could involve gathering and analyzing data to determine whether the likelihood of the identified potential common cause failures has been reduced.

• Regularly review and update the CCA to ensure it remains accurate and relevant.

>> This should involve repeating the above steps at regular intervals, for example, annually, or when significant changes are made to the system or process.

Next Steps

Sofema Aviation Services offers training to cover Type Certification System Safety Assessment – 5 Days 

For additional questions or comments – please email team@sassofia.com