MSG-3 Analysis (Part V): Aircraft Health Monitoring (AHM)

The latest MSG-3 Revision 2022.1 added a method to integrate AHM capability within the MSG-3 process by introducing new language and decision tree logic (Systems/Powerplant Analysis Level 3) (IP180) and clarified that references to and use of Aircraft Health Monitoring (AHM) require the certification of associated on-aircraft system features (IP 197).

Aircraft Health Monitoring (AHM) integration represents a significant leap towards more efficient and predictive maintenance practices. This approach provides operators with the flexibility to decide whether to adopt the optional use of AHM capabilities for scheduled maintenance. By establishing a clear framework for its application, this process ensures that AHM data can enhance the maintenance program without replacing the traditional MSG-3 structure.

Note: If AHM is applied into the MSG-3 process, Type Certificate Holders (TCHs) must address all elements in the Policy and Procedures Handbook (PPH). To understand how this integrates into the MRB process, refer to our previous article.

Overview of AHM Integration

The revised standard outlines the conditions under which AHM data can be used in MSG-3 analysis. It allows operators to decide whether to incorporate AHM capabilities into their existing maintenance schedules, depending on the specific requirements of their fleet and the qualifications of the system. However, the application of AHM data in MSG-3 depends on the system’s certification and the following key criteria:

1. Installation (qualification of the “on-board” and the “on-ground” segments, both in terms of hardware and software).

2. Qualification of the monitored parameters and thresholds to be representative of the directly or indirectly observed states and performance as a monitoring of system for degradation.

3. Qualification of off-aircraft (ground based) hardware and software utilized in monitoring.

4. Qualification of the Instructions for Continued Airworthiness of the AHMS itself.

5. Controlled service introduction validation.

The use of AHM is limited to non-safety tasks provided the tasks are not covering Candidate Certification Maintenance Requirements (CCMRs).

Incorporating AHM in MSG-3 Analysis

The integration of AHM into the MSG-3 process involves introducing new decision logic, particularly at Level 3, to allow for the assessment and use of AHM data in maintenance planning. This process adds a third layer of analysis, empowering Working Groups (WGs) to determine whether AHM data can define a repetitive maintenance task or offer an alternative process.

IP 180: Systems/Powerplant MSG-3 Logic Diagram – Level 3 Analysis

A new concept, the “AHM candidate”, is introduced in this framework. This is the initial step to assess the applicability and effectiveness of AHM for particular failure causes. If a system’s failure cause falls under AHM’s capabilities, it will be evaluated for its relevance to maintenance tasks. The outcome will be published in the Maintenance Review Board Report (MRBR), where tasks involving AHM will be clearly identified and tracked.

The Three Levels of Decision Logic

Level 1 and Level 2:

The first two levels of the decision logic follow the traditional MSG-3 framework, assessing whether a classic maintenance task is necessary based on operational and safety needs.

Level 3:

Level 3 introduces AHM as an optional tool in the MSG-3 process. This level focuses on leveraging AHM data for more precise maintenance actions, enabling the following:

• Lubrication and Servicing: Determining if these tasks are required based on AHM data.

• Degradation Detection: Identifying signs of system degradation that may necessitate maintenance.

• Hidden Failure Detection (for FEC 8 and 9 only): Detecting failures not easily observable, particularly for complex components.

Each failure cause identified as an AHM candidate will go through a structured analysis to determine if AHM can replace or supplement classic maintenance tasks. The analysis considers:

1. Applicability: Is AHM applicable to the specific failure cause?

2. Time Margin: What is the time between the AHM notification and required actions?

3. Effectiveness: How effective is AHM in addressing the failure cause?

4. Alternative Tasks: Can AHM serve as an alternative to or hybrid with traditional tasks?

Outcomes of Level 3 Analysis:

• No AHM: No AHM capability is suitable for the failure cause.

• AHM Alternatives: AHM can replace classic tasks with alternate procedures.

• AHM Hybrid: A combination of AHM and classic tasks can be used for effective maintenance.

Maintenance Task Flexibility

If AHM alternatives or hybrids are proposed, operators have the flexibility to choose between classic tasks, AHM alternatives, or a hybrid approach. Each option—classic tasks, AHM alternatives, and AHM hybrids—will meet the minimum requirements for the maintenance program. This ensures that operators are not locked into one approach and can adjust as necessary during the aircraft’s service life.

The TCH should also provide procedures which allow switching between the classic tasks and AHM procedures throughout the service life of the aircraft.

Furthermore, manufacturers must ensure that Instructions for Continued Airworthiness are included, outlining how operators can assess the health of the system off-aircraft, including steps to take when monitoring data is unavailable. This ensures continuity of safe operations throughout the aircraft’s life.

AHM Implementation and Certification

For AHM to be used within the MSG-3 process, the associated on-aircraft systems must be certified by the Regulatory Authority. The certification confirms that the system meets all required standards and can safely contribute to maintenance decision-making without compromising safety.

Remember that AHM capabilities are restricted to non-safety tasks and cannot be used for Candidate Certification Maintenance Requirements (CCMRs). This ensures that safety remains the highest priority, and AHM is used only where it has been proven to add value.

Conclusion

The integration of AHM into MSG-3 marks an important evolution in aircraft maintenance practices, offering operators a more flexible, data-driven approach. By introducing the concept of an "AHM candidate" and new decision logic, this framework allows for the application of AHM data to enhance or replace classic maintenance tasks. This methodology empowers operators to use AHM in a way that improves efficiency, reduces costs, and enhances aircraft safety, all while maintaining the integrity of the established MSG-3 process.

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