Tracking Maintenance: Aircraft vs. Component-Level Control

Aircraft Maintenance Tasks can be defined at different levels, depending on whether they apply to the aircraft as a whole or to individual components. While The Aircraft Maintenance Program’s main process, the MRB, primarily defines on-aircraft maintenance tasks (aircraft-level), certain components have strict limitations that require tracking at the part or assembly level.

Life-Limited Parts (LLP), for instance, must be permanently removed once they reach their maximum lifespan, while Time-Controlled Components may require the removal for maintenance to be performed in a workshop to return the component to a specified standard, the replacement of sub-components of the assembly by new ones, or the inspection or test of component’s performance, after a service period controlled at component level.

Properly distinguishing between the need to control maintenance tasks at aircraft-level or component-level tasks ensures that maintenance is performed effectively and that parts remain airworthy throughout their service life.

Maintenance Review Board Report Tasks

The evolution from MSG-2 to MSG-3 methodology in the MRB process marked a shift in decision logic from a component-level, bottom-up failure-effect analysis to a system-level, top-down approach. This change emphasizes maintaining overall system functionality rather than focusing solely on individual component failures, which are monitored by the Reliability Program.

Example: Consider a maintenance task that applies to both engines and is defined at the aircraft level. If no component-level interval tracking is required and one engine is replaced, the task’s interval does not reset—it still counts from the last accomplishment on the aircraft. In contrast, if the MRBR requires component-level tracking, or the operator decides to track individually for reliability reasons, replacing an engine resets the interval for that specific engine only.

The MSG-3 analysis procedure is primarily used to define on-aircraft maintenance tasks. In some instances, it is not practical to do the task on-aircraft. Off-aircraft tasks may be included only if they meet MSG-3’s applicability and effectiveness criteria.

MSG-3 is not intended to define all shop-type tasks for components, although in some cases, the only task that satisfies the criteria may be off-aircraft. For such tasks, the task description must clearly indicate that it is off-aircraft (e.g., “Functional check of pack overheat switch (off-aircraft)” or “Remove pack overheat switch for functional check”).

The interval is usually counted from the manufacturing date of the component, from first installation on the aircraft, or as specified by the manufacturer, and thereafter from the date of previous task accomplishment on the component.

Note: Where an expiry date is applied by the vendor, the operator may seek agreement from the competent authority to change the expiry date to reflect the MRBR task interval.

Removable Structural Components (RSC) Tasks

Repairs to Removable Structural Components may include structure on removable structural parts or assemblies that can be exchanged from one aircraft to another, such as door assemblies and flight control surfaces. If the transfer between aircraft is not appropiately controlled, it may result in a different utilization profile than the airframe the RSC is installed on.

Some requirements may be component-specific, primarily:

• Airworthiness Directives (ADs)

• Airworthiness Limitations, such as Damage Tolerance (DT) and Widespread Fatigue Damage (WFD) requirements

• Major repairs/alterations

Not all these tasks require component-level tracking, provided the RSC remains with the same aircraft. Tracking becomes essential when the component is transferred between aircraft.

In practice, many OEMs (e.g., Airbus, Boeing) provide a RSC Baseline List in the MPD, ALS, or supporting documents so operators know which RSCs require component-level control. Operators may review the baseline list and can add or subtract PNs based on their internal processes, experience and specific requirements.

Reliability Program Tasks

When an Aircraft Maintenance Program is based on MSG-3, it includes a Reliability Program to monitor component failures. This means that components may be tracked at component level due to reliability reasons, particularly when high removal rates, repetitive failures, or operational safety impact are identified through the operator’s Reliability Program.

Serialization

The approved rules for serialization applies only to parts that require individual traceability for continued airworthiness, such as critical parts or parts with life limits that can move between aircraft. The requirement to manage intervals at component level does not necessarily lead to serialization of these components.

For parts that do not meet these criteria, the operator may still use serialization or alternative methods, such as electronic tagging or bar coding, under an approved procedure to help track component intervals.

Conclusion

Control of maintenance tasks at the component level adds complexity and is more prone to errors compared to aircraft-level task management. Therefore, component-level tracking should be applied selectively and only when necessary. This includes tasks clearly specified in the Instructions for Continuing Airworthiness (ICAs), regulatory requirements such as Airworthiness Limitations (ALS) and Airworthiness Directives (ADs) on structural items that are transferred between aircraft, and tasks identified through the operator’s Reliability Program due to high removal rates, repetitive failures, or operational safety impact.

Component-level tracking may also be introduced for maintenance convenience, for example when splitting tasks across different ground times allows operators to distribute workload more efficiently and minimize aircraft downtime. However, this practice can be avoided by organizing tasks by zones rather than by associating maintenance to individual components.

Additionally, there may be other situations, such as warranty, insurance, or lessor requirements, where component-level tracking is established to meet contractual or commercial conditions. For all other components, aircraft-level maintenance tasks, combined with proper monitoring through the Reliability Program, are generally sufficient to ensure continuing airworthiness and efficiency.

In future articles, we’ll dive deeper into the Robbery Procedure—how components are properly tracked and moved between aircraft—and how to determine a component’s utilization profile when individual usage in different aircraft haven’t been recorded. Stay tuned!

These insights are just a glimpse of the essential procedures covered in our Aircraft Maintenance Programs (Advanced Expert) course. Master industry-leading practices, elevate your career, and become a recognized expert.