When should maintainability be considered during mechanical design?

Maintainability should be considered from the earliest stages of mechanical design, not as an afterthought once the core engineering decisions have already been made. The reasoning is straightforward: the choices that most affect how easy a system is to maintain, such as component placement, fastener selection, and access routing, are made long before a prototype is built. This article works through the key questions engineers and project leads face when trying to build maintainability into a design from the ground up.

Why is maintainability harder to retrofit than to design in?

Retrofitting maintainability is difficult because the design decisions that most affect access, serviceability, and repair time are deeply embedded in a system’s architecture. Changing them after the fact often requires reworking structural geometry, rerouting fluid or electrical paths, or redesigning interfaces that other components depend on. The cost and disruption of late-stage changes scale quickly.

When a mechanical system is designed without maintenance in mind, engineers later discover that serviceable components are buried behind structural members, that standard tooling cannot reach fasteners, or that replacing a single wearing part requires partial disassembly of surrounding assemblies. Each of these problems has a root cause in an early design decision, and each fix demands revisiting work that was already validated and signed off.

In high-complexity environments like aero engine development, this problem is particularly acute. Engine architectures are tightly packaged, and the spatial relationships between components are fixed early in the design cycle. If a bearing or seal is positioned without accounting for how a technician will reach it in service, the correction may require changes to the surrounding casing geometry, which ripples through stress analysis, thermal modeling, and manufacturing drawings.

The earlier a maintainability requirement is introduced, the cheaper it is to satisfy. Addressing it during concept selection costs relatively little. Addressing it during detailed design is more expensive. Addressing it after a prototype has been built is expensive. Addressing it after field deployment can be prohibitively costly, both financially and in terms of fleet availability.

What design decisions have the biggest impact on maintainability?

The design decisions with the greatest impact on maintainability are those that govern physical access, component replaceability, and the standardization of interfaces. These choices determine whether a technician can reach, remove, inspect, and reinstall a component within an acceptable time and without specialized tooling.

Access is the most fundamental factor. A component that fails frequently but is positioned where it can be reached quickly imposes far less maintenance burden than a rarely failing component that requires extensive disassembly to reach. This means that during layout and packaging, the expected service frequency of each component should influence its position relative to access panels and service ports.

Fastener selection and standardization also carry significant weight. Designs that use a large variety of fastener sizes and types increase the tooling a technician must carry and raise the risk of assembly errors during reassembly. Reducing fastener variety, specifying tool-accessible orientations, and avoiding fasteners in blind locations all reduce mean time to repair.

Component modularity shapes how much of a system must be disturbed to address a single failure. When wearing or high-probability-of-failure parts are grouped into discrete, self-contained modules with clean interfaces, they can be swapped without touching unrelated assemblies. This approach is widely applied in gas turbine design, where combustor liners, turbine blades, and bearing cartridges are treated as line-replaceable units with defined removal and installation procedures.

Material and surface treatment choices also affect long-term maintainability. Corrosion-prone materials in service-exposed locations create inspection and treatment requirements that compound over time. Selecting materials that tolerate the expected environment reduces the maintenance burden across the service life of the system.

How does maintainability relate to reliability and testability in engineering?

Maintainability, reliability, and testability are distinct but interdependent engineering properties. Reliability describes how long a system operates without failure. Maintainability describes how quickly and easily it can be restored after a failure occurs. Testability describes how effectively the system supports the detection and isolation of faults. Together, they determine the overall availability of a system.

A highly reliable system that is difficult to maintain may still achieve acceptable availability if failures are rare enough. But as systems age, reliability typically degrades, and maintainability becomes the dominant factor in keeping availability within acceptable bounds. Designing for high reliability without considering maintainability is a strategy that works only for a limited portion of a system’s service life.

Testability connects to both. A system that cannot be effectively tested, either during development or in service, will have undetected faults that accumulate until they cause failures. Testability requires that sensors, measurement points, and diagnostic interfaces be designed in from the start. In complex rotating machinery, this means specifying instrumentation access during the design phase rather than adding measurement taps as an afterthought.

In engineering practice, these three properties are often addressed together under the umbrella of Reliability, Maintainability, and Testability (RMT) analysis. The interactions between them mean that trade-offs must be made deliberately. Improving one at the expense of another without quantifying the effect on system availability leads to designs that perform poorly in service, even if they meet individual subsystem specifications.

At what stage of the design lifecycle should maintainability reviews occur?

Maintainability reviews should occur at every major gate in the design lifecycle, beginning at concept selection and continuing through detailed design, prototype validation, and pre-production. The earlier reviews are the most consequential because they address architectural decisions that are difficult to reverse. Later reviews confirm that earlier decisions have been correctly implemented.

During concept selection, the review should evaluate whether each candidate architecture supports the maintenance philosophy intended for the system. For a field-deployed machine, this means assessing whether the concept allows maintenance to be performed with the tools, skills, and time available in the intended operating environment.

During preliminary design, maintainability reviews should assess component placement, access routing, and the feasibility of planned maintenance tasks. At this stage, three-dimensional models can be used to simulate maintenance procedures, checking whether a technician’s hands and tools can physically reach the required locations without interference.

During detailed design, the review shifts to specifics: fastener types and orientations, connector keying and labeling, torque access for tools, and the completeness of maintenance documentation. This is also the stage at which engineering testing services can be used to validate that instrumentation and diagnostic access points are functional and that maintenance procedures can be executed as written.

After prototype build, a hands-on maintainability demonstration is valuable. Having a technician unfamiliar with the design attempt to perform representative maintenance tasks reveals gaps that simulations and reviews miss. The findings from this exercise should feed directly back into the design before production drawings are finalized.

What are the consequences of ignoring maintainability during design?

Ignoring maintainability during design results in higher lifecycle costs, reduced system availability, and increased risk of maintenance-induced failures. These consequences compound over time and are often far more expensive than the investment that would have been required to address maintainability during development.

Higher maintenance labor costs are the most direct consequence. When components are difficult to access or replace, maintenance tasks take longer. In aviation and power generation, where downtime has a direct financial cost, extended maintenance windows translate immediately into lost revenue or operational capacity.

Maintenance-induced failures represent a less obvious but serious risk. When maintenance tasks are difficult to execute, the probability of errors during reassembly increases. Incorrectly torqued fasteners, misrouted seals, and reversed connectors are more likely when technicians are working in constrained conditions under time pressure. These errors can cause failures that would not have occurred if the original component had simply been left in place.

Over the full service life of a system, poor maintainability can also drive premature retirement. When the cost and complexity of maintaining an aging system exceeds the cost of replacement, operators will retire equipment earlier than its structural life would otherwise require. This means that the full value of the engineering investment in the original design is never recovered.

In regulated industries, there are compliance dimensions as well. Maintenance programs for aircraft engines and gas turbines are subject to regulatory approval, and designs that cannot support the required inspection intervals or replacement tasks may face certification challenges that delay entry into service.

How AneCom supports maintainability in mechanical design

AneCom AeroTest works with engineers and development teams at the point where maintainability decisions are most consequential: during experimental validation and component testing. By providing rigorous test data early in the development cycle, AneCom helps teams make informed design choices before architectural decisions are locked in.

Aerothermal component testing for compressors, combustors, and turbine assemblies, generating the performance and durability data needed to support design-for-maintainability decisions
Non-destructive testing services that support both in-service inspection programs and the validation of maintenance procedures during development
Instrumentation and assembly expertise applied to test vehicles, including the design of measurement access points that reflect real-world service requirements
Testing of fan systems and multistage compressors in conditions that replicate operational environments, providing data that informs both reliability predictions and maintenance interval planning

Whether you are in the concept phase of a new aero engine program or validating a design update on an existing gas turbine component, AneCom’s testing and engineering services provide the technical foundation for sound maintainability decisions. Contact AneCom to discuss how experimental testing can be integrated into your development process.