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Updated on 11/7/2019
Relyence User Guide
Introduction to Maintainability Predictions
Direct link to topic in this publication:

Introduction to Maintainability Predictions

Maintainability predictions are performed in order to assess various repair and maintenance related metrics. By entering the tasks and activities related to repairing and/or maintaining your system, you can use the widely accepted standard, MIL-HDBK-472: Military Standardization Handbook: Maintainability Prediction, to compute a range of predicted maintenance parameters. The objective of a maintainability prediction is to assess system repair and maintenance activities in order to minimize system downtime. The ultimate goal is to ensure that you are meeting your availability objectives.

Performing a maintainability prediction analysis begins by defining all your system components and then determining all their associated repair and maintenance tasks and activities. You can begin your maintainability prediction at any time, even prior to your product being built or manufactured, and continually refine as your system design stabilizes and parameters become more finalized. One advantageous use of maintainability prediction analysis is to evaluate your product while in the design phase in order to look for potential areas of concern related to downtime and minimize their impact. 

We recommend going through Getting Started with Relyence Maintainability Prediction as a starting point for learning Relyence Maintainability Prediction. From there, you can proceed to building your own analyses. The following process is intended to be a starting point; you can adapt it as required for your needs.

Relyence Maintainability Prediction and Relyence Reliability Prediction integrate seamlessly and provide an easy way to manage all your prediction data and Analyses. If you start with a Reliability Prediction analysis, you can define your system structure there and compute failure rates that are then available for use in Maintainability Prediction.

1. Define your Analysis Tree

To begin your Maintainability Prediction analysis, create the hierarchical representation of your product. As in the case of our Example drone used in the tutorial, we broke the drone into the overall Quadcopter Drone, and the subsystems Motherboard, GPS, and Ground Controller. 

By defining your product in this hierarchical manner, you can see the contributions of the separate subsystems to the overall failure rate and more effectively spend your time working on areas that provide the most reliability improvement.

In Relyence Maintainability Prediction, use the Analysis Tree to define your products and its subsystems.

If you are also using Relyence Reliability Prediction, or another Relyence Product where you have defined your Analysis Tree, that tree is shared with Maintainability Prediction if part of the same Analysis. So, you only have to define your Analysis Tree once within a single Relyence Analysis.

3. Add your parts, if desired

If you want to perform your maintainability prediction down to the device, or part, level, you add all the parts that make up each subsystem to your Analysis Tree. For example, if you are looking at a Motherboard, you add in each and every component on that Motherboard.  You must know the types of all your parts (resistor, capacitor, IC, etc.) and enter these in order to perform a maintainability prediction. 

Once again, if you are using Relyence Reliability Prediction and have entered all your Parts there, they are automatically available in Relyence Maintainability Prediction. You can enter your Analysis Tree and Parts using Relyence Reliability Prediction and then move to Relyence Maintainability Prediction. 

3. Define your Tasks, Task Groups, FD&I Outputs, and Maintainability Groups

Maintainability Predictions are based on data related to your repair and maintenance activities and their associated data - such as time, number of people needed to perform, and frequency.  This data are the building blocks that are then used to define the maintenance actions required to repair or maintain your system.

Maintenance Tasks are single steps that are part of a repair activity, such as removing a screw to start replacing a component. There are a number of tasks predefined in the Relyence Maintainability Task Library that are found in the MIL-HDBK-472 standard. You can use these predefined tasks, as well as add to them by defining your own tasks.

A Maintenance Task Group represents a set of tasks that are performed together as part of a repair activity. For example, the replacement of a failed component in your system may include a set of steps such as: remove 4 screws, remove defective component, replace with new component, replace 4 screws.

FD&I (Fault Detection and Isolation) Outputs are defined in MIL-HDBK-472 as "indications, symptoms, readouts, or the results of manual procedures which separately or in combination, identify to the maintenance technician the procedure to be followed." The maintenance actions taken in response to an observed FD&I output are then cataloged in the FD&I Output Library.

Maintainability Groups are only used if you are using MIL-HDBK-472 Procedure 5A. Maintainability Groups enable you to describe any number of defined groups during fault isolation procedures, such as whether there is isolation to a single replaceable item (RI), a group of RIs, or an iterative approach for isolation is employed. Additional information, such as access to removable items and if reassembly is required for checkout are also included in the Maintainability Group definition.

4. Enter repair and maintenance related activities

Once you have defined all your task related data, you then move onto defining the maintenance activities associated with the repair of your system. Depending on how detailed you want the analysis to be, you define the tasks, task groups, or FD&I outputs with the elements of your Analysis Tree. You can define repair elements for all components of your tree, or just those you are interested in analyzing.

5. Compute repair and maintenance metrics

Once the data entry is complete, you perform calculations. The list of calculations that can be computed based on MIL-HDBK-472 are extensive, and you can select those that you prefer.

6. Evaluate repair and maintenance metrics

Once calculations are complete, you can review the repair metrics to see if there are areas that are of concern. If so, you may want to go back and evaluate those potential problem areas and try out different options to improve your repair times. The more you lower the overall repair times of your product, the better your system uptime will be.

7. Continue to refine your analysis

As your product design evolves, update your maintainability prediction to reflect changes that impact repair and maintenance. You can also look at actual repair and maintenance activities of your product once deployed to evaluate if your maintainability prediction analysis has proven accurate. If not, consider how the lessons learned from your field experience can be used to aid in future maintainability predictions.