Maintenance Phase Blocks

A maintenance phase represents the portion of the overall mission time when the system is down and maintenance actions are being performed on some or all of its components. A maintenance phase block is defined by (linked to) a maintenance template. This template can be thought of as a list of the specific components (blocks) that are designated to undergo inspection, repair or replacement during the maintenance phase, along with their maintenance priority order. For example, if blocks A, B and C are to undergo maintenance during a specific phase, they are placed in a maintenance template in a sequence that defines the priority for completing each task. If three repair crews and three spare parts are available at the same time, the tasks on A, B and C will be carried out simultaneously. However, if only one crew is available, the tasks will be carried out based on the priority order defined in the template.

Note: Maintenance tasks defined in the RBDs represented by operational phase blocks may also be carried out. (See Maintenance Phases and Maintenance Tasks in Diagrams.)

Given that many aspects of maintenance can be probabilistically defined (e.g., the time to repair, the time to obtain a spare part, etc.), the duration of a maintenance phase is not fixed; the phase lasts as long as it takes to complete all of the tasks specified in the maintenance template.

Maintenance phase blocks can have unlimited incoming connections and a single outgoing connection.

You can add a maintenance phase block to a phase diagram by choosing Phase > Phase > Add Maintenance Phase.

To open a maintenance phase block that already appears in the phase diagram, double-click the block or choose Phase > Settings > Block Properties to open the Phase Properties window.

The following properties are available to configure a maintenance phase block:

Phase name and Description: Each block is given a default name that is determined based on the block type's default name format. You can type new text either instead of or in addition to the default name. You can change the default names by choosing File > Manage Repository > Define Default Names.

The Name field must be populated. Description text is optional. Note that an asterisk is used (*) to represent default block names. The block name that is displayed in the diagram will replace the asterisk with the block's default name; this allows the block name to be updated dynamically.

Phase Properties
- Maintenance Template allows you to select a maintenance template from the current project that you want the phase to represent. Once you have assigned a maintenance template, the number of blocks in the maintenance template is also shown.
- Interval maintenance threshold allows you to specify the age interval when preventive or inspection tasks based on system or item age intervals (fixed or dynamic) will be performed. This can help you optimize the resources allocated to repair the system during a maintenance phase by performing preventive maintenance or inspections when the system when the system is already down in a maintenance phase. This property provides the ability to add some flexibility to the timing of scheduled preventive maintenance actions and/or inspections.

For example, imagine that a preventive maintenance action is scheduled for a car (e.g., an oil change, tire rotation, etc.) at 60,000 miles, but a system downing event occurs at 55,000 miles. The Interval Maintenance Threshold allows you to stipulate that the preventive task will be performed upon a system downing event as long as a specified percentage of that 60,000 miles has passed. If, in this case, you specify an Interval Maintenance Threshold of 0.9, the preventive task will be performed if a system downing event occurs after at least 54,000 miles (60,000 miles x 0.9 = 54,000 miles). Thus, the downing event at 55,000 miles will trigger the preventive task. On the other hand, if you were to specify an Interval Maintenance Threshold of 0.95, the preventive task would not be performed upon the system downing event at 55,000, because that event preceded the threshold age of 57,000 miles (60,000 miles x 0.95 = 57,000 miles).

Identifiers: The Comments field allows you to enter additional information about the block.

The Active Phase drop-down list at the bottom of the window allows you to specify another phase block that you want to edit without the need to close and reopen the Phase Properties window. This option works in exactly the same way as the Active Block feature in the Block Properties window.

Note: A maintenance phase will not end until all components are restored. Therefore, if any failed block does not have a task that restores it, the maintenance phase will not end.

Maintenance Phases and Maintenance Tasks in Diagrams

Not all maintenance performed during simulation of a phase diagram is necessarily performed during maintenance phases. There may also be tasks assigned to the blocks within a simulation RBD represented by an operational phase block.

Scheduled tasks that are assigned to blocks within the simulation RBD are performed as defined, even if they bring the system down.
For a block that does not bring the system down when it fails, the assigned corrective task (if any) is also performed as defined.
If the block failure brings the system down, then the connections in the phase diagram determine what happens:
- If a failure path is defined, the current phase is interrupted and the phase linked to the failure path begins. (This could be a maintenance or another operational phase.) Maintenance properties defined in this new phase now apply. For the block that just failed, the new corrective maintenance properties apply. For other blocks with maintenance in progress, the rules for interrupted maintenances apply.
- If no failure path is defined, then the phase continues until its specified duration is completed. In this case, the tasks apply as defined in the RBD.