The Maintenance Programme reliability is obtained by calculating, for each selected MR, :
- the total number of executions
- the total number of executions with at least one additional work
- the total number of additional works
To calculate the maintenance programme reliability:
- Define the protocol (Maintenance Programme)
- Click on the "Calculate" button
Note: you can also define (optional) a period (since - up to) , include the MR currently canceled or replaced (only active MR unchecked) and NRC levels.
-> The following screen is displayed and include all selected MR analysis:
Post processing filters: The top band holds several commands:
- As a statistic analysis, the sampling size is important. To come to a conclusion on a particular MR, we should take the number of executions into consideration. With this post processing filter, you "can display" (checkbox) only or "highlight" (checkbox) the MR having a number of executions exceeding ("number of execution >") a specified number or having a rate of additional works ("Rate (%) of Additional Work >") exceeding a specified value. If a post processing filter is defined, then press "Apply filter" to filter / highlight as necessary.
- Report: print / preview the analysis as currently displayed on screen (with post processing filters)
Result grid:
- # Exec: Total number of executions
- # with AddW: Number of executions with at least one additional work
- # AddW: Number of additional works (for all executions)
What's next:
Once the main figures are calculated, the highlighted items should be analysed closely to evaluate if the repeat interval should be reduced or, if there is no or very few additional works, to evaluate if an escalation is appropriate. This analysis should be exposed in your approved procedures.
Escalation: To consider an escalation, the total number of executions should be significant (at least 15). The admissible rate of additional works should be reduced when the total number of executions is low (3% of additional works on a sample of 15 executions is not comfortable whereas 4% on a sample of 150 could be acceptable to consider an escalation). Except otherwise approved by the competent Authority, a maintenance requirement should not be escalated beyond the manufacturer's recommendations (as set forth in the approved maintenance planning documents or equivalent)
Degradation: When downgrading a repeat interval, make sure that an abnormal rate of additional works is not linked to extraordinary conditions like a resent delivery of second hand aircraft. The sample duration should also be long enough to cover at least 3 executions on the same aircraft (if the MR was executed 15 times on 15 different aircraft and resulted in a high rate of additional works, it is important to know if it was the first execution for each aircraft or if this MR has a long history before the sampling period)