RCM Analysis - MEI Calculation (Step 5)

This RCM online tutorial describes how to calculate the MEI in an RCM Analysis using the fifth guided step.

This aspect of the RCM analysis relates to question six (last part) of the seven RCM questions: What can be done to predict or prevent each failure? This step addresses the economics of maintenance in terms of MEI, risk reduction, and residual risk.

In the fifth and final guided step, you verify whether the preventive maintenance tasks defined in the previous steps actually drive value and reduce the probability of negative effects of an equipment failure.

How MEI is Calculated

There are two ways to assess whether preventive maintenance is driving value:

Compare the "do-maintenance" situation against the "no-maintenance" situation in terms of total annual cost.
Calculate the Maintenance Efficiency Index (MEI): the ratio of risk reduction achieved by the maintenance tasks to the cost of those tasks.

Both approaches rely on the same underlying data. A key input is the residual risk — the remaining probability of equipment failure even when preventive maintenance is performed. This is expressed as the Estimated Time Between Consequences (ETBC): the estimated time between failure events that still occur despite the maintenance strategy.

The MEI formula is:

(Base risk − Residual risk) ÷ Annual maintenance cost

An MEI above 1 indicates a beneficial maintenance strategy. MEI values of 2 or above represent more robust strategies. In IMS RCM, the MEI threshold that triggers automatic approval can be configured at site or unit level (see MEI Threshold below).

Entering the ETBC Value

In Step 5, the only value you need to enter is the ETBC.

The MEI calculation screen pre-populates the financial data from earlier steps: the Total annual POC (cost of the maintenance tasks) and the Total economic risk without maintenance (the base risk). Entering the ETBC value drives the calculation of the remaining fields, including Total economic risk with maintenance (residual risk) and Total annual cost with maintenance.

Once the ETBC is entered:

The residual risk level is determined (displayed as a letter code, for example, N).
The MEI is calculated automatically.
If the MEI is at or above the configured threshold, the analysis is automatically marked as Approved.
If a maintenance task is flagged as IsMandatory, the analysis is also automatically approved regardless of the MEI value.

When done, click Finish to complete the guided steps.

Note
You can map RCM RAM results to corresponding Corp Risk values. Corporate Risk is the combination of the severity of the operational, financial, safety, and environmental consequences and the probability (likelihood) of an asset failure. Using criticality, a fixed probability is applied, and over time, as the probability rises, so does the risk, though the criticality stays the same. RCM uses this criticality to determine which maintenance tasks are necessary and cost-effective.
Contact Cenosco support to enable the functionality and do the mapping for your site.

Low MEI Investigation

If the MEI is low or zero at the end of an RCM analysis, the following fields are most relevant to investigate:

Low MEI values typically originate from:

Low criticality (annual risk value): As a rule of thumb, the annual maintenance spend should not exceed approximately one-third of the annual risk value. If the criticality is low, the ceiling for justifiable maintenance cost is also low.
High or zero annual maintenance cost (POC): A high POC should be reviewed against task cost and frequency data. A zero POC — which results in a zero MEI — is usually caused by missing task data, such as no interval defined.
High residual risk (low ETBC): The ETBC should be considerably larger than the Estimated Time Between Failures (ETBF). A low ETBC suggests the maintenance strategy is not effectively reducing failure consequences.

MEI Threshold

Different organizations may apply different MEI levels to approve an RCM analysis. While the baseline approval threshold is MEI ≥ 1, experience has shown that MEI ≥ 2 represents a more robust strategy. Some organizations apply a threshold of MEI > 5.

In IMS RCM, the MEI threshold can be configured at both unit level and site level via Settings > Company > Toplevel > (select a unit in the site hierarchy tree) > Details.

The threshold hierarchy works as follows:

If a threshold is configured at unit level, it takes precedence and is shown as the MEI Unit threshold in the analysis.
If no unit-level threshold is set, the site-level threshold is used and shown as the MEI Site threshold.
If neither is configured, a default threshold of 1 applies.

Manual Approval

If the MEI is below the threshold but there are strong justifications for the maintenance strategy, you can manually approve the analysis. A track list and free text field are available to record the rationale.

Residual Risk and RCM Question 7

The residual risk level also relates to question seven of the seven RCM questions: What should be done if a suitable proactive task cannot be found?

Ideally, the residual risk should be at level M or lower. If the residual risk is at MH or higher, additional actions are required — such as a redesign involving other equipment. Any such recommendations can be recorded in the free text field of the MEI calculation area and should also be included in the final RCM study report.

Copying Analyses from Another Tag

When an RCM Analysis is copied from one tag to another, an option to replace the Failure Mode and Task PLE with the PLE of the target System is offered. If selected, the MEI is recalculated based on the the target System’s PLE. If the option is left unselected, the PLE from the original tag is used, and the MEI is calculated based on it.

Instruction video

For a walkthrough of the guided steps, see RCM Analysis Guided Steps - Episode 7.

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