Historic or Anticipated? Fleet Average or Individual? All About Aircraft Utilization

Maintenance programs are built around assumptions about how an aircraft is used. When actual operations deviate from these assumptions, maintenance tasks may be missed or performed unnecessarily. Understanding aircraft utilization, monitoring it against expected limits, and applying low-utilization recommendations are key steps for safe, reliable and cost-effective operations.

This is not just a matter of efficiency — it is a critical safety issue. Several incidents and accidents have been attributed to low utilization not being reflected in the approved Aircraft Maintenance Program (AMP).

Confusion often arises among operators regarding the difference between historic and anticipated utilization, fleet-wide versus individual aircraft utilization, and specific regulatory requirements — such as the EASA requirement to include a tolerance of no more than 25% in the stated values within the approved AMP.

MRBR and the Utilization Envelope

The Maintenance Review Board Report (MRBR) and MSG-3 analysis tasking requirements are developed assuming a specific utilization envelope. Task intervals identified in the MRBR are valid only within this envelope, which is based on anticipated average annual utilization.

For instance, an MRBR may assume that an aircraft is planned to fly 2,500–3,000 Flight Hours and 1,200–1,400 Flight Cycles per year. MRBR task intervals are based on this assumption.

Aircraft operating outside this envelope — for example, with much lower or higher usage than anticipated — may require additional guidance. Type Certificate Holders (TCHs) are responsible to provide these recommendations.

Historic vs. Anticipated Utilization

MRBR/MSG-3 intervals are not intended to be retroactively applied based on historic utilization. It's common that operators mistakenly use historical usage to define maintenance tasks. While historic data is valuable for trend analysis, MRBR assumes a predictable utilization going forward. Deviations from this assumed utilization — whether higher or lower — can lead to over-maintenance, under-maintenance, or non-compliance.

If anticipated utilization for the maintenance program review is calculated without input from the Commercial/Route Planning teams, it can result in inaccurate values that are disconnected from the aircraft’s actual utilization projections — except in cases where flight operations are highly regular and predictable.

Fleet vs. Individual Aircraft Utilization

Maintenance programs are often developed using fleet-average utilization to simplify planning. This works well for homogeneous operations but may not reflect the reality of individual aircraft that operate differently due to routes, missions, or seasonal schedules. For aircraft that deviate from the fleet average, maintenance intervals may require adjustment. Failing to account for individual aircraft utilization can result in deviations from the MRBR-defined utilization envelope, potentially leading to risks and regulatory non-compliance.

EASA About Utilization

EASA and equivalent regulatory environments require operators to state the anticipated annual aircraft utilization in the approved AMP and to include a tolerance of no more than ±25%.

Where anticipated utilization cannot be defined, or details of aircraft utilization are not available in the TCH’s Instructions for Continued Airworthiness (ICA), calendar-based limits must also be incorporated. This ensures that tasks dependent on time degradation are performed, even when flight activity is irregular or unpredictable.

The Importance of Monitoring

Continuous monitoring of actual aircraft utilization against anticipated values and regulatory tolerances is essential to:

• Detect deviations early at both fleet and individual aircraft levels.

• Adjust maintenance intervals proactively to prevent over- or under-maintenance.

• Maintain compliance with regulatory requirements and AMP specifications.

An AMP remains effective when it is:

• Based on realistic anticipated utilization values, and

• Supported by formal evaluation through AMP effectiveness analysis.

Conclusion

Understanding aircraft utilization, differentiating between historic and anticipated usage, and considering fleet versus individual aircraft differences are fundamental for safe and compliant maintenance programs. Operators must clearly define anticipated utilization in the AMP, include the required tolerance, coordinate across teams, and monitor usage continuously. These practices ensure that maintenance tasks are performed on time to detect degradation and failures, and safeguarding both safety and operational reliability.

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