CMR (Part II): Coordinating, Categorizing, and Managing Certification Maintenance Requirements

As discusses on CMR (Part I) of this article series, Certification Maintenance Requirements (CMRs) are derived from a System Safety Analysis (SSA) that identifies safety-significant latent failures in aircraft systems. Candidate Certification Maintenance Requirements (CCMRs) are the initial proposed scheduled tasks that emerge from this SSA process, before formal review and approval.

Coordinating CMRs

The Certification Maintenance Coordination Committee (CMCC) oversees the selection and approval of CMRs. This committee includes manufacturer representatives, operators, Certification Authority (CA) specialists, and the Maintenance Review Board (MRB) Chairperson.

Each Candidate Certification Maintenance Requirement (CCMR) is reviewed against existing safety-classified MRB tasks:

• If an MRB task already meets the purpose, interval, and scope of the CCMR, the CMCC coordinates with the Industry Steering Committee (ISC). If accepted, the MRB task covers the CCMR and is incorporated into the MRB report (MRBR), with safeguards to avoid that future optimization/evolution MRBR exercise change the scope or the interval that is required by the corresponding CCMR.

• If the ISC does not accept the MRB task as covering the CCMR, the CCMR is submitted directly to the Certification Authority (CA) for approval as a formal CMR.

Any new or changed CMRs after certification must also be reviewed and approved by the CMCC and CA.

CMR Categorization

CMRs are functionally equivalent to Airworthiness Limitations (ALIs) and are typically included in the Airworthiness Limitations section. Most aircraft manufacturers define two types of CMRs, based on the sensitivity of the failure condition to interval escalation:

• One-Star CMRs (CMR*): mandatory tasks that cannot be escalated, changed, or deleted without approval of the State of Design Certification Authority.

• Two-Star CMRs (CMR**): mandatory tasks that cannot be changed or deleted without approval of the State of Design Certification Authority, but whose interval may be escalated with approval of the competent Certification Authority of the State of Registration, normally under an approved Reliability or Escalation Procedure.

Some manufacturers may use different terminology or symbols to distinguish CMR types.

Post-Certification Changes

CMR post-certification changes may only arise due to any of the following reasons:

• the world fleet service experience shows that certain assumptions regarding component failure rates made during the SSA were too conservative and new re-calculated failure rates demonstrate that the task interval may be changed,

• there are sufficient data basis for the relaxation of the CMR,

• the authority determines that the requirement must be more restrictive, or

• new CMR unrelated to in-service events arises due to:

  • certification of design changes, or

  • updates to the certification compliance documentation, e.g., due to regulation changes, AD actions on similar systems or aircraft, awareness of additional hazardous or catastrophic failure conditions, revised failure rates, consideration of extended DSG, etc

New or stricter requirements, such as interval de-escalations, are mandated through Airworthiness Directives (ADs). CMR relaxations, such as deletions or interval escalations, do not justify issuing an AD.

Exceptional Short-term Extension

An Exceptional Short-Term Extension is a one-time allowance to extend the interval of a maintenance task defined in the Airworthiness Limitations Section (ALS) for a specific aircraft. Not all Airworthiness Limitation tasks can be extended. Typically, the Type Certificate Holder (TCH) identifies in the ALS which tasks are eligible, along with the maximum allowable limits based on reliability data and safety considerations.

Once these eligible tasks and limits are published in the ALS, the responsibility for granting extensions lies with the competent authority, which may delegate this authority to the continuing airworthiness organization.

This mechanism should not be confused with the operator’s Permitted Variations for normal maintenance tasks, which apply only to non-mandatory tasks and do not constitute an extension of certified airworthiness limitations.

Conclusion

CMRs are one of several mechanisms that ensure compliance with the type certification basis, alongside other Airworthiness Limitations and Airworthiness Directives (ADs) that enforce them. Through structured review by the Certification Maintenance Coordination Committee (CMCC), integration with MRB tasks, and approval by the Certification Authority, CMRs maintain their effectiveness throughout the aircraft’s service life. By understanding how CMRs are managed, categorized, and modified, operators can ensure that maintenance tasks continue to mitigate safety-significant latent failures effectively.

For a full understanding of the CMR foundation and SSA, see CMR (Part I): Understanding Certification Maintenance Requirements and System Safety Analysis.

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