Introduction to Certification Maintenance Requirements (CMRS)

Posted by on in Regulatory
  • Font size: Larger Smaller
  • Hits: 128

Sofema Online (SOL) considers the role of Certification Maintenance.

Discuss the History of Certification Maintenance Requirements (CMR) related to FAA and EASA type certification of aircraft, and to consider the methodology and challenges related System Safety Assessment Process.


The Certification Maintenance Requirements (CMR) are regulations established by the Federal Aviation Administration (FAA) in the United States and the European Union Aviation Safety Agency (EASA) in Europe.

The concept of CMRs evolved over time to ensure that certified aircraft maintain their airworthiness throughout their operational life.

The European Union Aviation Safety Agency (formerly the Joint Aviation Authorities) was established in 2002 to harmonize aviation regulations across Europe. EASA adopted the CMR concept as part of its certification process.

It aligns with the FAA's approach, but with certain differences to accommodate regional variations.

>> CMRs define the ongoing maintenance and inspection requirements for aircraft certified under their respective jurisdictions.

Certification Maintenance Requirements (CMR) Definition.

>> A CMR is a required scheduled maintenance task established during the design certification of the airplane systems as an operating limitation of the type certificate (TC) or supplemental type certificate (STC).

>> The CMRs are a subset of the instructions for continued airworthiness identified during the certification process.

>> A CMR usually results from a formal, numerical analysis conducted to show compliance with the requirements applicable to catastrophic and hazardous failure conditions, as defined below.

Note - Compliance may also result from a qualitative, engineering judgment-based analysis.

>> The CMRs are required tasks, and associated intervals, developed to achieve compliance with § 25.1309 and other regulations requiring safety analyses (such as §§ 25.671, 25.783, 25.901, and 25.933).

>> A CMR is intended to detect safety-significant latent failures that would, in combination with one or more other specific failures or events, result in a hazardous or catastrophic failure condition.

>> A CMR can also be used to establish a required task to detect an impending wear-out of an item whose failure is associated with a hazardous or catastrophic failure condition.

Note - It is important to note that CMRs are derived from a fundamentally different analysis process than the maintenance tasks and intervals that result from the MSG-3 analysis associated with MRB activities (if the MRB process is used).

>> Although both types of analysis may produce equivalent maintenance tasks and intervals, it is not always appropriate to substitute a CMR with an MSG-3 task.

>> The CMRs verify that a certain failure has or has not occurred, indicate that repairs are necessary if the item has failed, or identify the need to inspect for impending failures (e.g., heavy wear or leakage).

>> Because the exposure time to a latent failure is a key element in the calculations used in a safety analysis, limiting the exposure time will have a significant effect on the resultant overall failure probability of the system.

>>The intervals for CMR tasks should be designated in terms of flight hours, cycles, or calendar time, as appropriate.

Deriving CMR’s during System Safety Assessment Process

During the System Safety Assessment (SSA) process in the aircraft type certification, Certification Maintenance Requirements (CMRs) are determined based on a thorough analysis and evaluation of the system's safety requirements.

>> The first step in identifying CMRs is to conduct a SSA.

>> The SSA process is typically carried out by the design organization under the oversight of aviation regulatory authorities, like the Federal Aviation Administration (FAA) in the United States, or the European Union Aviation Safety Agency (EASA) in Europe.

>> A As part of the SSA, a Failure Modes and Effects Analysis (FMEA) is conducted. This process identifies potential failure modes of the system, the effects of those failures on the overall aircraft system, and assesses the risk of each failure.

>> Each identified failure mode is classified according to the severity of its effects, ranging from "No Safety Effect" to "Catastrophic."

>> The most severe failure modes that could result in catastrophic outcomes are subjected to a Criticality Analysis, which assesses the probability of occurrence. The criticality of a failure mode is determined by both its severity and its probability.

>> Any system or component that, upon failure, could lead to a catastrophic outcome and for which the failure condition is not immediately apparent to the flight crew, is a candidate for CMR.

   The aim is to determine maintenance tasks that can prevent these latent failure conditions from going unnoticed.

Establishing CMR’s

>> Based on the analysis, CMRs are established. These are specific maintenance tasks that need to be carried out at defined intervals to ensure that the risk of catastrophic failure remains acceptably low throughout the operational life of the aircraft.

>> Once the CMRs are established, they are listed in a CMR document. This document becomes part of the aircraft's Instructions for Continued Airworthiness (ICA), which is a manual provided by the aircraft manufacturer and approved by the regulatory authority.

>> The regulatory authorities review the CMR document and, if they agree with the findings and recommendations, they approve it.

The aircraft operator must then follow the CMRs as part of their regular maintenance schedule to maintain the airworthiness of the aircraft

Next Steps

>> Follow this link to the SAS Library to find & Download related documents for Free

Sofema Aviation Services ( offers training to cover CS 25 System Safety Assessments – please see the following link 

Type Certification System Safety Assessment – 5 Days

For additional questions or comments – please email [email protected]

Last modified on