airworthiness directive (AD) and the CMR document will be revised to include the change.
e. New CMRs that are unrelated to in-service events may be created and they should be documented and approved by the governing ACO. New CMRs can arise in situations such as:
(1) Certification of design changes, or
(2) Updates to the applicant’s certification compliance documentation. These may result from regulation changes, AD actions on similar systems or airplanes, awareness of additional hazardous or catastrophic failure conditions, revised failure rates, consideration of extended service goals, etc.
Original signed by Ali Bahrami Ali Bahrami Manager, Transport Airplane Directorate Aircraft Certification Service 13
Appendix 1 APPENDIX 1 Supplemental Guidance for CMR Use
1. The FAA intends that the manufacturer chooses a system design that minimizes the number of significant latent failures, with the goal being no such failures if it is practical to do so. A practical and reliable monitoring and/or warning system should be considered as the first means to expose the significant latent failure. If the cost of adding practical and reliable monitoring and/or warning to a system is large, and the added maintenance cost of a CMR is small, addition of a CMR may be the solution of choice for both the type certificate applicant and the operator, provided all applicable regulations are met. Substituting a CMR with a MSG-3 task does not necessarily improve maintenance costs.
2. A decision to create a CMR may include a trade-off of the cost, weight, or complexity of providing an alerting mechanism or device that will expose the latent failure, versus the requirement for the operator to conduct a maintenance or inspection task at fixed intervals.
3. The following points should be considered in any decision to create a CMR:
a. What is the magnitude of the changes to the system and/or airplane needed to add a reliable monitoring or warning device that would expose the hidden failure? What is the cost in added system complexity?
b. Is it possible to introduce a self-test on power-up?
c. Is the monitoring and warning system reliable? False warnings must be considered, as well as a lack of warnings.
d. Does the monitoring or warning system itself need a CMR due to its latent failure potential?
e. Is the CMR task reasonable, considering all aspects of the failure condition that the task is intended to address?
f. How long (or short) is the CMR task interval?
g. Is the proposed CMR task labor intensive or time consuming? Can it be done without having to "gain access" and/or without workstands? Without test equipment? Can the CMR task be done without removing equipment from the airplane? Without having to re-adjust equipment? Without leak checks and/or engine runs?
h. Can a simple visual inspection be used instead of a complex one? Can a simple operational check suffice in lieu of a formal functional check against measured requirements?
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Appendix 1
i. Is there "added value" to the proposed task (i.e., will the proposed task do more harm than good if the airplane must be continually inspected)?
j. Have all alternatives been evaluated?
A1-2