1.6.4 Failure monitoring and warning systems
Completion of a safety analysis, using the techniques described in 1.6.2.5 of this Part, may identify potential latent failures. Such failures should be identified to the flight crew by failure monitoring and warning systems. However, it is axiomatic that these systems should be practical and reliable, i.e. within the state of the art. A reliable system is one which will not result in either excessive failures of a genuine warning or excessive or untimely false warnings, which can sometimes be more hazardous than lack of provision for, or failures of, genuine but infrequent warnings. If a practicable and reliable monitoring and warning system cannot be provided, other means should be provided to detect significant latent failures, as described in the following paragraph.
1.6.5 Implementation of
certification maintenance requirements (CMRs)
1.6.5.1 To reduce or eliminate the hazardous consequences of undiscovered pre-existing failures, checks for such failures should be accomplished. These checks can be developed through the MRB process, system safety assessment or CCMC procedures and published as CMRs where it is necessary to identify significant latent failures. Some checks of this nature may be performed by flight crews. If this is the case, they will be incorporated as mandatory procedures in the flight manual. (As previously mentioned, current design philosophy is to eliminate CMRs from flight crew procedures in future designs and to limit CMRs to maintenance tasks.)
1.6.5.2 CMRs are developed using rational methods, such as quantitative analysis or service experience. The tasks are intended to be implemented concurrently with routine maintenance inspection tasks, i.e. tasks not associated with the design compliance process described in 1.6.1.2 above.
1.6.5.3 CMRs are produced by the organizations responsible for the type design and approved by the State of Design during the type certification process. CMRs are listed in the Type Certificate data sheet or equivalent document. In many cases, it is appropriate for the Type Certificate data sheet to make reference to another document where CMRs may be placed for convenience to the operator. For aircraft with aeroplane maintenance manuals formatted in accordance with Air Transport Association of America Specification 2200 (ATA 2200), formerly Specification 100 (ATA-100), CMRs can be included in Chapter 5 but are sometimes contained in the appropriate section of the ATA 100 maintenance planning data document (MPD) or in a separate airworthiness limitations manual.
1.6.6 Incorporation of airworthiness limitations and CMRs in maintenance programmes
1.6.6.1 From the previous text, it is apparent that CMRs are an integral part of the validation of the type design and are essential to continuing airworthiness, even though the same conclusion may be made in respect of other types of airworthiness limitations. During the approval of maintenance programmes (paragraph 1.6.1.1 of this Part refers), the State of Registry should ensure that CMRs and airworthiness limitations (including their associated intervals and tolerances as established by the State of Design) are included.
1.6.6.2 The State of Registry should not approve changes to airworthiness limitations without consulting with the State of Design. Some type designs may include approved procedures which allow the aircraft operator to vary airworthiness limitations task intervals (or limits). It is essential that any variation is completed in accordance with these procedures.
1.6.6.3 Based on service experience, it is normal practice for operators to develop maintenance programmes in terms of variation of task content and escalation of inspection and check intervals. Airworthiness limitations are to be excluded from this escalation process. It is strongly recommended that States of Registry ensure that:
a) airworthiness limitations are clearly identified as such in the maintenance programme; and
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