(b)
Service experience. This aspect recognizes the use of relevant service or operating experience, such as fleet hours performance or reliability statistics, to demonstrate that compliance with the latest design standards may not contribute materially to the level of safety, and as such the use of other than the latest design standards may be appropriate. The service experience levels necessary to demonstrate the appropriate level of safety as they relate to the proposed design change would have to be reviewed and agreed to by the DCA.
(c)
Effectiveness of latest design standards or prior amendment levels. A design standard is intended to address specific hazards. The effectiveness of a specific design standard to address the hazard(s), from minimizing its effects to eliminating the source, will vary with its amendment history. The proposed modification should be evaluated for its ability to comply fully with the requirement, giving consideration also to the effectiveness of the design standard to address the hazard(s). The effectiveness of the design standards at various amendment levels (beginning with that of the existing certification basis) should be estimated, and the safety benefits of complying with various levels should be compared to that achieved by complying with the existing certification basis.
ii) Not Practical. Compliance with the latest design standards may be considered not practical if the applicant can substantiate that it would result in additional resource requirements (incremental costs) that are not commensurate with the safety benefits to be gained. The incremental costs are those that would be incurred beyond the basic costs of demonstrating compliance with the existing certification basis, and could include additional design changes to the proposed modification required for compliance and the effort required to demonstrate such compliance. Substantiating data and analyses should support an applicant’s position that compliance is not practical, and the ACD should agree with this position.
3) The conclusion of the process in this step should be documented by the ACD, including all the substantiating data submitted by the applicant. Examples of possible conclusion for each affected area would include, but not be limited to:
i) Compliance with the latest requirement is necessary. The applicant would pursue the affected area at the latest amendment level.
ii) Compliance with an amendment level between the existing certification basis and the latest design standard would adequately address the hazard at an acceptable cost. Complying with the latest amendment level would not be practical. The applicant would then propose the intermediate amendment level of the requirement.
iii) The increased level of safety is not commensurate with the increased costs associated with meeting the latest amendment instead of the existing certification basis. Therefore, the applicant would propose the existing certification basis.
iv) The results of the assessment were inconclusive. Further discussions with the applicant are warranted.
g) The Certification Basis of the proposed modification is finalized. The certification basis of the proposed modification can now be finalized, and may consists of a combination of the latest design standards, the design standard of the existing certification basis, or an intermediate level between the existing and the latest design standards. Areas of the aircraft, engine or propeller that are considered unchanged or not affected by the proposed modification can continue to comply with the existing certification basis (i.e. there is no need to re-visit the certification basis).
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