GM2 to AMC 20-189 — OPR classification

ED Decision 2020/010/R

The following paragraph links the classifications presented in DO-248C/ED-94C, DP #9 to those defined in AMC 20-189, subparagraph 6.1. This paragraph highlights the clarifications made to the former scheme (e.g. removing the overlaps between the classifications).

1.       The most important clarification compared with the former classification scheme is to give each OPR a single classification using a given order of priority as reflected in AMC 20-189 subparagraph 6.1.2. This promotes visibility of the most relevant issues and helps to prevent inconsistencies in classification. For example, a missing or incorrect requirement issue can be classified as ‘Life-cycle data’ only if it is confirmed that it cannot be classified as ‘Significant’, ‘Functional’, or ‘Process’, in that order of priority.

2.       Type ‘Significant’: this typically maps to ‘Type 0’. However, some applicants may have used ‘Type 1A’ to characterise some PRs, for instance, those linked to Major failure conditions. The AMC 20-189 scheme clarifies that those PRs potentially causing or contributing to Catastrophic, Hazardous or Major failure conditions belong to the class ‘Significant’.

3.       Type ‘Functional’: this typically maps to ‘Type 1A’ or ‘Type 1B’, that is, a problem that results in a failure with a minor or no adverse impact on safety. A PR whose consequences are a failure that can potentially lead to a Minor failure condition could be mapped to ‘Type 1A’, and a PR leading to a failure having No Safety Effect could be mapped to ‘Type 1B’. Two separate subclassifications could therefore be created in the applicant’s classification scheme to ease the mapping: problems having a functional effect leading to a Minor failure condition could be classified separately (e.g. ‘Functional 1’) from the ones having No Safety Effect (e.g. ‘Functional 2’). Moreover, an important clarification is that AMC 20-189 does not explicitly consider the ‘operational’ nature of a PR in the classification scheme to avoid creating overlaps, as a PR with operational consequences could either be classified as ‘Significant’ or ‘Functional’. Creating an ‘Operational’ subclassification within the classification ‘Significant’ or ‘Functional’ is nevertheless an option available to stakeholders to create a specific emphasis on operational issues within the proposed classification scheme.

4.       Type ‘Process’: this may map to ‘Type 3A’; however, not in cases where the process non-compliance or deficiency could result in either not detecting a failure or creating a failure. An important clarification in AMC 20-189 is the removal of the ambiguous notion of ‘significant deviation from the plans or standards’ used in the definition of ‘Type 3A’. The ‘Process’ classification in AMC 20-189 should be used for PRs that record a process non-compliance or deficiency, provided they cannot result in a potential safety or potential functional effect. An example of an OPR that should not be classified as a ‘Process’ PR is one related to a requirement that was not completely verified due to a process deficiency, because the potential safety or functional impact remains undetermined. Considering the highest priority classification would, in such a case, lead to a ‘Significant’ or ‘Functional’ classification, thus putting even more emphasis on the need to resolve the shortcoming in the verification activities.

5.       Type ‘Life-cycle data’: this typically maps to ‘Type 2’ or ‘Type 3B’. Since ‘Life-cycle data’ OPRs may range widely, subclassifications may be proposed by stakeholders to distinguish the different types of OPRs. Examples of OPRs classified as ‘Life-cycle data’ may range from issues in a component having no potential safety or functional impact to PRs on pure documentary issues. Moreover, the removal of the notion of ‘non-significant deviation from the plans or standards’ from the definition of ‘Type 3B’ helps to remove the ambiguity and overlap between the ‘Process’ and ‘Life-cycle data’ classifications.

6.       Other OPR classification: additional classifications of OPRs may be created to cover ‘Type 4’ or any other classification not specified in AMC 20-189, paragraph 6.1.1.