Page 206 - UK Regulation Part 21 Initial Airworthiness Annex I (consolidated) March 2022

PART 21 - INITIAL AIRWORTHINESS (ANNEX I)

For major changes, the complexity of the change should be taken into
account, rather than the complexity of the original system.
Whether or not a CDI is complex should be determined in a conservative
manner if this cannot be determined at an early stage of the certification
project. When greater clarity has been achieved, the complexity may be
reevaluated and the LoI adapted accordingly.
3.2.4 Performance of the design organisation
The assessment of the level of performance of the design organisation takes
into account the applicant’s experience with the applicable certification
processes, including their performance on previous projects and their degree
of familiarity with the applicable certification requirements.
For approved design organisations, the CAA uses relevant data to consider
the design organisation’s expected performance at an organisational, panel or
discipline level, depending on the availability of data ¹.
This data stems from design organisation audits, the applicant’s measured
level of performance on previous projects, and their performance during the
familiarisation phase. the CAA shares this data with the respective design
organisations (in the form of the design organisation approval (DOA)
dashboard).
For each CDI proposed by the applicant, the DOA holder’s performance
associated with the affected disciplines or panels is to be considered.
If one CDI affects more panels or disciplines than the others, a conservative
approach should be followed in selecting the lower performance level. As an
alternative, that CDI may be assessed separately for each affected the CAA
panel or discipline.
If, for a wellestablished organisation, there is no shared performance data
available at the panel level, it may be acceptable to propose the overall DOA
holder’s performance. If the organisation or its scope are fundamentally new,
the ‘unknown’ level of performance should be conservatively proposed by the
applicant.
The determination of the performance of the design organisation may also
take into consideration information that is more specific or more recent than
the information on the DOA holder’s dashboard, e.g. experience gained during
technical familiarisation with the current certification project, the performance
of compliance verification engineers and of the affected technical areas, as
well as the performance of the design organisation in overseeing
subcontractors and suppliers.
The performance of some applicants’ organisations is not known if:
- The the CAA has agreed in accordance with point 21.A.14(b) that the
applicants may use procedures that set out specific design practices,
as an alternative means to demonstrate their capability (excluding
United Kingdom technical standard order (UKTSO) applicants for other
than APU, covered by point 21.B.100(b)); or
- the applicants demonstrate their capability by providing the CAA with the
certification programme in accordance with point 21.A.14(c).
In these cases, the assumed level of performance is ‘unknown’.
Exceptionally, the CAA may consider a higher level of performance for a
specific CDI if that is proposed and properly justified by the applicant.
The following list includes some examples:
- a CDI with which the CAA is fully familiar and satisfied (from previous
similar projects) regarding the demonstration of compliance proposed
by the applicant;
- if the applicant fully delegates the demonstration of compliance to a
supplier that holds a DOA, the performance level of the supplier may be
proposed.
3.2.5 Likelihood of an unidentified non-compliance
Assessing the likelihood of an unidentified noncompliance is the first step that
is necessary to determine the risk class.
The likelihood of an unidentified noncompliance should not be confused with
the likelihood of occurrence of an unsafe condition as per AMC 21.A.3B(b). In
fact, that AMC provides the CAA's confidence level that the design
organisation addresses all the details of the certification basis for the CDI
concerned, and that a non compliance will not occur.
The likelihood of an unidentified noncompliance is established as being in one
of four categories (very low, low, medium, high), depending on the level of
performance of the design organisation as assessed by the CAA, and on
whether the CDI is novel or complex, as follows:
3.3 Criticality
The second step that is necessary to determine the risk class is the assessment of
the potential impact of a noncompliance on part of the certification basis regarding
the airworthiness or the environmental protection of the product. For the purpose of
risk class determination, the following simplification has been made: the impact of a
non compliance can be either critical or noncritical.
Some of the guidance below has been derived from GM 21.A.91, not due to a
major/minor change classification, but because the same considerations may be
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