Page 64 - UK Regulation Part 21 Initial Airworthiness Annex I (consolidated) March 2022

PART 21 - INITIAL AIRWORTHINESS (ANNEX I)

21.A.101 APPC to GM Appendix C to GM 21.A.101 A method to determine the changed and affected areas
C.1 Overview.
C.1.1 When a product is changed, some areas may change physically, while others may
change functionally. The CAA refers to this combination as changed and affected
areas. For example, an extension to the wing of a fixed-wing aircraft would
physically change the wing tip and likely other wing structure. Some areas of the
airframe may have sufficient strength for the increase in load and would change
functionally, i.e. they would carry greater load, but they would not change physically.
These areas have associated certification specifications, which become part of the
certification basis for the change.
C.1.2 Figure C-1 below provides an overview of one method that applicants may use to
determine the changed and affected areas and the applicable certification
specifications.
C.2 Physical Changes.
C.2.1 Steps.
- Step 1. Make a list of the physical changes.
- Step 2. List the corresponding certification specifications applicable to the
physical changes.
- Step 3. List the amendment level recorded on the existing certification basis
of the baseline product and the amendments on the date of application.
C.2.2 Example.
The change is adding a winglet to a fixedwing aircraft and a change to the leadingedge
slats for a performance increase. As part of the change, an electrically driven slat actuator
is modified by changing the mounting structure of the actuator used to connect the
actuator to the slat. The actuator structure is changed. The electrical system in the
actuator is not affected. The applicant would list certification specifications applicable to
the actuator. The applicant would not list the certification specifications applicable to the
electrical system of the actuator. See Table C1 below for an example of how to chart a
physical change and the associated certification specifications.
C.3 Functional Changes.
C.3.1 Steps.
- Step 1. Describe each change.
- Step 2. Describe the effects of the change (e.g. structural, performance,
electrical, etc.).
- Step 3. List the areas, systems, parts, and appliances that are affected by
those effects.
- Step 4. List the certification specifications associated with the effects for each
area, system, part, or appliance.
- Step 5. List the amendment level recorded on the existing certification basis
of the baseline product and the amendments on the date of application.
C.3.2 Example.
The change is adding a winglet to a fixedwing aircraft and a change to the leadingedge
slats for a performance increase. The wing root bending moment has increased. The
loads in the wing box are increased but the wing box has sufficient structural margins to
carry the higher loads. Thus, the wing box is not physically changed but its function has
changed because it carries greater loads. See Table C2 below for an example of how to
chart a functional change, its effects, and the affected areas (steps 1 through 3 above).
See Table C3 below for an example of how to chart an area affected by a functional
change and the associated certification specifications (steps 4 and 5 above).
C.4 Combine the Lists.
C.4.1 the CAA typically presents the certification basis for a product by certification
specification and not by area. The next step is to combine these two lists. However,
since only a portion of the product is being changed, the changed and affected
areas of the new certification basis need to be identified. The unchanged area is not
required to comply with the certification specifications in effect at the date of
application. (See point 21.A.101(b)(2))
C.4.2 When the change is quite extensive, applicants will save time by listing all the
certification specifications applicable to the category of product they are certifying.
They can use Table C-4 below in the next step where they will identify any other
exceptions that they would like the CAA to consider.
C.4.3 Example. If we use the examples above for the combined list for the actuator
structural changes and the wing box functional change, then the certification basis
would be listed as shown in Table C-4 below.
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