Avionics News February 2013 - 19
FREQUENTLY ASKED QUESTIONS
Type Design Approval
Can you elaborate on the use of extended model list in
case of minor changes for common replacements (box out
– box in) of basic avionics equipment (e.g. transponder)?
The following information is found on the European Aviation
Safety Agency’s frequently asked questions website.
“The replacement of avionics is a change to the
type design that has to be approved in accordance with Part 21, and, for that, it has to be
classified as major or minor, depending on the
effect that the change has on the airworthiness
of the AC. The rules for the classification are
identified in paragraph 21.A.91 and the guidance in the GM 21.A.91. Additional guidance
can be found in the FAA AC 23.1309-1E and
the FAQ table of design change classification.
Regarding the applicability of the change, each
application needs to include a reference to
the TC and the eligible AC type/model to be
changed. As indicated on the EASA website at
the FAQ for fees and charges, one application
for TC, RTC, STC, major and minor change
can cover several models but not more than one
type per certificate.
There are, however, some exceptions where a
list of models, applicable to aircraft covered
by different TCs, has been accepted. In such
case, it has to be shown that the design change
and the demonstration of compliance are valid,
without relevant differences, on all the TC’s
models listed in the paragraph on the applicability of the modification.
Modifications consisting of a replacement (box
out – box in) of basic avionics (e.g. transponder) represent one such exception. In order for
a design change to fall into this category, where
an extended model list of AC from different
types can be accepted, the following criteria
should be met:
• The design change is classified as
minor according to Part 21.A.91.
• A proper and detailed model list is
• A common certification basis in the
area of the change can be applied.
• Commuter category is excluded.
• The design change must be a pure
replacement (box out - box in).
• For equipment located on the
flight deck, it must be replaced by
equipment that utilizes the same
location as the equipment that was
• The validity of the modification
design has been checked and justified
in writing for all the models in the list.
• The minor classification is valid for
all the models on the list. This means
that the conditions that make the
classification minor are valid for all
the models (and categories), and no
limitation is invalidated. For example,
installation of transponder on AC with
cruise TAS greater than 250 knots is
The following conditions also apply:
• The mass of the new equipment is not
• Cables and antennas have not changed
(change of the mating electrical
connector on the aircraft is accepted).
• The equipment does not add any new
Meeting all the above conditions typically
allows acceptance of applications with extended
model list. When one or more of the above conditions are not met, a case-by-case evaluation is
possible. In both cases, acceptance will not constitute a precedent for any future change.” q