Page 73 - UK Regulation Part 21 Initial Airworthiness Annex I (consolidated) March 2022

PART 21 - INITIAL AIRWORTHINESS (ANNEX I)

and have been found to comply with the earlier Amendment 25-11 of §
25.1141. The existing fleet has achieved approximately (#) flights during which
service experience of the existing design has been found to be acceptable. If
one assumes a complete APU cycle, i.e. start-up and shutdown for each
flight, the number of APU fuel shut-off valve operations would be over 108
cycles, which demonstrates that the valve successfully meets its intended
function and complies with the intent of the certification specification.
F.3.2.4 The applicant provides a description of the design feature and its intended
function. The fuel shut-off valve, actuator design, and operation is essentially
unchanged with the system design ensuring that the valve is monitored for
proper cycling from closed to open at start. If the valve is not in the
appropriate position (i.e. closed), then the APU start is terminated, an
indication is displayed on the flight deck, and any further APU starts are
prevented. Design improvements using the capability of the APU electronic
control unit (ECU) have been incorporated in this proposed product change.
These design changes ensure that the fuel valve indication system will
indicate failure of proper valve operation to the flight crew, and these features
increase the level of functionality and safety, but the system does not indicate
valve position as required by § 25.1141(f).
F.3.2.5 The FAA and the applicant record this in an issue paper. The FAA can use the
G-1 or a technical issue paper for this purpose. An issue paper was
coordinated, included data, or referenced reports documenting relevant
service experience compiled from incident reports, fleet flight hour/cycle data,
and maintenance records. The issue paper also discussed existing and
proposed design details, failure modes, and analyses showing to what extent
the proposed aeroplane complies with the latest amendment of § 25.1141.
Information is presented to support the applicant’s argument that compliance
with the latest amendment would not materially increase the level of safety.
Comparative data pertaining to aircraft of similar design and construction are
also presented.
F.3.2.6 The conclusion, drawing together the data and rationale, is documented in the
G-1 issue paper. The additional features incorporated in the APU fuel shut-off
valve will provide a significant increase in safety to an existing design with
satisfactory service experience. The applicant proposes that compliance with
the latest amendment would not materially increase the level of safety and
that compliance with § 25.1141 at Amendment 25-11 would provide an
acceptable level of safety for the proposed product change.
21.A.101 APPG to GM Appendix G to GM 21.A.101 Changed product rule (CPR) decision record

21.A.101 APPH to GM Appendix H to GM 21.A.101 Examples of documenting the proposed certification basis list
H.1 Example 1.
H.1.1 This optional tool may be used to establish the applicable airworthiness and OSD
certification specifications that will become part of the type-certification basis for
airworthiness or OSD certification basis. For a significant change, the applicant
must demonstrate compliance for the change and the area affected by the change
with the certification specifications that were in effect at the date of application.
However, in some cases earlier or later certification specifications can be used, as
allowed in point 21.A.101.
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