09/03/2010 AC21.101A Appendix C C-2
(c) Service bulletins;
(d) Airworthiness directives;
(e) Repairs;
(f) Modifications;
(g) Flight hours/cycles for fl eet leader and total fleet;
(h) World airline accident summary data;
(i) Service difficulty reports;
(j) National Transportation Safety Board reports; and
(k) Warranty, repair and parts usage data.
(2) Show that the data presented represen t all relevant service experience for the product, including the results of any operator surveys, and is comprehensive enough to be representative.
(3) Show that the service experience is relevant to the hazard.
(4) Identification and evaluation of each of th e main areas of concern with regard to:
(a) Recurring and/or common failure modes;
(b) Cause;
(c) Probability, by qualita tive reasoning; and
(d) Measures already taken and their effects.
(5) Relevant data pertaining to aircraft of similar design and construction may be included.
(6) Evaluation of failure modes and conseque nces through analytical processes. The analytical processes should be supported by:
(a) A review of previ ous test results;
(b) Additional detailed testing as required, or
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(c) A review aircraft functional hazard assessments (FHA) and any applicable system safety assessments (SSA) as required.
f. A conclusion that draws together the data and the rationale.
g. These guidelines are not intended to be limiting, either in setting required minimum elements or in precluding alternative forms of submission. Each case may be different, based on the particulars of the system being examined and the requirement to be addressed.
3. Example: 14 CFR § 25.1141(f) Powerplant Controls for Transport Airplanes.
a. The following example, for transport airplanes (14 CFR § 25.1141(f) Auxiliary Power Unit (APU) Fuel Valve Position Indication System), illustrates the typical process an applicant follows. The process will be the same for all product types.
b. This example comes from a derivative model transport airplane where significant changes were made to the main airframe components, engines and systems, and APU. The baseline airplane has an extensive service history. The example shows how the use of service experience supports a finding that compliance with the latest regulation would not contribute materially to the level of safety and that application of the existing certification basis (or earlier amendment) would be appropriate. The example is for significant derivatives of transport airplanes with extensive service history, and illustrates the process, following the guidelines in this appendix, but does not include the level of detail normally required.
(1) Determine the differences between the re gulation in the existing certification basis and the regulation as amended, and the effect of the change in the regulation. The existing certification basis of the airplane that is being changed is the initial release of part 25.
Amendment 25-40 added requirement 14 CFR § 25.1141(f), which mandates that power-assisted valves must have a means to indicate to the flight crew when the valve is in the fully open or closed position, or is moving between these positions. The addressed hazard would be risk of APU fire due to fuel accumulation caused by excessive unsuccessful APU start attempts.
(2) What aspect of the proposed changed pr oduct would not meet the latest regulations?
The proposed APU fuel valve position indication system does not provide the flight crew with fuel valve position or transition indication and, therefore, does not comply with the requirements of 14 CFR § 25.1141(f).
(3) The applicant provides evidence that the proposed certification basis for the changed product, together with applicable service experience of the existing design, provide a level of safety comparable to that intended by the latest regulation. The APU fuel shut-off valve and actuator are unchanged from those used on the current family of airplanes, and have been found to comply with the earlier amendment 25-11 of 14 CFR § 25.1141(f). 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
09/03/2010 AC21.101A Appendix C C-4 cycles, which demonstrates that the valve successfully meets its intended function and complies with the intent of the regulation. In addition, the system design for the changed product incorporates features that increase the level of functionality and safety.
(4) The applicant provides a description of th e 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, but the system does not indicate valve position as required by 14 CFR § 25.1141(f).
(5) The FAA and applicant record this in an issue paper. We 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 that has been 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 airplane complies with the latest amendment of 14 CFR § 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.
(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 14 CFR § 25.1141 at amendment 25-11 would provide an acceptable level of safety for the proposed product change.
09/03/2010 AC21.101A Appendix D D-1 Appendix D. Definitions and Terminology
1. Adequate Certification Basis - The type certification basis for a changed product under 14 CFR § 21.101 is considered adequate when the FAA determines that it provides adequate standards for the design change, i.e. when the certification specifications of the applicable airworthiness code and prescribed special conditions provide an appropriate level of safety for the changed product and do not result in any unsafe design features.
2. Aeronautical product – The terms aeronautical product or product(s) used in this guidance material includes type certificated aircraft, engines, and propellers.
3. Affected area, system, component, part or appliance – any system, component, part, or appliance which is either physically altered by a proposed design change or, even if not altered physically, its functional characteristics are altered due to the effects of the physical change.
4. Certification basis – The applicable airworthiness requirements as established in 14 CFR §§ 21.17 and 21.101, as appropriate; special conditions; equivalent level of safety findings; requirements per 14 CFR § 21.21(b)(2); and exemptions applicable to the product to be certificated.
5. Design Change – A change in the type design of an aeronautical product. In the context of this document the terms “change”, “design change” and “type design change” are synonymous.
6. Earlier requirements – The requirements in effect prior to the date of application for the change, but not prior to the existing certification basis.
7. Existing certification basis – The requirements incorporated by reference in the type certificate of the product to be changed.
8. Latest requirements – The requirements in effect on the date of application for the change.
9. Previous relevant design changes – Previous design changes, the cumulative effect of which could result in a product significantly or substantially different from the original product or model, when considered from the last time the latest regulations were applied.
10. Product level change – A change or combination of changes that makes the product distinct from other models of the product (for example, range, payload, speed, design philosophy).
Product level change is defined at the aircraft, aircraft engine, or propeller level of change.
11. Secondary change – A change is a secondary change if compliance to the latest amendment would not contribute materially to the level of safety and where it is part of and consequential to an overall significant change. A secondary change is a physical change that restores without changing the system, structural capacity, or functionality, but is necessary to support a significant change.
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12. Significant change – A change to the type certificate significant to the extent that it changes one or more of the following: general configuration, principles of construction, or the assumptions used for certification, but not to the extent to be considered a substantial change.
The significance of the change is considered in the context of all previous relevant design changes and all related revisions to the applicable regulations. Not all product level changes are significant.
13. Significant change in an area (for excepted aircraft under 14 CFR § 21.101(c) only) – A change in an area is significant if the general configuration or the principals of construction in that area are not retained, or the assumptions used for certification of that area do not remain valid.
14. Substantial change – A change which is so extensive that a substantially complete investigation of compliance with the applicable regulations is required, and consequently a new type certificate, in accordance with 14 CFR § 21.19.
09/03/2010 AC21.101A Appendix E E-1
Appendix E. Related Code of Federal Regulations Sections
1. Related Code of Federal Regulations Paragraphs.
14 CFR § 21.16, Special conditions.
14 CFR § 21.17, Designation of applicable regulations.
14 CFR § 21.19, Changes requiring a new type certificate.
14 CFR § 21.21, Issue of type certificate: normal, utility, acrobatic, commuter, and transport category aircraft; manned free balloons; special classes of aircraft; aircraft engines; propellers.
14 CFR § 21.93, Classification of changes in type design.
14 CFR § 21.101, Designation of applicable regulations.
14 CFR § 21.115, Applicable requirements.
2. How to Get Publications.
Order copies of 14 CFR, parts from the Superintendent of Documents, Government Printing Office, P.O. 979050, St. Louis, MO 63197. For general information telephone (202) 512-1800 or fax (202) 512-2250. You can order copies online at www.access.gpo.gov. Select “Access” then “Online Bookstore.” Select “Aviation,” then “Code of Federal Regulations.”
Order copies of FAA advisory circulars from the U.S. Department of Transportation, Subsequent Distribution Office, M-30, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785. You can also get copies from our FAA website at http://www.airweb.faa.gov/.