5-7 change to type design. A separate STC or amended TC may be required to remove modifications and the resulting certification basis established for the changed product.
5.12 The Certification Basis is Part of the Design Change.
A new design change may be installed in a product in production or via a service bulletin or STC. In terms of § 21.101, each of the approved design changes has its own basis of certification. If an applicant chooses to remove an approved installation
(e.g., interior installation, avionics equipment) and install a new installation, a new certification basis may be required for the new installation, depending on whether the change associated with the new installation is considered significant compared to the baseline configuration that the applicant chooses. If the new installation is a not significant change, the unmodified product’s certification basis may be used (not the previous installation certification basis), provided the certification basis is adequate. For example, a transport category airplane is certified as a “green” configuration. The airplane certification basis does not include § 25.562 if it was manufactured prior to October 28, 2009. An interior is installed under an STC, and the applicant elects to include § 25.562 (dynamic seats) in the certification basis to meet specific operational requirements. At a later date, the airplane is sold to a non-part 121 operator (i.e., does not have the same operating requirements). A new interior is installed; there will be no requirement for § 25.562 to be included in the new certification basis.
5.13 Sequential Design Changes—Cumulative Effects.
5.13.1 If you intend to accomplish a product change by incorporating several design changes in a sequential manner, you should identify to the FAA up front when the first application is made. In addition, the cumulative effects arising from the initial change, and from all of the follow-on changes should be included as part of the description of the change in the initial proposal. The classification of the intended product change will not be evaluated solely on the basis of the first application, but rather on the basis of all the required design changes needed to accomplish the intended product change. If the FAA determines that the current application is a part of a sequence of related changes, then the FAA will re-evaluate the determination of significance and the resulting certification basis as a group of related changes.
5.13.2 Example: Cumulative Effects—Advancing the Certification Basis.
The type certificate for airplane model X lists three models, namely X-300, X-200, and X-100. The X-300 is derived from the X-200, which is derived from the original X-100 model. An applicant proposes a design change to the X-300 airplane model. During the review of the X-300 certification basis and the regulations affected by the proposed change, it was identified that one regulation, § 25.571 (damage tolerance requirements), remained at the same amendment level as the X-100 original certification basis (exception granted on the X-200). Since the amendment level for this particular regulation was not changed for the two subsequent airplane models (X-200 and X-300), the applicant must now examine the cumulative effects of these two previous design
5-8 changes that are related to the proposed change and the damage tolerance requirements to determine whether the amendment level needs to advance.
Appendix A A-1 APPENDIX A. CLASSIFICATION OF DESIGN CHANGES The following tables of “substantial,” “significant,” and “not significant” changes are adopted by the FAA, Agência Nacional de Aviação Civil (ANAC), European Aviation Safety Agency (EASA), and Transport Canada Civil Aviation (TCCA) through international collaboration. The classification may change due to cumulative effects and/or combinations of individual changes.
A.1 Examples of Substantial, Significant, and Not Significant Changes for Small Airplanes (Part 23).
A.1.1 Table A-1 contains examples of changes that are “substantial” for small airplanes (part 23).
Table A-1. Examples of Substantial Changes for Small Airplanes (Part 23) Example Description of Change Notes
1. Change in wing location (tandem, forward, canard, high/low).
Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
2. Fixed wing to tilt wing. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
3. A change in the number of engines. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
4. Replacement of piston or turbo-prop engines with turbojet or turbofan engines.
Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Appendix A A-2 Table A-1. Examples of Substantial Changes for Small Airplanes (Part 23) (continued) Example Description of Change Notes
5. Change in engine configuration (tractor/pusher). Proposed change in design is so extensive that a substantially complete investigation of compliance applicable regulations is required.
with the
6. Increase from subsonic to supersonic flight regime.
7. Change from an all-metal to all-composite airplane. Proposed change in design is so extensive that a substantially complete investigation of compliance applicable regulations is required.
with the
8. Certificating a part 23 (or predecessor amendment airplane basis airplane such as CAR 3) into another regulatory category such as part 25.
Appendix A A-3 A.1.2 Table A-2 contains examples of changes that are “significant” for small airplanes (part 23).
Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
1. Conventional tail to T-tail or V-tail, or vice versa.
Yes No Yes Change in general configuration. Requires extensive, structural flying qualities and performance reinvestigation. Requires new airplane flight manual (AFM) to address performance and flight characteristics.
2. Changes in wing configuration such as change in dihedral, changes in wing span, flap or aileron span, addition of winglets, or increase of more than 10 percent of the original wing sweep at the quarter chord.
Yes No Yes Change in general configuration. Likely requires extensive changes to wing structure. Requires new AFM to address performance and flight characteristics.
Note: Small changes to the wingtip or winglet are not significant changes. See table for “not significant” changes.
Appendix A A-4 Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) (continued) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
3. Changes to tail configuration such as the addition of tail strakes or angle of incidence of the tail.
Yes No Yes Change in general configuration. Likely requires extensive changes to tail structure. Requires new AFM to address performance and flight characteristics.
Note: Small changes to tail are not significant changes.
4. Tricycle/tail wheel undercarriage change or addition of floats.
Yes No No Change in general configuration. Likely, at airplane level, general configuration and certification assumptions remain valid.
5. Passenger to freighter configuration conversion that involves the introduction of a cargo door or an increase in floor loading of more than 20 percent, or provision for carriage of passengers and freight together.
Yes No Yes Change in general configuration affecting load paths, aeroelastic characteristics, aircraft related systems, etc. Change in design assumptions.
Appendix A A-5 Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) (continued) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
6. Replace reciprocating engines with the same number of turbo-propeller engines.
Yes No No Requires extensive changes to airframe structure, addition of aircraft systems, and new AFM to address performance and flight characteristics.
7. Addition of a turbo-charger that changes the power envelope, operating range, or limitations.
No No Yes Invalidates certification assumptions due to changes in operating envelope and limitations. Requires new AFM to address performance and flight characteristics.
Appendix A A-6 Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) (continued) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
8. The replacement of an engine of higher rated power or increase thrust would be considered significant if it would invalidate the existing substantiation, or would change the primary structure, aerodynamics, or operating envelope sufficiently to invalidate the assumptions of certification.
No Yes Yes Invalidates certification assumptions. Requires new AFM to address performance and flight characteristics.
Likely changes to primary structure. Requires extensive construction reinvestigation.
9. A change in the type of material, such as composites in place of metal, or one composite fiber material system with another (e.g., carbon for fiberglass), for primary structure would normally be assessed as a significant change.
No Yes Yes Change in principles of construction and design from conventional practices. Likely change in design/certification assumptions.
Appendix A A-7 Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) (continued) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
10. A change involving appreciable increase in design speeds VD, VB, VMO, VC, or VA.
No No Yes Certification assumptions invalidated. Requires new AFM to address performance and flight characteristics.
11. Installation of a short takeoff and landing (STOL) kit.
No No Yes Certification assumptions invalidated. Requires new AFM to address performance and flight characteristics.
12. A change in the rated power or thrust could be a significant change if the applicant is taking credit for increased design speeds per example 10 of this table.
No No Yes Certification assumptions invalidated. Requires new AFM to address performance and flight characteristics.
Appendix A A-8 Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) (continued) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
13. Fuel state such as compressed gaseous fuels or fuel cells. This could completely alter the fuel storage and handling systems and possibly affect the airplane structure.
No No Yes Changes in design/certification assumptions. Extensive alteration of fuel storage and handling systems.
14. A change in the flight control concept for an aircraft, e.g., to fly by wire (FBW) and side-stick control, or a change from hydraulic to electronically actuated flight controls, would in isolation normally be regarded as a significant change.
No No Yes Changes in design and certification assumptions.
Requires extensive systems architecture and integration reinvestigation. Requires new AFM.
Appendix A A-9 Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) (continued) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
15. Change to airplane’s operating altitude, or cabin operating pressure greater than 10 percent in maximum cabin pressure differential.
No No Yes This typically invalidates certification assumptions and the fundamental approach used in decompression, structural strength, and fatigue. May require extensive airframe changes affecting load paths, fatigue evaluation, aeroelastic characteristics, etc.
Invalidates design assumptions.
16. Addition of cabin pressurization system.
No Yes Yes Extensive airframe changes affecting load paths, fatigue evaluation, aeroelastic characteristics, etc.
Invalidates design assumptions.
17. Changes in types and number of emergency exits or an increase in maximum certificated passenger capacity.
Yes No Yes Emergency egress requirements exceed those previously substantiated.
Invalidates assumptions of certification.
Appendix A A-10 Table A-2. Examples of Significant Changes for Small Airplanes (Part 23) (continued) Example Description of change Is there a change to the general configuration?
§ 21.101(b)(1)(i) Is there a change to the principles of construction?
§ 21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
§ 21.101(b)(1)(ii) Notes
18. A change in the required number of flightcrew that necessitates a complete flightdeck rearrangement, and/or an increase in pilot workload.
No No Yes Extensive changes to avionics and aircraft systems.
Invalidates certification assumptions. Requires new AFM.
19. Expansion of an aircraft’s operating envelope.* No No Yes* *Some changes may be deemed “not significant” depending on the extent of the expansion.
An expansion of operating capability is a significant change (e.g., an increase in maximum altitude limitation, approval for flight in icing conditions, or an increase in airspeed limitations).
20. Replacement of an aviation gasoline engine with an engine of approximately the same horsepower utilizing, e.g., diesel, hybrid, or electrical power.
No No Yes A major change to the airplane. The general configuration and principles of construction will usually remain valid; however, the assumptions for certification are invalidated.