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.
Appendix A A-11 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
21. Comprehensive flightdeck upgrade, such as conversion from entirely federated, independent electro-mechanical flight instruments to highly integrated and combined electronic display systems with extensive use of software and/or complex electronic hardware.
No No Yes Affects avionics and electrical systems integration and architecture concepts and philosophies.
This drives a reassessment of the human-machine interface, flightcrew workload, and re-evaluation of the original design flightdeck assumptions.
22. Introduction of autoland. No No Yes Invalidates original design assumptions.
23. Conversion from a safe life design to a damagetolerance-based design.
No No Yes Where the airframeestablished safe life limits change to damage tolerance principles, then use of an inspection program in lieu of the safe life design limit invalidates the original assumptions used during certification.
Appendix A A-12 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
24. Extensive structural airframe modification, such as a large opening in the fuselage.
Yes No No Requires extensive changes to fuselage structure, affects aircraft systems, and requires a new AFM to address performance and flight characteristics.
25. Fuselage stretch or shortening in the cabin or pressure vessel.
Yes No Yes Cabin interior changes are related changes since occupant safety considerations are impacted by a cabin length change.
Even if a new cabin interior is not included in the product level change, the functional effect of the fuselage plug has implications on occupant safety (e.g., the dynamic environment in an emergency landing, emergency evacuation, etc.), and thus the cabin interior becomes an affected area.