Appendix A A-25 A.2 Examples of Substantial, Significant, and Not Significant Changes for Transport Airplanes (Part 25).
A.2.1 Table A-4 contains examples of changes that are “substantial” for transport airplanes (part 25).
Table A-4. Examples of Substantial Changes for Transport Airplanes (Part 25) Example Description of change Notes
1. Change in the number or location of engines, e.g., four to two wing-mounted engines or two wing-mounted to two body-mounted engines.
Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
2. Change from a high-wing to low-wing configuration. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
3. Change from an all-metal to all-composite airplane. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
4. Change of empennage configuration for larger airplanes (cruciform vs. ‘T’ or ‘V’ tail).
Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
5. Increase from subsonic to supersonic flight regime. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Appendix A A-26 A.2.2 Table A-5 contains examples of changes that are “significant” for transport airplanes (part 25).
Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) 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. Reduction in the number of flightcrew (in conjunction with flightdeck update).
No No Yes Extensive changes to avionics and aircraft systems. Impact to crew workload and human factors, pilot type rating.
2. Modify an airplane to add certification for flight in icing conditions by adding systems such as ice detection and ice protection.
Yes No Yes New aircraft operating envelope. Requires major new systems installation and aircraft evaluation. Operating envelope changed.
3. Conversion—passenger or combination freighter/passenger to all freighter, including cargo door, redesign floor structure and 9g net or rigid barrier.
Yes No Yes Extensive airframe changes affecting load paths, aeroelastic characteristics, aircraft related systems for fire protection, etc. Design assumptions changed from passenger to freighter.
Appendix A A-27 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
4. Conversion from a cargo to passenger configuration.
Yes No Yes Completely new floor loading and design. Redistribution of internal loads, change in cabin safety requirements, system changes.
5. Increase in cabin pressurization greater 10 percent.
than No No Yes A change greater than 10 percent in operational cabin pressure differential is a significant change since it requires extensive airframe changes affecting load paths, fatigue evaluation, or aeroelastic characteristics, invalidating the certification assumptions.
6. Addition of leading slats.
edge Yes No Yes The addition of leading edge slats is significant since it requires extensive changes to wing structure, adds aircraft systems, and requires a new AFM to address performance and flight characteristics.
Appendix A A-28 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
7. 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.
8. Extensive structural airframe modification, such as installation of a large telescope with large opening in the fuselage.
Yes No No These types of structural modifications are significant since they require extensive changes to fuselage structure, affect aircraft systems, and require a new AFM to address performance and flight characteristics.
Appendix A A-29 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
9. Changing the number of axles or number of landing gear done in context with a product change that involves changing the airplane gross weight.
Yes No No This type of landing gear change with an increase in gross weight is significant since it requires changes to aircraft structure, affects aircraft systems, and requires AFM changes, which invalidate the certification assumptions.
10. Primary structure changes from metallic material to composite material.
No Yes No Change in principles of construction and design from conventional practices.
11. An increase in design weight of more than 10 percent.
No No Yes Design weight increases of more than 10 percent result in significant design load increase that invalidates the assumptions used for certification, requiring re-substantiation of aircraft structure, aircraft performance, and flying qualities and associated systems.
Appendix A A-30 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
12. Installation of winglets, modification of existing winglets, or other changes in wing tip design.
Yes No Yes Significant if it requires extensive changes to wing structure or aircraft systems, or if it requires a new AFM to address performance and flight characteristics. It may also affect the wing fuel tanks, including fuel tank lightning protection, fuel tank ignition source prevention, and fuel tank flammability exposure.
13. Changes in wing span, chord, or sweep.
Yes No Yes Significant if it requires extensive changes to wing structure or aircraft systems, or if it requires a new AFM to address performance and flight characteristics. It may also affect the wing fuel tanks, including fuel tank lightning protection, fuel tank ignition source prevention, and fuel tank flammability exposure.
Appendix A A-31 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
14. A change in the type or number of emergency exits or an increase in the maximum certificated number of passengers.
Yes No Yes
15. A comprehensive avionics upgrade that changes a federated avionics system to a highly integrated avionics system.
No No Yes This change refers to the avionics system that feeds the output to displays and not the displays themselves.
16. An avionics upgrade that changes the method of input from the flightcrew, which was not contemplated during the original certification.
No No Yes A change that includes touchscreen technology typically does not invalidate the assumptions used for certification. A change that incorporates voice activated controls or other novel human-machine interface would likely invalidate the assumptions used for certification.
Appendix A A-32 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
17. Change in primary flight controls to FBW system.
(Some airplanes have some degree of FBW.
Achieving full FBW may be a not significant change on some airplanes.)
No No Yes When the degree of change is so extensive that it affects basic aircraft systems integration and architecture concepts and philosophies.
This drives a complete reassessment of flightcrew workload, handling qualities, and performance evaluation, which are different from the original design assumptions.
18. Replace reciprocating with 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.
Appendix A A-33 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
19. Maximum continuous or takeoff thrust or power increase of more than 10 percent or, for turbofans, an increase of the nacelle diameter.
No No Yes A thrust or power increase of more than 10 percent is significant because it does have a marked effect on aircraft performance and flying qualities, or requires re-substantiation of powerplant installation. An increase of the nacelle diameter as a result of an increase in the bypass ratio is significant because it results in airframe-level effects on aircraft performance and flying qualities. However, a small increase of the nacelle diameter would not have such an airframe-level effect and would not be considered a significant change.
Appendix A A-34 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
20. Initial installation of an autoland system.
No No Yes Baseline airplane not designed for autoland operation, potential crew workload, and systems compatibility issues.
21. Installation of a new fuel tank, e.g., installation of an auxiliary fuel tank in a cargo bay or installation of an auxiliary fuel tank that converts a dry bay into a fuel tank (such as a horizontal stabilizer tank).
No No Yes Requires changes to airframe, systems, and AFM. Results in performance changes. These changes typically affect fuel tank lightning protection, fuel tank ignition source prevention, and fuel tank flammability exposure.
22. Main deck cargo door installation.
Yes No No Redistribution of internal loads, change in aeroelastic characteristics, system changes.
Appendix A A-35 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
23. 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).
24. Changing the floor from passenger carrying to cargo carrying capability.
Yes No Yes Completely new floor loading and design. Redistribution of internal loads, change in cabin safety requirements, system changes. If a cargo handling system is installed, it would be a related change.
25. Initial installation of an APU essential for aircraft flight operation.
No No Yes Changes emergency electrical power requirements, change in flight manual and operating characteristics.
Appendix A A-36 Table A-5. Examples of Significant Changes for Transport Airplanes (Part 25) (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
26. Conversion from hydraulically actuated brakes to electrically actuated brakes.
No No Yes Assumptions of certification for airplane performance are changed.
27. Installation of engine thrust reversers.
Yes No Yes
28. Request for extended operations (ETOPS) type design approval for:
(a) airplanes without an existing ETOPS type design approval, and
(b) extension of an airplane’s diversion time.
No No Yes An expansion of diversion capability for ETOPS would normally be a significant change. However, expanding the diversion capability for which it was originally designed is generally not a significant change. In this case, the assumptions used for certification of the basic product remain valid, and the results can be applied to cover the changed product with predictable effects or can be demonstrated without significant physical changes to the product.