Appendix A A-64 A.4 Examples of Substantial, Significant, and Not Significant Changes for Engines (Parts 33) A.4.1 Table A-10 contains examples of changes that are “substantial” for engines (part 33).
Table A-10. Examples of Substantial Changes for Engines (Part 33) Example Description of Change Notes Turbine Engines
1. Traditional turbofan to geared-fan engine. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
2. Low bypass ratio engine to high bypass ratio engine with an increased inlet area.
Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
3. Turbojet to turbofan. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
4. Turbo-shaft to turbo-propeller. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
5. Conventional ducted fan to unducted fan. Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
6. Turbine engine for subsonic operation to afterburning engine for supersonic operation.
Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Appendix A A-65 A.4.2 Table A-11 contains examples of changes that are “significant” for engines (part 33).
Table A-11. Examples of Significant Changes for Engines (Part 33) 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 Turbine Engines
1. Increase/decrease in the number of compressor/turbine stages with resultant change in approved operational limitations.
Yes No Yes Change is associated with other changes that would affect the rating of the engine and the engine dynamic behavior, such as backbone bending, torque spike effects on rotors and casing, surge and stall characteristics, etc.
Appendix A A-66 Table A-11. Examples of Significant Changes for Engines (Part 33) (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 Turbine Engines
2. New design fan blade and fan hub, or a bladed fan disk to a blisk, or a fan diameter change, that could not be retrofitted.
Yes No Yes Change is associated with other changes to the engine thrust/power, ratings, and operating limitations; engine dynamic behavior in terms of backbone bending, torque spike effects on casing, foreign object ingestion behavior (birds, hail, rain, ice slab); blade-out test and containment; induction system icing capabilities; and burst model protection for the aircraft. If there is a diameter change, installation will be also affected.
3. Hydro-mechanical control to FADEC/EEC (electronic engine control) without hydro-mechanical backup.
Yes No No Change in engine control configuration.
Not interchangeable.
Likely fundamental change to engine operation.
Appendix A A-67 Table A-11. Examples of Significant Changes for Engines (Part 33) (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 Turbine Engines
4. A change in the containment case from hard-wall to composite construction or vice versa that could not be retrofitted without additional major changes to the engine or restricting the initial limitations or restrictions in the initial installation manual.
No Yes Yes Change in methods of construction that have affected inherent strength, backbone bending, blade to case clearance retention, containment wave effect on installation, effect on burst model, torque spike effects.
Appendix A A-68 Table A-11. Examples of Significant Changes for Engines (Part 33) (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 Turbine Engines
5. A change to the gas generator (core, turbine/compressor/ combustor) in conjunction with changes in approved operating limitations.
No No Yes Change is associated with other changes that would affect engine thrust/power and operating limitations, and have affected the dynamic behavior of the engine, foreign object ingestion behavior (birds, hail storm, rain, ice shed), induction system icing capabilities.
Assumptions used for certification may no longer be valid.
6. A change from traditional metal to composite materials on an assembly or structure that provides a load path for the engine affecting the engine dynamic behavior and/or the engine inherent strength.
No Yes Yes Change in principles of construction and design.
Appendix A A-69 Table A-11. Examples of Significant Changes for Engines (Part 33) (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 Piston Engines
7. Convert from mechanical to electronic control system.
Yes Yes No Change in engine configuration: installation interface of engine changed.
Changes to principles of construction: digital controllers and sensors require new construction techniques and environmental testing.
8. Add turbocharger that increases performance and changes in overall product.
Yes No Yes Change in general configuration: installation interface of engine changed (exhaust system).
Certification assumptions invalidated: change in operating envelope and performance.
Appendix A A-70 Table A-11. Examples of Significant Changes for Engines (Part 33) (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 Piston Engines
9. Convert from air-cooled cylinders to liquid cooled cylinders.
Yes No Yes Change to general configuration: installation interface of engine changed (cooling lines from radiator, change to cooling baffles).
Certification assumptions invalidated: change in operating envelope and engine temperature requirements.
10. A change from traditional metal to composite materials on an assembly or structure that provides a load path for the engine affecting the engine dynamic behavior and/or the engine inherent strength.
No Yes Yes Change in principles of construction and design.
Appendix A A-71 Table A-11. Examples of Significant Changes for Engines (Part 33) (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 Piston Engines
11. Convert from spark-ignition to compression-ignition.
Yes No Yes Change in general configuration: installation interface of engine changed (no mixture lever).
Certification assumptions invalidated: change in operating envelope and performance.
Appendix A A-72 A.4.3 Table A-12 contains examples of changes that are “not significant” for engines (part 33).
Table A-12. Examples of Not Significant Changes for Engines (Part 33) 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 Turbine Engines
1. Change in the material from one type of metal to another type of metal of a compressor drum.
No No No No change in performance.
Assumptions are still valid.
2. Increase/decrease in the number of compressor/turbine stages without resultant change in operational performance envelope.
No No No No change in performance.
Assumptions are still valid.
Appendix A A-73 Table A-12. Examples of Not Significant Changes for Engines (Part 33) (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 Turbine Engines
3. Hardware design changes to the FADEC/EEC, the introduction of which do not change the function of the system.
No No No No change in configuration.
Retrofitable.
Assumptions used for certification are still valid.
Possible changes in principles of construction are insignificant.
4. Software changes. No No No
5. Rub-strip design changes. No No No Component level change.
6. A new combustor that does not change the approved limitations or dynamic behavior.* (*Exclude life limits.)
No No No Component level change.
7. Bearing changes. No No No Component level change.
Appendix A A-74 Table A-12. Examples of Not Significant Changes for Engines (Part 33) (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 Turbine Engines
8. New blade designs with similar material that can be retrofitted.
No No No Component level change.
9. Fan blade redesign that can be retrofitted.
No No No Component level change.
10. Oil tank redesign. No No No Component level change.
11. Change from one hydromechanical control to another hydro-mechanical control.
No No No Component level change.
12. Change to limits on life limited components supported by data that became available after certification.
No No No Extending or reducing the life limits. For example, extending life limits based on credits from service experience or new fatigue data.
13. Changes to limits on exhaust gas temperature.
No No No
Appendix A A-75 Table A-12. Examples of Not Significant Changes for Engines (Part 33) (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 Turbine Engines
14. Changes to Airworthiness Limitations section with no configuration changes.
No No No
15. Bump ratings within the product’s physical capabilities that may be enhanced with gas path changes such as blade restaggering, cooling hole patterns, blade coating changes, etc.
No No No