Appendix A A-45 The following are examples of SUBSTANTIAL changes for Engines (Parts 33 ) Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Turbo-shaft to turbopropeller NA NA NA Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Note: There may be certain circumstances where this change would be significant.
Conventional ducted fan to unducted fan
NA NA NA Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Turbine engine for subsonic operation to afterburning engine for supersonic operation
NA NA NA Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Appendix A A-46
The following are examples of SIGNIFICANT changes for Engines (Parts 33 ) Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Increase/decrease in the number of compressor/turbine stages with resultant change in approved operational limitations* (* exclude life limits) Yes No Yes Change is associated with other changes to the ratings and operating limitations;
engine dynamic behavior, in terms of backbone bending, torque spike effects on casing, surge and stall characteristics, etc.
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, ratings, and operating limitations; engine dynamic behavior in terms of backbone bending; torque spike effects on casing;
foreign object ingestion behavior; blade-out test and containment; burst model protection for the aircraft. If there is a diameter change, installation will be also affected.
Hydro-mechanical control to electronic engine controls (FADEC/EEC) without hydro mechanical backup Yes No No Change in engine control configuration.
Not interchangeable.
Likely fundamental change to engine operation.
Appendix A A-47 The following are examples of SIGNIFICANT changes for Engines (Parts 33 ) Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes 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 No 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.
Replace gas generator (core, turbine/ compressor/combustor) with a different one associated with changes in approved operational limitations* (*exclude life limits) No No Yes Change is associated with other changes that would affect engine thrust/power and have affected the dynamic behavior of the engine. Assumptions used for certification may no longer be valid.
Piston Engines 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.
Appendix A A-48 The following are examples of SIGNIFICANT changes for Engines (Parts 33 ) Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes 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.
Convert from aircooled 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.
Convert from sparkignition to compressionignition 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-49
The following are examples of NOT SIGNIFICANT changes for Engines (Parts 33 ):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Turbine Engines 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.
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.
New components internal to the electronic engine controls (FADEC/EEC) the introduction of which does 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.
Software changes No No No Rub-strip design changes No No No A new combustor that does not change the approved limitations, or dynamic behavior* (*exclude life limits) No No No Bearing changes No No No New blade designs with similar material that can be retrofitted No No No Fan blade redesign that can be retrofitted No No No
Appendix A A-50 The following are examples of NOT SIGNIFICANT changes for Engines (Parts 33 ):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Oil tank redesign No No No Change from one hydro-mechanical control to another hydro-mechanical control No No No Change to limits on life limited components No No No Changes to limits on exhaust gas temperature No No No Changes in certification maintenance requirements (CMR) with no configuration changes No No No Bump ratings within the product’s physical capabilities that may be enhanced with gas path changes such as blade restaggered, cooling hole patterns, blade coating changes, etc No No No
Appendix A A-51 The following are examples of NOT SIGNIFICANT changes for Engines (Parts 33 ):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes A change in principal physical properties and mechanics of load transfer of a material of primary structure or highly loaded components. For example, change from traditional metal to either an exotic alloy or a composite material on a highly loaded component.
No No No Piston Engine A change in principal physical properties and mechanics of load transfer of a material of primary structure or highly loaded components. For example, change from traditional metal to either an exotic alloy or a composite material on a highly loaded component.
No No No New or redesigned cylinder head, or valves, or pistons No No No Changes in crankshaft No No No Changes in crankcase No No No Changes in carburetor No No No
Appendix A A-52 The following are examples of NOT SIGNIFICANT changes for Engines (Parts 33 ):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Changes in mechanical fuel injection system No No No Changes in mechanical fuel injection pump No No No Engine model change to accommodate new airplane installation.
No change in principles of operation of major subsystems; no significant expansion in power or operating envelopes or in limitations.
No No No No change in basic principles of operation, or a simple mechanical change. For example, change from dual magneto to two single magnetos on a model.
No No No Subsystem change produces no changes in base engine input parameters, and previous analysis can be reliably extended.
For example, a change in turbocharger where induction system inlet conditions remain unchanged, or if changed, the effects can be reliably extrapolated.
No No No
Appendix A A-53 The following are examples of NOT SIGNIFICANT changes for Engines (Parts 33 ):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Change in material of secondary structure or not highly loaded component. For example, a change from metal to composite material in a non-highly loaded component, such as an oil pan that is not used as a mount pad.
No No No Change in material that retains the physical properties and mechanics of load transfer. For example, a change in trace elements in a metal casting for ease of pouring or to update to a newer or more readily available alloy with similar mechanical properties.
No No No
Appendix A A-54
Table 4. Examples of Changes for Propellers (Parts 35)
The following are examples of SUBSTANTIAL changes for Propellers (Parts 35):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Change in the number of blades NA NA NA Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Appendix A A-55
The following are examples of SIGNIFICANT changes for Propellers (Part 35):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Principle of pitch change such as a change from single acting to dual acting Yes Yes Yes Requires extensive modification of the pitch change system with the introduction of back-up systems.
The inherent control system requires re-evaluation.
Introduction of a different principle of blade retention such as a single row to a dual row bearing
Yes Yes No Requires extensive modification of the propeller hub and blade structure.
The inherent strength requires re-evaluation.
A hub configuration change such as a split hub to a one piece hub Yes Yes No Requires extensive modification of the propeller hub structure.
The inherent strength requires re-evaluation.
Changing the method of mounting the propeller to the engine such as a spline to a flange mount Yes Yes No Requires extensive modification of the propeller hub structure.
Note: Such a change could be considered notsignificant if implemented without a change in general configuration or principals of construction.
Appendix A A-56 The following are examples of SIGNIFICANT changes for Propellers (Part 35):
Description of change Is there a change to the general configuration?
14 CFR §
21.101(b)(1)(i) Is there a change to the principles of construction?
14 CFR §
21.101(b)(1)(i) Have the assumptions used for certification been invalidated?
14 CFR §
21.101(b)(1)(ii) Notes Change in hub material from steel to aluminum Yes Yes No Requires extensive modification of the propeller hub structure and change to method of blade retention.
The inherent strength requires re-evaluation.
Change in blade material from metal to composite Yes Yes Yes Requires extensive modification of the propeller blade structure and change to method of blade retention. Composite construction methods required.
The inherent strength requires re-evaluation.
Change from hydromechanical to electronic control Yes Yes Yes Electronic manufacturing and design methods required.
Assumptions used for certification are no longer valid or were not addressed in the original certification,
i.e., high intensity radio frequency (HIRF) and lightning protection, fault tolerance, software certification and other aspects.
The propeller will require special conditions under 14 CFR § 21.16.