Appendix A A-21
Table 2. Examples of Changes for Transport Airplanes (Part 25)
The following examples are for SUBSTANTIAL changes for Transport Airplanes (Part 25):
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 or location of engines, e.g., four to two wing-mounted engines or two wingmounted to two body-mounted engines
NA NA NA Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Change from a highwing to low-wing configuration NA NA NA Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Change from an all metal airplane to all composite primary structure (fuselage, wing, empennage) NA NA NA Proposed change in design is so extensive that a substantially complete investigation of compliance with the applicable regulations is required.
Change of empennage configuration for larger airplanes (cruciform vs. ‘T’ or ‘V’ tail) 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-22 The following examples are for SUBSTANTIAL changes for Transport Airplanes (Part 25):
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 from subsonic to supersonic flight regime 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-23
The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Reduction in the number of flight crew (In conjunction with flight deck update) No No Yes Extensive changes to avionics and aircraft systems. Impact to crew workload and human factors, pilot type rating.
Modify an airplane for flight in known icing conditions by adding systems for ice detection and elimination Yes No Yes New aircraft operating envelope. Requires major new systems installation and aircraft evaluation. Operating envelope changed.
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.
Increase in cabin pressurization No No Yes Typically, a change greater than 10% in operational cabin pressure differential.
May require extensive airframe changes affecting load paths, fatigue evaluation, aeroelastic characteristics, etc. Invalidates design assumptions.
Appendix A A-24 The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Addition of leading edge slats Yes No No Requires extensive changes to wing structure, adds aircraft systems, and requires a new airplane flight manual to address performance and flight characteristics.
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.
Appendix A A-25 The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Extensive structural airframe modification, such as installation of a large telescope with large opening in fuselage Yes No No Requires extensive changes to fuselage structure, affects aircraft systems, and requires a new airplane flight manual to address performance and flight characteristics.
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 Requires extensive changes to aircraft structure, affects aircraft systems, and requires new aircraft flight manual changes.
Primary structure changes from metallic material to composite material No Yes No Change in principles of construction and design from conventional practices.
Airframe life extension No No Yes This modification pertains to fuselage and/or wing limits, and aging airplane concerns.
It results in an increase from the original life limit which constitutes a reevaluation of certification design assumptions.
Appendix A A-26 The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Typically, an increase in design weight of more than 10 percent No No Yes Requires extensive resubstantiation of aircraft structure, aircraft performance and flying qualities and associated systems.
Installation of winglets
Yes No Yes Wing changes in span, sweep, tip designs or wing chord
Yes No Yes When it requires extensive changes to wing structure, adds aircraft systems, and requires a new airplane flight manual to address performance and flight characteristics.
(Note: Potentially substantial if it is a change from a high wing to a low wing, or a new wing.)
Change in type or number of emergency exits or an increase in the maximum certificated number of passengers
Yes No Yes The new emergency egress requirements exceed those previously substantiated.
Appendix A A-27 The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Comprehensive flight deck upgrade, such as conversion from entirely federated, independent electromechanical 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.
Change in primary flight controls to fly by wire (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 flight crew workload, handling qualities, and performance evaluation, which are different from the original design assumptions.
Appendix A A-28 The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Replace reciprocating with turbo-propeller engines Yes No No Requires extensive changes to airframe structure, addition of aircraft systems, and new airplane flight manual to address performance and flight characteristics.
Typically a thrust increase of more than 10 percent
No No Yes Requires resubstantiation of powerplant installation, and has a marked affect on aircraft performance and flying qualities.
Initial installation of an autoland system No No Yes Baseline airplane not designed for autoland operation, potential crew workload and systems compatibility issues.
Installation of a new fuel tank, (horizontal stabilizer tank or auxiliary fuel tank in the fuselage outside the wing in conjunction with increased maximum takeoff weight and takeoff thrust) No No Yes Requires changes to airframe, systems and Requires a new aircraft flight manual (AFM).
Results in performance changes.
Appendix A A-29 The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Main deck cargo door installation Yes No No Redistribution of internal loads, change in aeroelastic characteristics, system changes.
Expansion of an aircraft’s operating envelope
No No Yes An appreciable expansion of operating capability would normally be a significant change (e.g., an increase in maximum altitude limitation, approval for flight in known icing conditions, or an increase in airspeed limitations). Merely operating a product to an expanded envelope 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.
Appendix A A-30 The following examples are for SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Conversion from a passenger floor to a cargo floor and installation of a cargo handling system No No Yes Completely new floor loading and design.
Redistribution of internal loads, change in cabin safety requirements, system changes.
Initial installation of an auxiliary power unit (APU) essential for aircraft flight operation No No Yes Changes emergency electrical power requirements, change in flight manual and operating characteristics.
Conversion from hydraulically actuated brakes to electrically actuated brakes No No Yes Assumptions of certification for airplane performance are changed.
Change to airplane’s cabin operating altitude, or operating pressure
No
No Yes An increase greater than 10% in maximum cabin pressure differential invalidates certification assumptions and the fundamental approach used in decompression, structural strength, and fatigue.
Installation of engine thrust reversers Yes No Yes
Appendix A A-31
The following examples are for NOT SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Alternate engine installation or hush kit at same position No No No Typically it is not significant so long as there is not more than a 10 percent increase in thrust or a change in the principles of propulsion.
A small change in fuselage length due to refairing the aft body or radome No No No For cruise performance reasons, where such changes do not require extensive structural, systems, aerodynamic, or aircraft flight manual (AFM) changes.
Refairing of wing tip caps (for lights, fuel dump pipes) and addition of splitter plates to the trailing edge thickness of the cruise airfoil No No No Does not require extensive structural, AFM, or systems changes.
Additional power used to enhance high altitude or hot day performance No No No Usually no change in basic operating envelope.
Existing certification data can be extrapolated. Could be significant product change if the additional power is provided by installation of a rocket motor or additional, on demand engine due to changes in certification assumptions.
Appendix A A-32 The following examples are for NOT SIGNIFICANT changes for Transport Airplanes (Part 25):
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 Installation of an autopilot system No No See note It may be possible that the modification is adaptive in nature, with no change to original certification assumptions. However, in certain cases the installation of an autopilot may include extensive changes and design features which change both the general configuration and the assumptions for certification
(i.e., installation of the autopilot may introduce a number of additional mechanical and electronic failure modes and change the hazard classification of given aircraft level failures).
Change from assembled primary structure to monolithic or integrally machined structure No No No Method of construction must be well understood.
Modification to ice protection systems No No No Recertification required, but certification basis is adequate.
Brakes: design or material change, e.g., steel to carbon No No No Recertification required, but certification basis is adequate.