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5.4 Predecessor Regulations.
The airworthiness requirements in effect on the date of application are in parts 21, 23, 25, 27, 29, 31, 33, and 35. Consequently, when electing to comply with later requirements, the predecessor regulations (i.e., Civil Air Regulations (CARs)) are not considered in effect on the date of application. Predecessor regulations are not recognized under § 21.101(a), but may be allowed under § 21.101(b), (c), and (f).When choosing the amendment level of a regulation, all related regulations associated with that amendment level would have to be included.
5.5 Special Conditions, § 21.101(d).
Section 21.101(d) allows for the application of special conditions, or for changes to existing special conditions, to address the changed designs where the proposed certification basis does not provide adequate standards for an area, system, component, equipment, or appliance related to the change. The objective is to achieve a level of safety consistent with that provided for other areas, systems, components, equipment, or appliances affected by the change by the other requirements of the proposed certification basis. The application of special conditions to a design change is not, in itself, a reason to classify it as either a substantial change or a significant change. When the change is significant with earlier requirements allowed through exceptions, or not significant, the level of safety intended by the special conditions must be consistent with the agreed certification basis.
5.6 Effective Period for an Application to Change a Type Certificate, § 21.101(e).
According to § 21.101(e), an application for, or a change to, a TC for transport category aircraft is effective for five years from the date of application, and an application for a change to any other type certificate is effective for three years. The FAA intended this to ensure that the certification basis for the changed product is as current as practicable.
5.6.1 If the FAA has not approved a design change, or if it is clear that the FAA will not approve the change, within the time limit, the applicant may do either of the following:
(1) file for a new application, or (2) file for an extension to the original application.
5.6.2 When filing an extension, the applicant must choose a completion date, then apply the applicable effectivity from § 21.101(e) to determine an effective application date. The effective application date must not precede the original date of application for the proposed design change and must not be later than the filing date for an extension.
5.6.3 If you request an extension to the application date, and the product change is significant, a new certification basis is required. The new certification basis requires the additional latest regulations effective through the new application extension date. However, the applicant may use earlier regulations by documenting justification that the latest regulations for the change would not contribute materially to the level of safety or would be impractical.
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5.6.4 If the product change is not significant, you may continue to use the existing certification basis for product certification. However, if you make additional design changes to the product, and the FAA finds the existing certification basis for the change inadequate, the new certification basis will require later appropriate standards.
5.7 Other Category Aircraft, § 21.101(f).
For aircraft type certificated under §§ 21.17(b), 21.24, 21.25, and 21.27, the certification basis for the changed product consists of the amendment levels of the applicable regulations that the FAA finds appropriate for the change in effect on the date of application for the change. When selecting a certification basis for a change, you can propose compliance to an earlier amendment using the provisions of § 21.101(b).
The exceptions in § 21.101(c) do not apply to categories of products defined in § 21.101(f).
5.7.1 Special Classes Aircraft.
For special classes of aircraft (e.g., gliders, airships, etc.) including any installed engines and propellers certificated pursuant to § 21.17(b), the applicable requirements are portions of those other airworthiness requirements in parts 23, 25, 27, 29, 31, 33, and 35 that the FAA finds appropriate for the aircraft and applicable to the specific type design, or such airworthiness criteria that the FAA finds an equivalent level of safety to those parts.
5.7.2 Primary Category Aircraft.
For primary category aircraft certificated under § 21.24, the applicable airworthiness requirements are in parts 23, 27, 31, 33, and 35, or such other requirements the FAA finds appropriate. These requirements must be applicable to the specific design and intended use of the aircraft and provide a level of safety acceptable to the FAA.
5.7.3 Restricted Category Aircraft.
For aircraft certificated in the restricted category under § 21.25(a)(1), the application of the latest regulations typically would be considered not to contribute materially to the level of safety or be practical for its intended use. However, if the airworthiness regulations applicable to the aircraft at the time the TC was issued do not provide an adequate level of safety for the design change, the application of later regulations will be required.
5.7.3.1 Features of the changed product that are “novel” or “unusual” to the original certificated restricted category product may be assessed against a later requirement that addresses the feature. In this case, the applicable airworthiness requirements in effect at the time of the existing restricted category TC may be viewed as a starting point, with subsequent amendments being examined, if necessary, to arrive at a requirement that provides an appropriate level of safety.
5.7.3.2 For the installation of turbo-propeller engines instead of reciprocating engines (either in a restricted category aircraft that was originally
5-4 certificated based on satisfactory military service experience or in a restricted category aircraft for which the original certification basis did not contain regulations for turbine engine installations), later amendments will be used to provide an appropriate level of safety for its intended operation.
In addition, any change to the aircraft must be shown to be “safe for its intended use” as required by § 21.25. See Order 8110.56A, Restricted Category Type Certification, for additional details.
5.7.3.3 If the design change includes a new special purpose, it may require a re-evaluation of the regulations for certification. See Order 8110.56A, Chapter 3.
5.7.4 Military Aircraft Designs.
Aircraft type certificated in the restricted category under § 21.25(a)(2) are accepted on the basis of the U.S. military use and other eligibility factors, instead of showing compliance with airworthiness standards in 14 CFR Chapter 1. (See Order 8110.56, Chapter 4, for additional details.) Many of these aircraft were not certificated to airworthiness standards; therefore, any modifications made to the military configuration must meet an equivalent civil certification basis derived from the airworthiness regulations contained in 14 CFR. This baseline certification basis is the airworthiness regulations (i.e., parts 23, 25, 27, 29, 33, or 35, or CARs, as appropriate) that were in effect on the date that the first military model was accepted for operational use by the U.S. Armed Forces. Section 21.101(f) requires the application of the latest amendments to significant changes to these products. However, since the latest amendments may not be appropriate for the aircraft’s intended use, earlier regulations are acceptable. They cannot predate the equivalent certification basis. If these regulations do not include airworthiness standards applicable to the change, later regulations appropriate to the product category will be applied. In addition, any design change to the aircraft must be shown to be “safe for its intended use” as required by § 21.25. See Order 8110.56A for additional details.
5.7.5 Surplus Military Aircraft.
Aircraft type certificated under § 21.27 are entitled to a TC in the normal, utility, acrobatic, commuter, or transport category. These aircraft were designed and constructed in the United States, accepted for operational use, and declared surplus by the U.S. Armed Forces. These aircraft may be counterparts, and are considered equivalent, to the previously civil certificated aircraft. Product changes or modifications to these aircraft are certificated in the same manner as their civil counterparts.
5.7.6 Limited Category Aircraft.
Limited category aircraft are surplus military aircraft, mostly from World War II, that were type certificated under CAR part 9 for use other than air transport. These aircraft are not permitted to carry persons or property for hire, and were accepted based on their previous military qualifications. A change to aircraft not supported by the military service history must comply with appropriate airworthiness standards. The level of safety associated with earlier standards may be acceptable for limited category aircraft.
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5.8 Clarification of § 21.101(g), Part 26 Requirements.
5.8.1 Part 26 establishes requirements for support of continued airworthiness of and safety for transport category airplanes. The applicant must show compliance with each applicable provision of part 26, unless the applicant has elected or was required to comply with a corresponding amendment to part 25 that was issued on or after the date of the applicable part 26 provision. Section 21.101(g) does not allow an applicant to use an exception under § 21.101(b) for relief from complying with the applicable provisions of part 26.
5.8.2 The language in § 21.101(g) also recognizes that future part 25 amendments will be issued after the requirements in part 26 are established. Consequently, an applicant may be required to comply with a later part 25 amendment. Section 21.101(g) does not contain exception provisions for reverting to earlier part 26 requirements. However, under § 21.101(b) instead of complying with a later part 25 requirement, an applicant may be allowed to comply with an earlier part 26 or earlier part 25 requirement if justification is provided.
5.9 Documentation.
5.9.1 Documenting the Proposal.
In order to efficiently determine and agree upon a certification basis with the FAA, the following information is useful to understand your position:
• The current certification basis of the product you are changing, including amendment level.
• The amendment level of all the applicable airworthiness requirements at the date of application.
• Your proposed certification basis, including amendment levels.
• Description of the affected area.
• If you propose a certification basis that includes amendment levels earlier than what was in effect at the date of application, include the exception as outlined in § 21.101(b) and your justification if needed.
Please see appendix H for examples of optional tools you can use to document your proposed certification basis.
5.9.2 Documenting the Significant/Not Significant Decision.
5.9.2.1 The FAA determines whether the design changes are significant or not significant, and this decision is documented on the Certification Project Notification according to FAA Order 8110.115, Certification Project Initiation and Certification Project Notification. However, the FAA provides an optional decision record for the applicant to make a predetermination to facilitate the FAA decision. This form is provided in
5-6 appendix G of this AC and follows the flowchart in figure 3-1 of this AC.
If used, you should submit it along with the certification plan.
5.9.2.2 Design changes that are determined to be significant changes under § 21.101, the exceptions, and agreement of affected and unaffected areas is typically documented through the G-1 issue paper process. An example tool is provided in appendix H of this AC.
5.9.3 Documenting the Certification Basis.
5.9.3.1 The FAA will amend the certification basis for all design changes that result in a revision to the product’s certification basis on the amended TCDS or STC. The FAA will document the resulting certification basis because it is part of the compliance record required by FAA Order 8110.4C. For further information on documenting the certification basis, see FAA Order 8110.48A.
5.9.3.2 The FAA will document the certification basis of each product model on all STCs, including Approved Model List STCs.
5.10 Incorporation of STCs into the Type Design.
The incorporation of STCs into the product type design may generate an additional major change when that change is needed to account for incompatibility between several STCs that were initially not intended to be applied concurrently.
5.10.1 If the incorporation of the STC(s) does not generate an additional major change, the incorporation is not evaluated pursuant to § 21.101. The existing certification basis should be updated to include the later amendments of the STC(s) being incorporated.
5.10.2 If the incorporation of the STC(s) generates an additional major change, the change must be evaluated pursuant to § 21.101, and the existing certification basis should be updated to include the amendments resulting from the application of § 21.101.
5.11 Removing Design Changes.
Approved design changes may be removed after incorporation in an aeronautical product. These design changes will most commonly occur via an STC or service bulletin kit.
5.11.1 You should identify a product change that you intend at its inception to be removable as such, and you should develop instructions for its removal during the initial certification.
The FAA will document the certification basis for both the installed and removed configuration separately on the TCDS or STC.
5.11.2 If specific removal instructions and a certification basis corresponding to the removed condition are not established at the time of the initial product change certification, the removal of design changes or portions of those changes may constitute a significant
5-7 change to type design. A separate STC or amended TC may be required to remove modifications and the resulting certification basis established for the changed product.
5.12 The Certification Basis is Part of the Design Change.
A new design change may be installed in a product in production or via a service bulletin or STC. In terms of § 21.101, each of the approved design changes has its own basis of certification. If an applicant chooses to remove an approved installation
(e.g., interior installation, avionics equipment) and install a new installation, a new certification basis may be required for the new installation, depending on whether the change associated with the new installation is considered significant compared to the baseline configuration that the applicant chooses. If the new installation is a not significant change, the unmodified product’s certification basis may be used (not the previous installation certification basis), provided the certification basis is adequate. For example, a transport category airplane is certified as a “green” configuration. The airplane certification basis does not include § 25.562 if it was manufactured prior to October 28, 2009. An interior is installed under an STC, and the applicant elects to include § 25.562 (dynamic seats) in the certification basis to meet specific operational requirements. At a later date, the airplane is sold to a non-part 121 operator (i.e., does not have the same operating requirements). A new interior is installed; there will be no requirement for § 25.562 to be included in the new certification basis.
5.13 Sequential Design Changes—Cumulative Effects.
5.13.1 If you intend to accomplish a product change by incorporating several design changes in a sequential manner, you should identify to the FAA up front when the first application is made. In addition, the cumulative effects arising from the initial change, and from all of the follow-on changes should be included as part of the description of the change in the initial proposal. The classification of the intended product change will not be evaluated solely on the basis of the first application, but rather on the basis of all the required design changes needed to accomplish the intended product change. If the FAA determines that the current application is a part of a sequence of related changes, then the FAA will re-evaluate the determination of significance and the resulting certification basis as a group of related changes.
5.13.2 Example: Cumulative Effects—Advancing the Certification Basis.
The type certificate for airplane model X lists three models, namely X-300, X-200, and X-100. The X-300 is derived from the X-200, which is derived from the original X-100 model. An applicant proposes a design change to the X-300 airplane model. During the review of the X-300 certification basis and the regulations affected by the proposed change, it was identified that one regulation, § 25.571 (damage tolerance requirements), remained at the same amendment level as the X-100 original certification basis (exception granted on the X-200). Since the amendment level for this particular regulation was not changed for the two subsequent airplane models (X-200 and X-300), the applicant must now examine the cumulative effects of these two previous design
5-8 changes that are related to the proposed change and the damage tolerance requirements to determine whether the amendment level needs to advance.
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.