Appendix C C-2 C.2 Physical Changes.
C.2.1 Steps.
• Step 1. Make a list of the physical changes.
• Step 2. List the corresponding airworthiness requirements applicable to the physical changes.
• Step 3. List the amendment level recorded on the existing certification basis of the baseline product and the amendments on the date of application.
C.2.2 Example.
The change is adding a winglet to a fixed wing aircraft and a change to the leading edge slats for a performance increase. As part of the change, you modify an electrically driven slat actuator by changing the mounting structure of the actuator used to connect the actuator to the slat. The actuator structure is changed. The electrical system in the actuator is not affected. You would list airworthiness requirements applicable to the actuator. You would not list the airworthiness requirements applicable to the electrical system of the actuator. See table C-1 below for an example of how to chart a physical change and the associated airworthiness requirements.
Table C-1. Example of Associating a Physical Change with the Applicable Airworthiness Requirements Physical Change Applicable Regulations* Amendment of Existing Certification Basis Amendment on Application Date Structural change to slat actuator § 25.xxx 25-aaa 25-ddd § 25.yyy 25-bbb 25-eee § 25.zzz 25-ccc 25-fff * These would be airworthiness requirements related to structural aspects only.
C.3 Functional Changes.
C.3.1 Steps.
• Step 1. Describe each change.
• Step 2. Describe the effects of the change (e.g., structural, performance, electrical, etc.).
• Step 3. List the areas, system, component, and appliance that are affected by that effect.
Appendix C C-3
• Step 4. List the airworthiness requirements associated with the effect for each area, system, component, or appliance.
• Step 5. List the amendment level recorded on the existing certification basis of the baseline product and the amendments on the date of application.
C.3.2 Example.
The change is adding a winglet to a fixed wing aircraft and a change to the leading edge slats for a performance increase. The wing root bending moment has increased. The loads in the wing box are increased but the wing box has sufficient structural margins to carry the higher loads. Thus, the wing box is not physically changed but its function has changed because it carries greater loads. See table C-2 below for an example of how to chart a functional change, its effects, and the affected areas (steps 1 through 3 above).
See table C-3 below for an example of how to chart an area affected by a functional change and the associated airworthiness requirements (steps 4 and 5 above).
Table C-2. Example of a Functional Change, Affected Areas, and Associated Effects Description of Change Effects Affected Areas Installation of winglet Increased loads in wing structure Wing spars Wing skins Effect 2* Area 1 Area 2 Effect 3* Area 3 * There may be other effects as well.
Appendix C C-4 Table C-3. Example of Associating Affected Areas with the Applicable Airworthiness Requirements Impacted Area Applicable Regulations* Amendment of Existing Certification Basis Amendment on Application Date Wing spar § 25.xxx 25-aaa 25-ddd § 25.yyy 25-bbb 25-eee § 25.zzz 25-ccc 25-fff * These would be structural airworthiness requirements only. There could be other requirements applicable to the wing box. But since the effect is structural, then only the structural requirements are applicable.
C.4 Combine the Lists.
C.4.1 The FAA typically presents the certification basis for a product by regulation and not by area. The next step is to combine these two lists. However, since you are only changing a portion of the product, you will need to identify the changed and affected area of the new certification basis. The unchanged area is not required to comply with the airworthiness requirements in effect at the date of application. (See § 21.101(b)(2).)
C.4.2 When the change is quite extensive, you will save time by listing all the airworthiness requirements applicable to the category of product you are certifying. You can use table C-4 below in the next step where you will identify other exceptions you would like the FAA to consider.
C.4.3 Example.
If we use the examples above for the combined list for the actuator structural changes and the wing box functional change, then you would list the certification basis as shown in table C-4 below.
Appendix C C-5 Table C-4. Example of a Combined List of Physical and Functional Changes with Applicable Airworthiness Requirements Amendment Levels Amendment of Existing 14 CFR Certification Amendment on Section Basis Application Date Change and Affected Area § 25.xxx* 25-aaa 25-ddd • Wing spar § 25.yyy* 25-bbb 25-eee •
• Leading edge actuator Wing loads § 25.zzz* 25-ccc 25-fff * These represent structural requirements.
Appendix D D-1 APPENDIX D. OTHER GUIDANCE FOR AFFECTED AREAS D.1 Sample Questions in Determining Affected Areas.
Below are sample questions to assist in determining whether an area is affected by the change. If the answer to any of these questions is yes, then the area is considered affected.
1. Is the area changed from the identified baseline product?
2. Is the area impacted by a significant product level change?
3. Is there a functional effect on the unchanged area by a change to the system or system function that it is a part of?
4. Does the unchanged area need to comply with a system or product level requirement that is part of the change?
5. Are the product level characteristics affected by the change?
6. Is the existing compliance for the area invalidated?
D.2 Sub-Areas within an Affected Area.
Within areas affected by a change, there may be “sub-areas” of the area that are not affected. For those sub-areas, the amendment levels at the existing certification basis remain valid, along with the previous compliance findings. For example, if a passenger seat fitting is changed as part of a significant change, then the structure of the seat is affected. Thus, the amendment level for §§ 25.561 and 25.562, along with other applicable structural requirements, would be at the amendment level on the date of application (unless an exception is granted). However, the seat fabric is not affected, so the amendment level for § 25.853 (flammability) may remain at the existing certification basis, and a new compliance finding would not be required.
Appendix E E-1 APPENDIX E. PROCEDURE FOR EVALUATING MATERIAL CONTRIBUTION TO SAFETY
OR IMPRACTICALITY OF APPLYING LATEST REQUIREMENTS
TO A CHANGED PRODUCT E.1 Introduction.
E.1.1 The basic principle of enhancing the level of safety of changed aeronautical products is to apply the latest regulations for significant design changes to the greatest extent practical. In certain cases, the cost of complying fully with a later regulation may not be commensurate with the small safety benefit achieved. These factors form the basis where compliance with the latest standard may be considered impractical, thereby allowing compliance with an earlier regulation. This appendix gives one method of determining if compliance with a later regulation is impractical; however, it does not preclude the use of other methods for improving the safety of aeronautical products.
E.1.2 The FAA recognizes that other procedures can be used and have historically been accepted on a case-by-case basis. The acceptance of results through the use of these procedures may vary from State to State. Consequently, they may not be accepted through all bilateral certification processes. Regardless of which method is used, the process must show that a proposed certification basis is able to achieve a positive safety benefit for the overall product.
E.1.3 In regard to impractical, any method used must encourage incorporating safety enhancements that will have the most dramatic impact on the level of safety of the aircraft while considering effective use of resources. This important point is illustrated graphically in figure E-1 below. This figure notionally shows the interrelation between the total resources required for incorporating each potential safety enhancement with the corresponding net increase in safety benefit.
Appendix E E-2 Figure E-1. Safety Benefits versus Resources
E.1.4 Typically, you will find that, for impractical, there are proposals that can achieve a positive safety benefit that are resource effective. Conversely, there are proposals that may achieve a small safety benefit at the expense of a large amount of resources to implement. Clearly, there will be a point where a large percentage of the potential safety benefit can be achieved with a reasonable expenditure of resources. The focus of the methods used should be to determine the most appropriate regulatory standards relative to the respective incremental cost to reach this point.
E.1.5 This appendix provides procedural guidance for determining the material contribution to the level of safety, or the practicality of applying a requirement at a particular amendment level to a changed product. The procedure is generic in nature and describes the steps and necessary inputs that you can use on any project to develop a position.
E.1.6 The procedure is intended to be used, along with good engineering judgment, to evaluate the relative merits of a changed product complying with the latest regulations.
It provides a means, but not the only means, for you to present your position regarding an exception under § 21.101(b)(3).
E.1.7 The certification basis for a change to a product will not be at an amendment level earlier than the existing certification basis or any requirement found in §§ 23.2, 25.2,
27.2, and 29.2, or part 26, that is related to the change.
Appendix E E-3 E.2 Procedure for Evaluating Material Contribution or Impracticality of Applying Latest Requirements to a Changed Product.
The following are steps to determine the material contribution or impracticality of applying a requirement at a particular amendment level.
E.2.1 Step 1: Identify the Regulatory Change being Evaluated.
In this step, document— E.2.1.1 The specific requirement (e.g., § 25.365), E.2.1.2 The amendment level of the existing certification basis for the requirement, and E.2.1.3 The latest amendment level of the requirement.
E.2.2 Step 2: Identify the Specific Hazard that the Requirement Addresses.
E.2.2.1 Each requirement and subsequent amendments address a hazard or hazards. In this step, the specific hazard(s) is identified. This identification will allow for a comparison of the effectiveness of amendment levels of the regulation at addressing the hazard.
E.2.2.2 In many cases, the hazard and the cause of the hazard will be obvious.
When the hazard and its related cause are not immediately obvious, it may be necessary to review the preamble of the regulation. It may also be helpful to discuss the hazard with the responsible FAA office.
E.2.3 Step 3: Review the Consequences of the Hazard(s).
E.2.3.1 Once the hazard is identified, it is possible to identify the types of consequences that may occur due to the hazard. More than one consequence can be attributed for the same hazard. Typical examples of consequences would include, but are not limited to—
• Incidents where only injuries occurred,
• Accidents where a total hull loss occurred,
• Accidents where less than 10 percent of the passengers died,
• Accidents where 10 percent or more passengers died, and
• Engine- and propeller-specific hazards.
E.2.3.2 The preamble to the regulation may provide useful information regarding the consequences of the hazard that the requirement addresses.
Appendix E E-4 E.2.4 Step 4: Identify the Historical and Predicted Frequency of Each Consequence.
E.2.4.1 Another source for determining impracticality is the historical record of the consequences of the hazard that led to a requirement or an amendment to a requirement. From these data, a frequency of occurrence for the hazard can be determined. It is important to recognize that the frequency of occurrence may be higher or lower in the future. Therefore, it also is necessary to predict the frequency of future occurrences.
E.2.4.2 More than one consequence can be attributed for the same hazard.
Therefore, when applicable, the combination of consequences and frequencies of those consequences should be considered together.
E.2.4.3 The preamble of the regulation may provide useful information regarding the frequency of occurrence.
E.2.5 Step 5: Determine How Effective Full Compliance with the Latest Amendment of the Requirement would be at Addressing the Hazard.
E.2.5.1 When each amendment is issued, it is usually expected that compliance with the requirement would be completely effective at addressing the associated hazard for the designs and technology envisioned at the time. It is expected the hazard would be eliminated, avoided, or mitigated.
However, experience has shown that this may not always be the case. It is also possible that earlier amendment levels may have addressed the hazard but were not completely effective. A product may also contain a design feature(s) that provides a level of safety that approaches the latest regulations, yet is not fully compliant with the latest regulations.
Therefore, in comparing the benefits of compliance with the existing certification basis to the latest amendment level, it is useful to estimate the effectiveness of both amendment levels in dealing with the hazard.
E.2.5.2 It is recognized that the determination of levels of effectiveness is normally of a subjective nature. Therefore, prudence should be exercised when making these determinations. In all cases, it is necessary to document the assumptions and data that support the determination.
E.2.5.3 The following five levels of effectiveness are provided as a guideline:
1. Fully effective in all cases. Compliance with the requirement eliminates the hazard or provides a means to avoid the hazard completely.
2. Considerable potential for eliminating or avoiding the hazard.
Compliance with the requirement eliminates the hazard or provides a means to completely avoid the hazard for all probable or likely cases, but it does not cover all situations or scenarios.
Appendix E E-5
3. Adequately mitigates the hazard. Compliance with the requirement eliminates the hazard or provides a means to avoid the hazard completely in many cases. However, the hazard is not eliminated or avoided in all probable or likely cases. Usually this action only addresses a significant part of a larger or broader hazard.
4. Hazard only partly addressed. In some cases, compliance with the requirement partly eliminates the hazard or does not completely avoid the hazard. The hazard is not eliminated or avoided in all probable or likely cases. Usually this action only addresses part of a hazard.
5. Hazard only partly addressed but action has negative side effect.
Compliance with the requirement does not eliminate or avoid the hazard or may have negative safety side effects. The action is of questionable benefit.
E.2.5.4 If it is determined that compliance with the latest regulations does not contribute materially to the product’s level of safety, skip Step 6 of this appendix and go directly to Step 7 to document the conclusion. If it is determined that complying with the latest amendment of the regulation contributes materially to the product’s level of safety, continue to Step 6 of this appendix.
E.2.6 Step 6: Determine the Incremental Resource Costs and Cost Avoidance.
E.2.6.1 There is always cost associated with complying with a requirement. This cost may range from minimal administrative efforts to the resource expenditures that support full-scale testing or the redesign of a large portion of an aircraft. However, there are also potential cost savings from compliance with a requirement. For example, compliance with a requirement may avoid aircraft damage or accidents and the associated costs to the manufacturer for investigating accidents. Compliance with the latest amendment of a requirement may also help a foreign authority certificate a product.
E.2.6.2 When determining the impracticality of applying a requirement at the latest amendment level, only the incremental costs and safety benefits from complying with the existing certification basis should be considered.
E.2.6.3 When evaluating the incremental cost, it may be beneficial for you to compare the increase in cost of complying with the latest requirements to the cost of incorporating the same design feature in a new airplane. In many cases, an estimate for the cost of incorporation in a new airplane is provided in the regulatory evaluation by the FAA, which was presented when the corresponding regulation was first issued. Incremental costs of retrofit/incorporation on existing designs may be higher than that for production. Examples of costs may include, but are not limited to, the following:
Appendix E E-6 Costs The accuracies of fleet size projections, utilization, etc., may be different than that experienced for derived product designs and must be validated.
• Labor: Work carried out in the design, fabrication, inspection, operation, or maintenance of a product for the purpose of incorporating or demonstrating compliance with a proposed action.
Non-recurring labor requirements, including training, for the applicant supporting development and production of the product, should be considered.
• Capital: Construction of new, modified, or temporary facilities for design, production, tooling, training, or maintenance.
• Material: Cost associated with product materials, product components, inventory, kits, and spares.
• Operating Costs: Costs associated with fuel, oil, fees, training, and expendables.
• Revenue/Utility Loss: Costs resulting from earning/usage capability reductions from departure delays, product downtime, and performance loss due to seats, cargo, range, or airport restrictions.
• The cost of changing compliance documentation and/or drawings in itself is not an acceptable reason for an exception.
Cost Avoidance.
• Avoiding cost of accidents, including investigation of accidents, lawsuits, public relations activities, insurance, and lost revenue.
• Foreign Certification: Conducting a single effort that would demonstrate compliance to the requirements of most certifying Authorities, thus minimizing certification costs.
E.2.7 Step 7: Document the Conclusion.
With the information from previous steps documented and reviewed, the applicant’s position and rationale regarding whether complying with the latest regulations contributes materially to the product’s level of safety or its practicality can be documented. The FAA records the determination of whether the conditions for the proposed exception were met. That determination is based on the information and analysis provided by the applicant in the preceding steps. If the determination to grant the exception is based on the product’s design features, those features are documented at a high level in the TCDS. Documentation in the TCDS is required so that the features are maintained during subsequent changes to the product, therefore, maintaining the product’s agreed level of safety. If the results of this analysis are inconclusive, then further discussions with the FAA are warranted.
Appendix E E-7 E.3 Examples of How to Certify Changed Aircraft.
The following examples illustrate the typical process an applicant follows. The process will be the same for all product types.
E.3.1 Example 1: § 25.963, Fuel Tank Access Covers.
This example is part of a significant change to a transport airplane that increases passenger payload and gross weight by extending the fuselage 20 feet. To accommodate the higher design weights and increased braking requirements and to reduce runway loading, the applicant will change the landing gear from a two-wheel to four-wheel configuration; this changes the debris scatter on the wing from the landing gear. The FAA will require that the new model airplane comply with the latest applicable regulations based on the date of application.
The wing will be strengthened locally at the side of the body and at the attachment of engines and landing gear, but the applicant would not like to alter wing access panels and the fuel tank access covers. Although the applicant recognizes that the scatter pattern and impact loading on the wing from debris thrown from the landing gear will change, the applicant proposes that it would be impractical to redesign the fuel tank access covers.
Note: Sections 121.316 and 21.21(b)(2) may be additional reasons the FAA would require compliance with § 25.963(e), regardless of the significant determination.
E.3.1.1 Step 1: Identify the Regulatory Change being Evaluated.
The existing certification basis of the airplane that is being changed is part 25 prior to Amendment 25-69. Amendment 25-69 added the requirement that fuel tank access covers on transport category airplanes be designed to minimize penetration by likely foreign objects, and that they be fire resistant.
E.3.1.2 Step 2: Identify the Specific Hazard that the Regulation Addresses.
Fuel tank access covers have failed in service due to impact with high-energy objects such as failed tire tread material and engine debris following engine failures. In one accident, debris from the runway impacted a fuel tank access cover, causing its failure and subsequent fire, which resulted in fatalities and loss of the airplane. Amendment 25-69 will ensure that all access covers on all fuel tanks are designed or located to minimize penetration by likely foreign objects, and that they are fire resistant.
E.3.1.3 Step 3: Review the History of the Consequences of the Hazard(s).
There have been occurrences with injuries and with more than 10 percent deaths.