Fejin Emergency Equipment Section 4. Inspection of Propellers Section 6. Corrosion Preventative Maintenance Section 5. Using the table of contents below, click on a link to review the appropriate section: Corrosion Removal Procedures Section 7.
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Technical data 2. Introduction Anyone who intends to modify or change an aircraft, or any type certificated product, is confronted with rules, procedures, and terminology that may be confusing. Questions are raised such as follows. The design change process requires judgement and a good understanding of the applicable Civil Aviation Rules.
The licensed aircraft maintenance engineer is required to use experience, training, and familiarity with the rules to complete the various activities involved. The CAA, holders of inspection authorisations and certificated Part Design Organisations are others who may play a part in the process and be called upon for assistance. This advisory circular provides guidance on— a the technical data to use to embody a design change, in section 4 of this advisory circular b the process of applying for approval of a design change by the approval of the associated technical data, in section 4 of this advisory circular c determining if a modification is major or not, in section 5 of this advisory circular d completing the form CAA in section 6 of this advisory circular 3.
Design Changes: Modifications and Repairs 3. However, it is important to differentiate between a design change to an aircraft and maintenance which ensures the continued airworthiness of an aircraft.
Part 1 defines a design change as a change to the type design. In other words, has the aircraft or component changed from how it left the factory or from how the original manufacturer designed it? For example, the addition of a skin doubler repair patch or the replacement of a GPS unit with a newer model are design changes.
Maintenance is ensuring the aircraft or component stays airworthy as designed. For example, replacing a faulty piece of equipment with an identical, airworthy component or carrying out routine inspections, are maintenance activities. The first question to ask is whether or not the work being performed is a design change or simply maintenance?
Figure 1: Initial decision process for a design change As mentioned above, Part 43 provides for the practical application of design changes in the aircraft maintenance environment.
It is Part 21 Certification of Products and Parts that provides the certification basis and the procedures that enable design changes to be approved. Aircraft and other type certificated products can be changed in a number of ways.
These are design changes that are proposed by the type certificate holder. Part 21 Subpart D provides the process and criteria for changes to a type certificate.
This type of design change is typically issued as a service bulletin. These are design changes that are usually but not always developed by some-one other than the type certificate holder. Supplemental type certificates can be proposed by anyone and would typically include those proposals that form a kit to be sold for incorporation by third parties into a type certificated product. These are a design change required to rectify a discrepancy, usually on an individual aircraft, and often structural.
A repair, while resulting in a change to the type design, is intended to restore the product to the same operational capability as before. For example by the addition of a skin doubler and fasteners to restore strength to a cracked panel, or by a bush in a worn bearing component. These are design changes that are not changes to type certificates nor supplemental type certificates. Although the term modification is often used generally by industry to describe any design change.
Like repairs, modifications are normally individual changes, although under specific conditions modifications can be duplicated on aircraft of identical make, model and modified configuration. Modifications are approved by approving the technical data in accordance with Part 21 Subpart N. This advisory circular covers the approval process for modifications and repairs only. Firstly the technical data used to manufacture and install the change must be acceptable and secondly, the effect of the modification must be classified that is major or not.
The simplified process is shown in Figure 2. Figure 2. Simplified Modification or Repair Process Acceptable technical data? Rule If the modification or repair is not defined by approved or acceptable technical data then, referring to Figure 2, to proceed with the embodiment of the modification, approval of the data is first required.
The approval of technical data in accordance with Part 21 Subpart N may be done by the Director or a certificated Part Design Organisation who employs a senior person holding a delegation from the Director to approve modifications and repairs. Acceptable technical data and the technical data approval process are discussed further in section 4 of this advisory circular.
Is the modification or repair major? The embodiment of the design change must then be assessed for the possible effect of a failure. This is done using the criteria given in the definition of a major modification or repair. The assessment is made using the experience and judgement of the licensed aircraft maintenance engineer involved. Consideration should be given to the type of modification, the difficulty of application, the likelihood of an error being introduced, and other safety implications.
Referring to Figure 2, when the modification is determined to be major, an IA or a person authorised by a certificated Part Maintenance Organisation, will have to be consulted and used to certify conformity of the major modification to the acceptable technical data. Section 5 of this advisory circular provides further guidance on the definition of a major modification or repair. Firstly, Part 21 specifies the use of the form CAA for the approval of technical data.
Secondly, Part 43 Subpart E specifies the use of the form CAA to record the check of a major modification for conformity with the acceptable technical data.
Once the conformity inspection and the form CAA have been completed, the CAA form must be included in the aircraft maintenance records required by rule The form CAA provides sufficient detail to maintenance persons and the IA when assessing the continuing airworthiness of the airframe, engines, propellers, rotors, and other equipment.
This advisory circular examines the form CAA in particular but the requirements should be read across to those certificated Part Maintenance Organisation or certificated Part Design Organisations using other forms, for conformity or approval respectively.
Section 6 of this advisory circular provides detailed instructions for filling out the form CAA Technical Data 4. This enables it to be manufactured and installed on an aircraft, and to be used for conformity for any design change classified as a major modification or major repair. This list basically includes: a technical data that has been approved by the Director b technical data that other people have approved and that the Director has found acceptable to use c technical data that the Director has reviewed and found acceptable to use To have something approved and to have something accepted both require the presentation of that data to the Director.
The obvious difference is that the Civil Aviation Rules has defined approved to mean approved in writing by the Director unless used with reference to another person. Part 21 Appendix D places conditions on the use of acceptable data that include: a the data must be appropriate to the product, component, or appliance, and directly applicable to the work being carried out b for a foreign supplemental type certificate or supplemental type approval the data must— 1 not introduce a complete new flight manual because the flight manual is referenced on the airworthiness certificate.
This is to ensure the same certification basis was used for approval of the STC. This also means having the same certification category. For example: an STC approved in the restricted category would not be acceptable technical data for an aircraft which had been type accepted in the standard category. NOTE: STCs which do not meet the above conditions, or which are from a country not listed in Appendix D, may still be eligible for acceptance under rule An application should be made to the Director for review and acceptance of the data.
So that the holder can contact the installer on matters of continuing airworthiness. Acceptable technical data is not necessarily in a form that is able to be used immediately. For example, AC states that the use of non-aeronautical lead acid batteries is acceptable. This does not say that the installation of non-aeronautical lead acid batteries is approved in all aircraft. For the particular installation the technical data describing the actual installation would require approval as a design change.
Another example of inappropriate use of acceptable technical data is the installation of electrical equipment where that equipment has the possibility of overloading the aircraft electrical system. This is often forgotten but is just as important as checking for weight and balance effects.
In some cases, the acceptable technical data may not contain enough detailed information for the installation to proceed, for example, approved model list AML STCs are a class of STC issued by the FAA that approve a particular modification often across a large range of different makes and models of aircraft.
Since these STCs are based on the type design configuration, situations may arise where an aircraft configuration may have been altered in service by other modifications which may mean that the STC is not compatible with the current aircraft configuration.
In these situations, the installation instructions may not provide sufficient detail for the work to proceed, or it may not be possible to fully embody all aspects of the STC.
In these cases, the installation must not proceed until the STC has been revised or technical data for the differences has been approved. Subject to the conditions on the use of technical data, the following are acceptable technical data: a Type certificate data sheets. For example: approved drawings issued by the type certificate holder. Note: This includes data provided by the manufacturer of a component of a product where that component is a part of the approved type design of the product.
A similar notice is listed in the AS type acceptance report. Note: The list above contains data additional to that included in Part 21 Appendix D, plus some further explanatory material and examples. As a general rule, the test as to whether any technical data issued by a manufacturer is covered by this list is whether it has been approved.
For example a signed and approved drawing would be considered part of the approved type design, as would a formal modification bulletin. However a letter from their sales support department saying it is a good idea, would not. Neither would a letter from their design office stating that the office had no objection to the technical change.
However, as the data must still be reviewed and approved by either the Director or a certificated Part Design Organisation, the developer should consult with the approving organisation at an early stage to ensure the data will be suitable for approval and use. Note: The Director will only accept applications to approve technical data for minor modifications or repairs which do not require any flight testing or compliance inspections, and for which the documentation is complete.
For all applications, a minimum application period of 60 days will apply prior to the CAA reviewing the application. Alternatively, the applicant can seek a certificated Part Design Organisation for the review and approval of the technical data. Development of data As the modification is developed the assembled technical data forms the modification or repair package.
This package includes descriptive data, compliance data, operating and maintenance data and any other data needed to support the embodiment of the modification.
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