CS 25.605 Fabrication methods

Examples of fabrication method processes that may require close control to consistently produce safe parts include the following: castings, composite resin transfer methods, bonding, welding, heat-treating, or additive manufacturing methods. Fabrication method process specifications should include all critical inspection steps and/or process controlled steps, and should be substantiated (they may require re-evaluation and new substantiation, if modified later). All the inherent part characteristics that result from the fabrication method and affect the material strength and other properties should be closely correlated with non-destructive inspection (NDI) and/or process control variables. Furthermore, the applicant should show that the equipment used to support the process-critical manufacturing steps (particularly those steps that are not directly supported and controlled through inspection) is under appropriate process control, to ensure the consistent production of safe parts. Note 1: ‘safe parts’ must comply with CS 25.603 and CS 25.605 to ensure safety by maintaining the appropriate ‘material strength and other properties’ that are assumed in the design data. Therefore, applicants are reminded that, beyond the consideration of airframe strength, these CSs are also applicable to other applications for which safety relies on strength or stiffness, e.g. system structures. Furthermore, the reference to ‘other properties’ is intended to ensure that safety is also maintained for applications for which safety relies on ‘other properties’ (for example, safe interior cabin parts that rely upon suitable flammability properties). Note 2: approved fabrication process specifications and approved material specifications can be, for example, industry or military specifications, or European Technical Standard Orders (ETSOs).

[Amdt No: 25/27]

The test programme should initially consider the material strength and other properties resulting from each new fabrication method (‘new’ means new to the industry, an applicant, or an application configuration). The scope of the test programme should include considering the potential for anisotropic properties unless the applicant has already established an understanding of these properties. The test programme that is required for the certification of new fabrication methods should be used to evaluate the critical process variables. Based on that evaluation, the applicant should establish in the fabrication specifications the relevant parameters that govern the final material strength and other properties of the part at the time of its production and throughout its operational life. Furthermore, the applicant should evaluate the sensitivity of the material strength and other properties to the critical process variables to ensure that the established parameters are both robust and practical. Note: the test programme may also be used to help applicants understand the defect types and damage modes to be considered when showing compliance with other specifications, e.g. CS 25.571. Understanding the potential defects and damage modes is particularly important for sensitive fabrication processes, e.g. those used for structural bonding.

[Amdt No: 25/27]