(3) Uncured Prepreg Requirements.
(a) The material specification includes requirements for uncured prepreg physical and chemical properties. A summary of the uncured prepreg property data, which can help establish requirements to control the processes, is given in a table in the DOT/FAA/AR-02/109.
Testing should be conducted on prepreg made to the upper and lower limits of the resin mixing, filming, and prepreg processes to help define the requirements. Testing to establish requirements also considers variability for samples taken from different locations within a spool of material.
(b) The material specification includes limitations and correction procedures for visual defects in the prepreg. Criteria for continuous defects that occur during prepreg production (e.g., gaps and fiber alignment) must be established and documented. Criteria for discontinuous defects (e.g., fuzz balls, splices, and foreign material) should also be defined. All procedures for defect removal or identification should be documented. The procedures for continuous inspection of the prepreg should be defined. When the user detects defects after removing the release paper when a part is being laid up, the same criteria for allowable defect limits and correction are followed.
(c) The material specification includes definitions and limitations for storage life, handling life, and out life. These requirements are based on either test data or experience, or both, with materials having similar chemical makeup. The supplier documents the storage/out life of a material from the date of manufacture until it arrives at the purchaser. This tracking includes resin intermediates, mixed resin, and film before prepreg process steps.
(d) Width and length tolerances for spools of prepreg material need to be defined.
The roll size, weight, width, and core type should be specified in either a purchasing document or the material specification. The specification has a procedure to identify, mark, and document all prepreg defects that are outside the allowable limits. Similarly, splices to remove defects are identified, marked, and documented for the user. The out time, time accumulated to disposition and remove defects, is recorded and used to adjust the remaining out life.
(4) Cured Prepreg Property Requirements.
(a) The material specification includes requirements for the cured prepreg in a laminate form. These requirements are based on specific data obtained for the material during qualification. The associated laminate process steps and a baseline cure cycle are defined for this purpose and documented in a corresponding process specification or other instructions. The cure process should consistently produce cured laminates of high quality. This cure cycle is used for all qualification and batch acceptance testing.
(b) The material specification includes requirements for cured laminate physical and mechanical properties. These requirements are based on qualification testing to characterize the material in a cured state. The goal is to provide a representative database, which is the basis for criteria applied in material acceptance and equivalency sampling. The limits and test methods for each property are documented in the specification. Perform some subset of the qualification 11
tests for each batch as a part of the continuous quality control process. Batch sampling should be able to identify possible variations in properties as a function of location in prepreg rolls.
(c) Discussions and tables in the DOT/FAA/AR-02/109 recommend a minimum set of cured laminate physical and mechanical property tests to establish the material specification.
This test matrix is similar to the AGATE test matrix in DOT/FAA/AR-00/47 and DOT/FAA/AR-03/19. (The primary difference relates to a recommended change in laminate lay-up in DOT/FAA/AR-02/109, which allows a less operator sensitive test for determining consistent longitudinal tension and compression strength data.)
(d) The physical properties include fundamental material characteristics such as cured ply thickness, laminate density, and constituent volume fractions, which are controlled to ensure a repeatable product. The void content and glass transition temperature tests provide additional confidence that the prepreg material is under control. Mechanical tests are able to detect changes in the fiber, resin, fiber/resin interface, and the response of the prepreg to the baseline cure process. They include base material moduli and strength tests for fiber and matrixdominated properties. A combination of tension, compression, and shear tests for a range of environmental conditions provide a minimum set for qualification purposes.
(e) Discussions and tables in the DOT/FAA/AR-02/109 recommend additional tests be run at some frequency to keep the test methodology current and to further populate the database. Some of these tests are used periodically to update the material acceptance and equivalency requirements in the specification to better represent the population. Others are used to expand the utility of the database for multiple applications. For example, additional laminate test data is recommended for layups and details (e.g., open hole, filled hole, and pin bearing), which are characteristic of design. Other test recommendations help characterize solvent sensitivity, laminate sandwich panels, interlaminar fracture toughness, laminate fatigue, postimpact residual strength, flammability, moisture diffusion, and thermal cycling. These additional tests are optional for inclusion in the material specification, but they may be required for the design and certification of an end-user's product. As a result, there is a potential for cost savings if the additional tests are shared among several end users.
c. Material Characterization.
(1) The material specification includes qualification procedures and methods to initially characterize the material. Tests must be conducted to create an initial database. A material supplier, an end user, or an industry consortium (a supplier and multiple users, e.g., AGATE) can perform the testing. The results from the testing are used to establish the initial material specification requirements and batch acceptance limits. The decision on whether the specification becomes an industry standard or an end-user proprietary specification is for the developers of the database to determine.
(2) The FAA reviews a request for the initial qualification. The organization that will conduct the tests submits a test plan, a material specification, and a process specification before the actual qualification. The material specification submitted for initial review will be without those final requirements, which depend on qualification test databases. Any parties interested in 12
FAA support must have clear evidence of potential applications that will request certification.
The initial request should be made to the geographically responsible Aircraft Certification Office (ACO). That office will then contact the Small Airplane Directorate to determine the most appropriate office to work on the qualification.
(3) The initial qualification database includes uncured prepreg and cured laminate properties that provide a baseline in key composite characteristics, which provide reliable measures that the material is under control. This includes a balanced combination of chemical, physical, and mechanical property tests that are sensitive to any significant changes in fiber, resin, fiber/resin interface and response of the prepreg to the baseline cure process. Minimum recommendations given in the DOT/FAA/AR-02/109 may be used as a guide.
(4) A minimum of three different material batches, consisting of a minimum of two different fiber batches and three different resin batches, is used for the initial database.
Laminates for mechanical property data for each batch are processed using a minimum of two independent cure cycles. Allowed limits in thermal history of prepreg material and accepted variations in the baseline cure cycle are considered in developing the qualification database. The data from each processing cycle can be considered a separate batch in following the statistical procedures given in DOT/FAA/AR-00/47, DOT/FAA/AR-03/19, and/or MIL-HDBK-17.
(5) The material property equivalency requirements and material batch acceptance limits may also use DOT/FAA/AR-00/47, DOT/FAA/AR-03/19, and/or MIL-HDBK-17. These documents recommend sample size and statistical parameters, which are discussed in the FAA material qualification and equivalency policy statement. Equivalency requirements for all tested properties, and acceptance limits for specified properties, are listed in the specification. In DOT/FAA/AR-02/109, the requirements and acceptance limits were recommended for the following:
• Maximum average, minimum average, and minimum individual values for all strength properties;
• Maximum and minimum average values for all stiffness properties;
• Maximum and minimum average values for cured laminate physical properties;
and
• Maximum average values for uncured prepreg properties.
(6) Although initial qualification tests can be completed with as few as three batches of prepreg, some additional testing to expand this database may help establish a more robust basis.
This is particularly important if the material is relatively new and the variation in initial qualification batches is not fully representative of full-scale prepreg production. Without a mechanism in the specification to recalculate material equivalency and batch acceptance limits based on more data, failures of material equivalency programs and batch rejections are possible.
If undesirable changes are occurring to the material and reducing key properties over time, periodic property testing will provide a safety benefit.
(7) DOT/FAA/AR-02/109 provides some recommendations for periodic property testing to expand the qualification basis. These procedures can be added to the material specification.
The material equivalency and batch acceptance limits may be recalculated to update the material specification periodically. For those properties tested for each batch of material, the data from all batches is included in the recalculation. The frequency of periodic property tests decreases over time as an accurate basis is achieved.
(8) In expanding a shared database from base material characterization to include additional data at material, laminate, and higher levels, some of the same engineering protocol remains valid. In particular, statistical parameters and acceptance criteria can be derived for each property or design value of interest. These engineering processes are then applied in equivalency sampling tests to demonstrate that new users can produce the material to that level of property or design value. If successful, the new user can share the expanded database. The keeper of a shared database has freedom to decide what properties should be added over time. In practice, additional laminates considered for an expanded database are characteristic of those typically used in product design.
d. Changes to Qualified Materials.
(1) Maintain consistent raw materials and processes to ensure repeatable aircraft product manufacturing. However, it is inevitable that some changes will occur throughout a production run due to economics or issues outside the control of suppliers and users. Since prepreg materials and processes will likely undergo continual evolution, establish procedures to evaluate the effects of changes.
(2) The material specification includes the procedures and associated requirements to deal with change, including the specific means to establish the equivalency of future material data to the baseline database. Material equivalency is the procedure of determining whether changes in the materials or processes yield enough similarity in the key characteristics and properties of a prepreg material that they can be used without distinction and without additional evaluation. Note that two materials that meet the same minimum requirements, but have statistically different mean properties, are not considered “equivalent.” MIL-HDBK-17, Volume 1, Section 8.4.1 (“Tests for Determining Equivalency Between an Existing Database and a New Dataset for the Same Material”) gives statistical procedures that can be used to establish equivalency criteria for inclusion in a material specification. Another source for information in this area can be found in DOT/FAA/AR-00/47 and DOT/FAA/AR-03/19.
(3) Any material changes that result (or can be expected to result) in a change to the material allowables, or to the acceptance limits, are considered to be a major processing change.
Equivalency is used to evaluate all changes in a material’s constituents, manufacturing process, or to changes in the fabrication (e.g., curing) process that could potentially require a new material qualification and associated designation. When such potential exists, the equivalency procedures are applied to determine whether a new qualification database is needed to accommodate such change.
(4) DOT/FAA/AR-02/109 provides recommendations for the procedures to evaluate five levels of material changes, which range from minor to major. These recommendations are based on experience and engineering judgment, with additional data collected at higher levels of 14
change to add confidence that the change does not require a new material or process designation.
The discussions give examples, as well as the testing and notification guidelines associated with each level of change. The lower levels of change, which are considered minor, may be evaluated without a full set of equivalency tests. Higher levels of change require an equivalency demonstration and associated updates to the material specification and PCD.
(5) Discussions on the highest level of change in DOT/FAA/AR-02/109 suggest that certain material or process modifications should automatically trigger the development of a new qualification, material designation, and associated specifications. These include changes in resin composition, fiber areal weight, fiber type, and fabric weaves.
e. Quality Assurance. The PCD and material specification establish quality assurance procedures that evaluate requirements. The latter defines the batch-sampling plan for material acceptance and establishes testing responsibilities of the material supplier and purchaser. Key characteristics will be monitored using SPC at the material supplier. “Material acceptance” is the process of determining, by test and/or inspection, whether a specific batch of material meets the requirements of the applicable procurement specification. ("Material acceptance" is also called "quality conformance" in specifications that conform to MIL-STD-490/961 practices.) A subset of the material qualification tests are selected and designated as "acceptance tests." These tests measure key material/process characteristics that are sensitive to a potential change in the material. As discussed previously, statistical methods are used to determine the associated material specification requirements using the qualification data and subsequent production batch data.
(1) Statistical Process Control (SPC).
(a) Modern production practices emphasize SPC tools, which use acceptance testing data and process control tests, to monitor production trends and make real-time process corrections. Each supplier’s site for prepreg manufacturing is qualified by demonstrating the capability to conduct raw material testing, final product testing, maintenance, calibrations, and the continuing practice of SPC methods. Training programs and records help to ensure that personnel are able to perform and document these tasks. Major equipment maintenance and modification records are available. Appropriate organizational structure exists for each major function (i.e., operations and quality assurance) to ensure consistent production practices.
(b) The quality assurance department, at the material supplier, maintains the procedures and requirements for SPC based on key characteristics (KC) and key process parameters (KPP). The KCs are those uncured and cured prepreg material properties that are given as requirements. The KPPs are those process parameters that have a significant influence on the KCs. The KPPs are determined before qualification and documented in the PCD.
Average values, ranges, limits, and sampling frequency are established and documented in the PCD. Procedures used to conduct SPC analysis of the KCs and KPPs are also documented in the PCD. Control charts are maintained on the KCs.
(c) A corrective action is taken whenever the criteria for non-random data trends are met, while the data is still within the upper and lower control limits given in the PCD. If a KC is 15
out of control, the cause of variation is identified and eliminated to re-establish statistical control.
The supplier’s quality assurance department documents all corrective actions affecting the process and monitors whether the corrective action has been effective.
(d) A plan for reduced testing, which is based on the capability of the KCs and KPPs, may be established and documented. The reduced testing may take the form of a reduction of purchaser testing. Reduced testing will require approval by the FAA and the purchaser(s) before being implemented. If KCs are found to be out of control, testing will return to the original level until confidence in the control of the material is re-established.
( 2) Product Certification.
( a) The specification defines the material acceptance testing to be performed by the material supplier and the end user (purchaser). The material supplier performs the material acceptance testing that is identified in the material specification and PCD. Conformance reports are prepared for each prepreg batch to document that the uncured and cured prepreg requirements have been met. The supplier quality department will review these documents before shipment to a purchaser along with the material. All records for each prepreg batch and the original baseline database are kept on permanent file. Records of quality assurance and full prepreg batch traceability are kept for a minimum of 10 years or as required under the applicable production rules.
(b) Materials that fail quality assessment tests undergo a review process. The retest or replacement of test data is allowed if statistical criteria are met to identify data outliers and a physical reason for the outlier is determined. It may also be acceptable if test abnormalities or testing errors can be reasonably deduced, providing steps are taken to eliminate potential future problems. Engineering guidelines in this area are provided in MIL-HDBK-17, DOT/FAA/AR- 00/47 and DOT/FAA/AR-03/19.
(c) The purchaser's quality department performs the acceptance testing identified in the material specification on each prepreg batch received directly from the manufacturer or through a distributor. The quality department must review the test results and allow the prepreg to be released to manufacturing only if the material meets the specification requirements. If an approved system, which controls the material, is in place to release material pending testing, that system may be used. The purchaser holds to the same record keeping requirements and retest criteria as the material supplier. The original conformance reports created by the prepreg manufacturer will be made available by the distributor for a specific batch sold to the end user.
(d) In cases where the SPC has demonstrated a high level of control and capability for the material, it may be possible to either reduce or eliminate the purchase acceptance testing.
The FAA ACO will evaluate requests for reduced purchaser testing on a case-by-case basis. If purchaser testing is reduced or eliminated, then provisions for monitoring the thermal exposure history of each shipment of material between the supplier and end-user (including all transit periods and storage periods at a distributor) will be required.
f. Material Test Methods. The material specification and PCD will clearly reference or document all test methods required for material control. Chapters 3 through 7 in Volume 1 of the MIL-HDBK-17 give recommended composite test methods. When available, international standards (e.g., ASTM International) are preferred. The ASTM International standards designed specifically for advanced composites come from Committee D30. Options in standards (e.g., specimen width) are controlled and any deviations from industry standard methods must be clearly detailed in the specification or PCD. We recommend that the material supplier and purchaser conduct round-robin test evaluations to reduce test differences for methods required by the specification. All laboratories involved in testing are certified to the specified methods. For an industry material specification, we recommend that a third-party organization be used to certify the test laboratories.
g. Test Panel Fabrication. The fabrication processes used to produce test panels for the initial qualification database and subsequent quality assurance tests are clearly defined in the material and process specifications. This includes laminate layup, bagging, cure, quality inspections, and test specimen machining. The material suppliers and end users must be able to perform the baseline cure process on a routine basis. Process aids such as vacuum bag material, vacuum sealant, breathers, caul plates, and edge dams are defined in the PCD and process specification.
h. Packaging and Shipping Requirements.
(1) The prepreg release film or paper used for a material are easily removable, noncontaminating, and controlled by the PCD. Changes to a different release paper include a demonstration that no contaminants are transferred from the paper to the product.
(2) The material product has suitable identification in packages used for shipping. The packaging and handling during shipping are controlled such that the purchaser realizes the material full handling and out life capability when received. If repackaged by a distributor, the new packaging is labeled properly and functionally equivalent to the original packaging. Any decrease in storage life, out life, and handling life are documented by the distributor and provided to all users.
(3) Material identification provides the batch number and roll number on two labels, one inside the core, and the other outside the shipping wrapper. These labels also include the material designation, name of manufacturer, specification number, and date of manufacture.
(4) The prepreg packaging has a core that adequately supports the weight of the roll without deformation. The roll is in a sealed bag that prevents the ingress of moisture and contaminants. Additional packaging, such as a box, may be needed to ensure that the bag is not torn during shipment.
(5) The shipping and storage temperatures are established and documented in the material specification. If freezer temperatures are needed to maintain product quality, recording devices should be used to track the temperature exposure history during shipment. Provisions 17
are needed in the material specification for the disposition of rolls that have exceeded recommended time-temperature limits or are received with damaged packaging.
i. Use of a Distributor in the Supply Chain.
(1) When using a distributor, either a facility of the manufacturer or an independent facility, the distributor abides by all requirements of the material specification and the applicable portions of the process specification. The end user approves the distributor under their supplier surveillance system as described in the quality control manual. The material manufacturer will also have a role in authorizing distributors for proper control of the composite material. Material lots remain traceable to the manufacturer's original batch and test reports. The distributor provides copies of the original material certification and test reports for the user. The manufacturer's material, batch and lot identification are maintained.
(2) A distributor practices the same documentation of storage life and conditions as the material supplier. The distributor provides objective evidence of the material storage conditions.
All shelf life is determined from the date of material production. Any extension of the shelf life allowed by the material specification is performed by a source approved by the original manufacturer.
(3) If the product is repackaged, the materials used to repackage it are approved for use by the manufacturer. When the material is repackaged, it will first be allowed to reach room temperature in the unopened package so moisture does not condense on the prepreg. The repackaged material is inspected for visual defects and documented. All out life accumulated during warming, respooling, and repackaging is subtracted from that specified by the manufacturer and documented for the user, who assumes responsibility after acceptance.
6. PROCESS SPECIFICATION.
a. Overview.
• The material and process specifications are interwoven. The material specification is used to ensure that the delivered aircraft contains materials that meet the same quality and performance standards as those achieved in the certification process. The process specification controls the processes used to convert materials into structural components. The specific processes used for fabrication directly determine the performance properties of composite laminates. The current paragraph gives the regulatory policy for a process specification, with an emphasis on instructions and controls for the processes used in fabricating the test panels important to the quality assurance of prepreg materials. (The terminology “process specification” will be used throughout this AC for the instructions and controls used in test panel fabrication. However, only part of a process specification contains such information, which may alternatively appear in other documentation.)
• The objective of process specifications is to document any regulatory and engineering requirements or procedures that are communicated to organizations involved in the fabrication process. For example, the process specification relates to the fabrication 18
of high quality and consistent composite laminates. Considering the complexity of associated process steps, the specification is clear and complete to meet the objective.
• A process specification is needed to ensure that the fabrication process, which is used for test panels during certification, is stable and consistent. The consistency includes control of thickness, layup, and cured characteristics. While the test panel process is repeatable, it also captures the variations found in the component fabrication process and, therefore, provides an acceptable baseline for future equivalency exercises. As discussed in paragraph 5d of this AC, equivalency tests are used to judge whether production changes are minor or major. Another function of the process specification is to require complete documentation of the process parameters used to fabricate a specific set of test panels so that traceable records exist whenever questions arise.
• Although the current discussion is focused on those parts of a process specification that are important to test panel fabrication, there are significant manufacturing scaling issues for composite airframe structures. These scaling issues can be important to material and process development that includes the procedures for control of raw materials. Some scaled manufacturing demonstrations should be performed at the same time as base material and process specification development so the appropriate controls are defined to ensure producible airframe structures.
(1) Standard Specification Format.
(a) The FAA Technical Report [DOT/FAA/AR-02/110] has compiled the criteria and guidelines that are deemed essential to develop a process specification. This guidance is only applicable to polymer matrix material systems. A standard format for the outline of a process specification can be found in the FAA Technical Report [DOT/FAA/AR-02/110]. This format was derived from SAE International recommendations. As a result, format information contained in the FAA report may be superseded by future change in the SAE International recommended format.
(b) The initial sections of a process specification typically provide general information that is essential to users of the specification. The remaining sections contain the processing instructions, engineering controls, and guidelines. The particular order and names for sections in a given process specification may differ from industry standards; however, similar content is included in process specifications or other related documents used to control composite processes.
( 2) General Information. The general information essential for a process specification includes the following:
(a) Describe the purpose or application of the specification in the front of the document. For example, the purpose would be to give requirements and procedures for the fabrication and inspection of composite laminates. Such a specification would be used to qualify new materials, perform material quality assurance, or establish mechanical property equivalency.
(b) List (usually near the front) all supporting documents, reports, specifications, or standards referenced within the process specification. Also, specify sources for the documents.
(c) Provide definitions, abbreviations, and other relevant information that need to be understood to follow the specification. Wherever possible, use definitions from industry standards.
b. Fabrication Requirements.
(1) Personnel. Technicians are “qualified” for each of the major fabrication processes (layup, bagging, cure, Nondestructive Inspection (NDI), testing, machining) that they perform.
(2) Required Materials.
(a) List all materials (and their sources) required for the fabrication procedures in the process specification. The listing includes both consumable and structural materials. Upon receipt, prepreg materials are inspected per the material specification before use. Verifications exist to ensure that all materials that come in contact with composite prepreg would not cause contamination. Any foreign objects that could potentially become part of the laminate are verified detectable by cured laminate inspection procedures.
(b) Document the total shelf life and out time of prepreg materials up to the time of panel cure. The time limit within which the material will produce quality laminates is a requirement. Throughout this time, the prepreg material storage conditions and working environment (temperature and relative humidity) are controlled per specification requirements.
Maintain complete records to ensure fiber, resin, prepreg, and cured laminates are traceable.
(3) Required Equipment, Facilities and Tooling.
(a) All equipment needed to perform the fabrication procedures, which are documented in the process specification, are listed with vendor sources. Define calibration and certification requirements for all equipment (e.g., ovens, autoclaves and process monitoring gauges).
(b) Perform laminate layup in a clean and controlled environment. The temperature and relative humidity of the layup room are maintained within limits of the out time requirements. Layup areas are cleaned and inspected regularly. Mold releases or other materials that could cause contamination are not allowed into the layup room. Any process steps that generate dirt, dust or other debris are also not allowed in the room (e.g., sanding or machining).
A positive pressure, filtered ventilation system in the layup room is recommended.
(c) All tools used in fabrication are clearly identified and documented in the process specification. Cure tools are designed and validated to yield required panel geometry for the specified process conditions. Tool handling, storage, and maintenance requirements need to be defined to protect tools over time. Any tooling aids to facilitate accurate ply layup and to maintain laminate panel orientation in subsequent process steps are specified. Irons or heat guns used to facilitate ply layup are calibrated to control ply temperature during ply layup.
(4) Required Procedures.
(a) All procedures required to fabricate quality laminates need to be adequately detailed in the process specification to ensure consistency. Create documentation for each panel fabricated, starting with planning instructions and including records of specific materials and actual process parameters used for each fabrication step. Assign an identification number or code to each panel so it is traceable to the associated records. The process specification will have fabrication details for tool preparation, material handling, laminate layup, cure cycle, panel identification, inspection, and machining.
(b) The process specification details the steps needed for tool and raw material preparation. The former includes inspections that verify the tools were properly cleaned and in good working condition. Give procedures for mold release application. Material preparation process steps will start with identification of the specific materials to be used and a review of their associated records. To prevent moisture condensation, specify the procedure to warm frozen prepreg before opening storage containers. To avoid ply damage and contamination, detail prepreg cutting and handling procedures.
(c) In the process specification, detail instructions for laminate layup and panel bagging. Each ply must be accurately oriented and inspected for defects during layup. Debulk groups of plies in a layup sequence with vacuum pressure per specified instructions. Identify and apply specific bagging materials, tooling aids, and thermocouples for cure monitoring according to the detailed steps in the specification.
(d) The process specification includes details for fabricating a panel to the applicable cure cycle. Before cure, perform a leak check on the vacuum bag and take corrective action as needed. The cure cycle should define heat-up rate, temperature range, time, vacuum, pressure, and cool down rate. Develop procedures to monitor cure time and temperature. Keep records of temperature, vacuum, and pressure for the complete cure cycle.
(e) Document step-by-step procedures for inspections and test measurements used to ensure the quality of cured panels in the process specification, along with associated engineering requirements. These procedures, which need to be performed before panel machining, are best started with a review of process records to ensure that panels are fabricated in compliance with requirements. Subsequent efforts determine laminate thickness, layup, panel flatness, surface defects, completeness of cure, and void content. Use nondestructive inspections, which are tied to standards for laminate defects, to detect any embedded flaws that cannot be measured visually.
FAA Technical Report [DOT/FAA/AR-02/110] gives some recommendations on details for the inspections and test measurements, which can be used for the quality assessment of cured laminate panels.
(f) The process specification provides details on machining cured panels. Develop machining diagrams to cut test specimens for each panel and include in the detail processing instructions. Lines drawn on the laminate surface may be used to aid the process. Instructions in the specification should identify the type of machining equipment needed, as well as cutting tool 21
type, speeds, and feed rates. After machining, specimens are inspected for damaged edges and measured for dimensional accuracy per requirements.
c. Quality Assurance.
(1) In the process specification, include quality assurance procedures to monitor the fabrication processes as well as the necessary materials, equipment, facilities, and tooling. Each examination, inspection, or testing task performed for quality assurance is defined with a direct link to the fabrication requirements discussed in paragraph 6b of this AC. Organizations or personnel responsible for quality assurance are properly trained and identified in the specification. Specify process documentation procedures, archive time limits, and test methods.
These requirements may be detailed in the quality manual.
(2) Quality assurance inspections are needed for material records that are compared against requirements before panel cure. These include verification of: (1) storage life, (2) total out life, (3) acceptance test results, (4) use of approved consumable materials, (5) batch numbers,
(6) panel fabrication, (7) specimen preparation, and (8) testing procedures.
(3) Periodic quality assurance inspections are needed to verify equipment, facilities, and tooling requirements. This includes the measurements and calibrations needed to control equipment. The layup room temperature, relative humidity, and cleaning schedule need to be verified through measurements and records. Tools and their storage conditions are inspected.
Take surveys on cure tools to ensure uniform heating during the cure cycle.
7. SUMMARY.
a. This AC has been developed based on FAA and NASA joint efforts that are beyond the AGATE shared database methodology. This AC also establishes the guidance for developing composite material and process specifications that ensures adequate material controls. This AC presents the procedure requirements and technical requirements from regulatory perspectives.
Details on technical guidelines can be referred to in the DOT/FAA Technical Reports listed.
b. Structural certification ensures that acceptable materials and repeatable manufacturing processes are used for all parts that are integrated into the production. Material and process controls are essential prerequisites for a repeatable and safe product. The material and process specifications are interwoven throughout the certification process. Material specifications define the material’s attributes and the qualification tests. Process specifications define and control the processes used for conversion of materials into structural components.
c. The essential contents that need to be documented in material and process specifications are presented with a focus on base material control. These include the engineering criteria and guidelines that ensure a repeatable raw material source. For the material specification, the engineering criteria/guidelines are presented in terms of material requirements, material characterization, changes to qualified materials, quality assurance, test methods, test panel fabrication, and packaging and shipping. For the process specification, the engineering criteria/guidelines are presented for test panel fabrication in terms of requirements (including 22