Subject: Acceptance Guidance on Material

Procurement and Process Specifications for 

Polymer Matrix Composite Systems 

Date: 9/19/03

Initiated By: ACE-100

AC No: 23-20

Change: 

CONTENTS

Paragraph Page

1. PURPOSE............................................................................................................. 1 

2. RELATED REGULATIONS AND GUIDANCE DOCUMENTS...................... 1 

a. Regulations...................................................................................................... 1 

b. Advisory Circulars.......................................................................................... 2 

c. Policy Statements............................................................................................ 3 

3. SUPPORTING REFERENCES............................................................................ 3 

a. DOT/FAA Technical Reports......................................................................... 3 

b. Industry Standards .......................................................................................... 4 

4. BACKGROUND .................................................................................................. 4 

a. Scope ............................................................................................................... 4 

b. Historical Perspectives.................................................................................... 4 

c. Shared Databases ............................................................................................ 5 

d. Material Qualification & Equivalency (MQ&E)............................................ 5 

e. Material Control.............................................................................................. 6 

f. Importance to Structural Substantiation .......................................................... 7 
AC 23-20 9/19/03 

5. MATERIAL SPECIFICATION .......................................................................... 8 

a. Overview......................................................................................................... 8 

b. Material Requirements.................................................................................... 9 

c. Material Characterization.............................................................................. 12 

d. Changes to Qualified Materials .................................................................... 14 

e. Quality Assurance ......................................................................................... 15 

f. Material Test Methods................................................................................... 17 

g. Test Panel Fabrication................................................................................... 17 

h. Packaging and Shipping Requirements ........................................................ 17 

i. Use of a Distributor in the Supply Chain....................................................... 18 

6. PROCESS SPECIFICATION............................................................................. 18 

a. Overview....................................................................................................... 18 

b. Fabrication Requirements............................................................................. 20 

c. Quality Assurance ......................................................................................... 22 

7. SUMMARY........................................................................................................ 22 

8. FUTURE STANDARDIZATION...................................................................... 23 

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9/19/03 AC 23-20 

1. PURPOSE. 

a. This advisory circular (AC) provides information and guidance concerning an 

acceptable means, but not the only means, of compliance with Title 14 of the Code of Federal 

Regulations (14 CFR) part 23. It is applicable to the material and process specifications, or 

other documents, used to ensure sufficient control of composite prepreg materials in normal, 

utility, acrobatic, and commuter category airplanes. Material in this AC is neither mandatory 

nor regulatory in nature and does not constitute a regulation. 

b. This AC has been developed with the help of industry to ensure adequate composite 

material control and to promote standardization of material and process specifications. It 

presents the procedural requirements and technical information from a regulatory 

perspective. Readers interested in engineering guidelines and recommended criteria should 

refer to the DOT/FAA Technical Reports provided under the Supporting References in 

paragraph 3. 

c. This AC is issued for guidance purposes and to outline a method of compliance with 

applicable airworthiness requirements. Because the method of compliance presented in this 

AC is not mandatory, the terms "should" and "must" used in this AC apply only to an 

applicant who chooses to follow this particular method. 

2. RELATED REGULATIONS AND GUIDANCE DOCUMENTS. 

a. Regulations. This AC provides guidance for showing compliance with 14 CFR part 

23 requirements relating to material control. The regulations that are directly related to this 

AC include the following: 

• Section 23.601 General 

• Section 23.603 Materials and workmanship 

• Section 23.605 Fabrication and methods 

• Section 23.613 Material strength properties and design values 

(1) Section 23.605 requires that "the methods of fabrication used must produce 

consistently sound structure." Furthermore, "if a fabrication process requires close control to 

reach this objective, the process must be performed under an approved process specification." 

This rule mandates that each new aircraft fabrication method be substantiated by a test program. 

(2) Section 23.613 contains specific requirements for material strength properties and 

design values. The requirements that are particularly relevant to this AC include the following: 

• "Material strength properties must be based on enough tests of material meeting 

specifications to establish design values on a statistical basis." [§ 23.613(a)] 

• "Design values must be chosen to minimize the probability of structural failure

due to material variability." [§ 23.613(b)] 

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AC 23-20 9/19/03 

• "The effect of temperature on allowable stresses used for design in an essential 

component or structure must be considered where thermal effects are significant 

under normal operating conditions." [§ 23.613(c)] Section 23.603(a)(3) 

prescribes similar requirements. 

(3) This AC focuses on ensuring the control of composite material systems. It closely 

ties to a policy statement titled “Material Qualification and Equivalency for Polymer Matrix 

Composite Material Systems” issued by the Small Airplane Directorate. 

b. Advisory Circulars. Obtain the ACs listed below from the U.S. Department of

Transportation, Subsequent Distribution Office, Ardmore East Business Center, 3341 Q 75th

Avenue, Landover, MD 20785. The following two Federal Aviation Administration (FAA) ACs 

present recommendations for showing compliance with FAA regulations associated with 

composite materials: 

 • AC 20-107A Composite Aircraft Structure 

• AC 21-26 Quality Control for the Manufacture of Composite Structures

(1) AC 20-107A sets forth an acceptable means, but not the only means, of showing 

compliance with the provisions of 14 CFR parts 23, 25, 27, and 29 regarding airworthiness type 

certification requirements for composite aircraft structures. Paragraphs 5 and 6 of AC 20-107A 

contain valuable guidance relevant to this AC, including the following: 

• Material design values, or allowables, which have a high degree of confidence 

based on experimental evidence, in the appropriate critical environmental 

exposures expected in service. 

• Material and processing variability considerations in deriving proper allowables 

or design values for use in analysis, and in the analysis of the results of supporting 

tests. 

 

(2) AC 20-107A also presents guidance on associated quality control and production 

specifications. It states that specifications covering material, material processing, and fabrication 

procedures should be developed to ensure a basis for fabricating reproducible and reliable 

structure. 

 

(3) AC 21-26 provides guidance on 14 CFR part 21 regarding quality control systems for 

the manufacture of composite structures involving fiber reinforced materials. It also provides 

guidance on the essential features of quality control systems for composites. 

(4) Paragraph 5 of AC 21-26 recognizes that the material properties of a composite 

structure are manufactured into the structure as part of the fabrication process. Material and 

process specifications used to produce composite structures must contain sufficient information 

to ensure that critical parameters in the fabrication process are controlled in production. It also 

provides information on elements that are to be contained in a typical material and process 

specification. Furthermore, paragraphs 7 and 8 of AC 21-26 provide an additional description of

the requirements relating to both aspects of material and manufacturing controls. 

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9/19/03 AC 23-20 

c. Policy Statements. The Small Airplane Directorate issued two policy statements that 

contain information that ties or closely pertains to the contents of this AC. They are the 

following: 

• “Material Qualification and Equivalency for Polymer Matrix Composite Material

Systems" [PS-ACE100-2002-006, September 2003] 

• "Static Strength Substantiation of Composite Airplane Structure" 

[PS-ACE100-2001-006, December 2001] 

(1) The first policy statement presents some of the procedures and technical 

requirements associated with elements of material qualification, equivalency, and continuous 

quality control. Technical details are referred to in the FAA Technical Reports (DOT/FAA/AR00/47 in 2001 and DOT/FAA/AR-03/19 in 2003, see paragraph 3a of this AC). 

(2) The policy statement on "Static Strength Substantiation" addresses the composite 

structural substantiation. It includes higher levels of evaluation to substantiate design-specific 

detail at structural scales. 

(3) The two policy statements listed above discuss the connection/application of the base 

material database established by the qualification testing for fulfilling the higher-level structural 

substantiation. 

3. SUPPORTING REFERENCES. 

a. DOT/FAA Technical Reports. The following technical reports are published by the 

FAA Technical Center and are available to the U.S. public through the National Technical 

Information Service (NTIS), Springfield, Virginia 22161. They are also available at the FAA 

William J. Hughes Technical Center's Full-Text Technical Reports page: actlibrary.tc.faa.gov in 

Adobe Acrobat portable document format (PDF). 

• “Material Qualification and Equivalency for Polymer Matrix Composite Material

Systems" [DOT/FAA/AR-00/47, April 2001] 

• “Guidelines and Recommended Criteria for the Development of a Material 

Specification for Carbon Fiber/Epoxy Unidirectional Prepregs" [DOT/FAA/AR02/109, March 2003] 

• “Guidelines for the Development of Process Specifications, Instructions, and Controls 

for the Fabrication of Fiber-Reinforced Polymer Composites" [DOT/FAA/AR02/110, March 2003] 

• “Material Qualification and Equivalency for Polymer Matrix Composite Material

Systems: Updated Procedure" [DOT/FAA/AR-03/19, September 2003] 

(1) The Technical Report on material qualification and equivalency (MQ&E) presents 

details developed under the Advanced General Aviation Transport Experiments (AGATE) 

program. This method enables an airframe manufacturer to qualify composite material systems 

by sample testing to share a central material qualification database. 

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AC 23-20 9/19/03 

(2) The information contained in the other two technical reports provides guidelines for 

material and process control, which is a logical advancement of the AGATE method. The FAA 

and National Aeronautics and Space Administration (NASA) worked jointly with industry 

experts to collect inputs on key properties that need to be controlled to ensure stable composite 

materials. The criteria/guidance presented in these two reports, which are applicable to part 23 

products, form the core contents of this AC. 

b. Industry Standards. MIL-HDBK-17 (current version) has been developed with the help 

of industry and is maintained as a joint effort of the Department of Defense (DOD) and the FAA. 

(At the time that this AC was first released, Version F of MIL-HDBK-17 was current.) The 

handbook provides guidance for developing base material properties (allowables) and the design 

values acceptable to the FAA. Valuable information closely related to this AC is contained 

under Chapter 2 in Volume 1 of this handbook (i.e., Guidelines for Property Testing of 

Composites). MIL-HDBK-17 can also serve as a reference for most of the terminology used in 

this document. MIL-HDBK-17 can be obtained from the Department of Defense Single Stock 

Point (DODSSP), 700 Robbins Avenue, Building 4D, Philadelphia, PA 19111. This handbook 

can also be purchased through ASTM International's website at "www.astm.org" [note: search 

using keyword "MIL-17"]. 

 

(1) The material and process specifications normally refer to industry test methods or 

standards such as American Society for Testing and Materials (ASTM International). These 

standards are available through ASTM at either their Internet site address, which is 

"www.astm.org", or their mailing address: ASTM International, 100 Barr Harbor Drive, PO Box 

C700, West Conshohocken, Pennsylvania 19428-2959. 

(2) Consistent and repeatable industry engineering practices would help assure 

compliance with the requirements for material control. The purpose of building on the current 

FAA/NASA effort is to standardize these specifications with MIL-HDBK-17, ASTM 

International, and Society of Automotive Engineering (SAE International) Aerospace Materials 

Specifications (AMS) Committee P-17. 

 

4. BACKGROUND. 

a. Scope. The guidance in this document pertains to prepreg materials, but many of the 

basic concepts are generic for composite material control. It was derived from certification 

experiences with the help of industry groups, which represent composite material suppliers and 

manufacturers for small airplanes (part 23), transport airplanes (part 25), and rotorcraft (parts 27 

and 29) product categories. Future efforts to continue development of reliable industry standards 

for the control and testing of composite materials are needed. The FAA supports international 

initiatives in this area. 

b. Historical Perspectives. Composite materials have not achieved the same level of 

standardization as metallic materials. This includes a general lack of industry material and 

process specifications and shared databases for basic properties, as well as test standards that

continue to evolve. Composite manufacturers must face these issues as they establish the 

necessary base material control to ensure repeatable production of their aircraft product. Such 

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9/19/03 AC 23-20 

control must be achieved in the quality assurance procedures developed by each user and their 

selected material suppliers. 

(1) In the decades since the introduction of advanced composite materials for use in 

aircraft, the cost associated with material control has been a significant burden to the industry. 

The cost burden begins with the need to conduct qualification testing for each material system to 

be used by an airframe manufacturer. The cost may be further escalated by instabilities 

originating from the sources associated with material supply. Examples of instabilities may 

include changes in material and/or process from the supplier end and, on a larger scale, the 

reshaping of the supplier industry as new users and markets evolve. 

(2) Traditionally, each manufacturer conducted extensive qualification testing to develop 

the base material properties and allowable strengths, which are part of their aircraft design data. 

The practice of qualification, when performed by each manufacturer for an identical material 

system, represents a duplication of effort. The same can be stated for development of those 

portions of the composite material and process specifications used to control the source of raw 

materials.

c. Shared Databases. In recent years, NASA, the FAA, and industry worked together 

through the AGATE program to develop a cost-effective method of qualifying composite 

material systems and sharing a central material qualification database. This method is built on 

existing sections of MIL-HDBK-17, and it allows credit for FAA approved materials testing 

performed by third parties such as material suppliers. 

(1) To use an approved composite material system, airframe manufacturers need to 

perform a smaller subset of testing (i.e., equivalency) to substantiate their control of material and 

fabrication processes tailored to a specific application. Throughout its development, the FAA 

closely participated in the AGATE program to ensure that this method is in compliance with the 

applicable airworthiness regulations. Use of the shared database presents not only a significant 

cost saving opportunity for airframe manufacturers, it also provides the stability needed in the 

material suppliers environment. 

(2) Two FAA Technical Reports [DOT/FAA/AR-00/47 and DOT/FAA/AR-03/19] have 

been published to present the technical details of the AGATE method. Based on this AGATE 

method, the Small Airplane Directorate issued a policy statement titled "Material Qualification 

and Equivalency for Polymer Matrix Composite Material Systems." This policy statement 

presents both the procedure and the technical requirements associated with this method. Since 

the proposed version was issued, in May 2000, several workshops and presentations have been 

conducted for audiences representing the authorities and the industries, both domestic and 

foreign. The AGATE method made a big step in achieving the objective of stabilizing the 

composite materials, while enhancing efficacy both in terms of cost and cycle time. 

d. Material Qualification & Equivalency (MQ&E). A review of the AGATE method 

provides a clear purpose for material qualification and equivalency. Material qualification is a 

process of establishing the database to control an "original" material system. The qualification 

 5 
AC 23-20 9/19/03 

method documented by AGATE presents guidelines for base material properties with several 

purposes: 

• To solidify and finalize material and process specifications, including specific 

acceptance criteria for sampling relative to the qualification database; 

• To quantify base material variability; and 

• To provide a central database of material properties for stable processes. 

(1) Material equivalency is a process to substantiate material properties. (See paragraph 

5d of this AC for expanded discussion.) This is achieved by test sampling and passing the 

acceptance criteria, which were derived from a larger population of material data. The 

equivalency method documented by AGATE presents guidelines for engineering practices with 

several purposes: 

• To share and make use of the central database by a new user (i.e., original 

material qualification); 

• To continue surveillance of material and process; 

• To show that minor changes to material and processes do not affect base material 

properties; and 

• To make final adjustment on material and process specifications for specific 

application, and demonstrate that it has minor effect on base material properties. 

(2) The AGATE MQ&E protocol for shared databases provides a basis in consistent 

engineering practices for composite material control. Following this basis, fundamental 

requirements for material control should include the following: 

• Qualification database should be the statistical basis for equivalency (for new 

users and changes) and quality control acceptance requirements; 

• Documentation and databases should exist for each unique material; and 

• Property drift should be minimized. 

e. Material Control. The FAA and NASA performed efforts, which go beyond AGATE, in 

composite material control. The primary purpose of these expanded efforts was to establish the 

guidance for developing composite material and process specifications. Shared composite 

databases and specifications throughout industry would improve the efficiency of material 

suppliers, end-users, and regulators. 

(1) The FAA/NASA work was administered through the FAA Technical Center and 

Airworthiness Assurance Center of Excellence (AACE) at Wichita State University (WSU). 

Industry experts that have extensive experience with material specifications, part processing, 

qualification programs, and design allowables were invited to participate. They worked together 

in drafting detailed guidelines for material control. This task covers product categories of small 

airplanes (part 23), transport airplanes (part 25), and rotorcraft (parts 27 and 29). In August 

2002, a workshop was conducted in Chicago that provided a forum for experts, both from

government and industry, to discuss the most efficient ways to achieve composite material 

control. 

6 
9/19/03 AC 23-20 

(2) The inputs generated through the FAA/NASA/industry joint effort have been 

compiled and published in two DOT/FAA Technical Reports. This effort was driven by the 

following goals: 

• Greatly reduce the number of material and process specifications for identical 

composite material systems; 

• Develop property databases that uniquely define a given material; 

• Establish material batch testing and process monitoring sufficient to minimize 

variability and preclude property changes over time; and 

• Reduce costs through common documentation and shared databases of basic 

material properties.

f. Importance to Structural Substantiation. Analysis and base material data alone is 

generally not adequate for substantiation of composite structural designs. The "building-block 

approach" is typically used to fulfill the certification requirement. While details of the "buildingblock approach" appear in MIL-HDBK-17, the portion that pertains to part 23 certification has 

been discussed in two policy statements issued by the Small Airplane Directorate. 

(1) The AGATE method is typically used to develop the design database and meet 

certification requirements at the lower level of structural complexity (i.e., coupon tests). The 

material qualification testing provides a means for quantitative assessment of the variability of

key base material properties, leading to various statistics that are used to establish material

acceptance, equivalence, quality control, and design basis. 

(2) Structural certification is used to ensure acceptable materials and repeatable 

manufacturing processes are used for all parts that are integrated into the production. The 

material and process controls are essential prerequisites for a repeatable and safe product. 

Material and process specifications are interwoven throughout the certification process. Material 

specifications define the material’s attributes and define the qualification tests. Subsequently, 

materials used for production are purchased under the material specification. 

(3) Aircraft manufacturers use the material specification to ensure that the delivered 

aircraft consists of materials that are of the same quality and performance standards achieved in 

the certification process. Process specifications define and control the processes used to convert 

materials into structural components. The base material properties of composite laminates are 

directly determined by the specific processes used for their fabrication. Quality control 

procedures, which often make use of the lower levels of building block tests, ensure the material 

used to fabricate production aircraft parts remains invariant. 

(4) Building on the base material database, tests at higher levels of the scale (i.e., 

structural laminate, element and sub-component) are typically needed to fulfill the remaining 

parts of the structural substantiation requirement. Structural laminate data may be shared 

between applications and can become part of a central database. As the program moves closer to 

application-specific design detail, data sharing typically becomes more difficult. 

 7 
AC 23-20 9/19/03 

5. MATERIAL SPECIFICATION. 

a. Overview. 

• The qualification of databases and specifications are recognized as the prerequisites 

to ensure a stable raw material source for aircraft products. Detailed background and 

policy for material qualification, shared databases, and equivalency testing of 

polymer matrix composites have been published. 

• A recent joint FAA/NASA effort defined criteria and guidelines for the related 

specifications for effective material control. These criteria and guidelines have been 

published in two FAA Technical Reports. One report focuses on material 

specification [i.e., DOT/FAA/AR-02/109], and the other one focuses on related 

process instructions and controls [i.e., DOT/FAA/AR-02/110]. This paragraph gives 

regulatory guidance on the former. 

• Composite material and process specifications are closely interrelated. A material 

specification typically defines the composite material and its qualification tests. 

Many of the tests require specimens fabricated using the process specification. Once 

qualification is completed, requirements in the material specification are finalized. 

The material specification is used to procure the production material and maintain 

levels of quality attained at certification. 

 (1) Standard Specification Format. 

 (a) The FAA Technical Report [DOT/FAA/AR-02/109] contains the essential criteria 

and guidelines to develop a material specification. This guidance is applicable to polymer matrix 

material systems. It also contains some technical details that only apply to a particular material 

form (unidirectional prepregs). 

(b) A standard format for the outline of a material specification can be found in the 

FAA Technical Report [DOT/FAA/AR-02/109]. This format was derived from SAE 

International recommendations. As a result, format information contained in the FAA report 

may be superseded by future changes in the SAE International recommended format. 

(c) Initial sections of a material specification typically provide general information, 

which is essential to users of the specification. The remaining sections contain the engineering 

criteria and guidelines. The particular order and names for sections in a given material 

specification may differ from industry standards; however, similar content should be included in 

material or other specifications and related documents used to control materials. 

(2) General Information. The general information essential for a material specification 

includes the following: 

(a) Describe all materials controlled by a specification in the front of the document. 

This should include details that define the materials (e.g., form, resin content, cured ply 

thickness, fiber, areal weight, and fiber type) and cure conditions needed for processing, as well 

as a general description of applications and environmental use limits. 

8 
9/19/03 AC 23-20 

(b) List (usually near the front) all references applicable to the specification. These 

may include drawings, specifications, standards, company-specific test procedures and methods 

used in following the specification. Standard methods and procedures available to the public and 

developed or approved by industry organizations are desirable, but they are not required. 

(c) Provide definitions for terms or abbreviations that need to be understood to 

follow the specification. Any terms essential to raw material control (e.g., prepreg allowed 

defect levels) and processing (e.g., storage life and out life) need to be clearly defined with no 

room for interpretation. Where possible, use definitions from industry standards. 

b. Material Requirements. The requirements used to control materials need to be well 

documented. Some requirements will only appear in documents that are proprietary to suppliers 

while other requirements are also documented in the material specification.

(1) Process Control Document. 

 (a) The material supplier establishes a process control document (PCD) or 

equivalent, which contains a description of all the critical details that are used to ensure 

repeatable raw material fabrication. Usually, a PCD is proprietary to the material supplier, who 

is responsible for its maintenance. The PCD is referenced by the material specification. The 

PCD contains more details on raw material processes than potential users need to know; 

however, customers usually review the information to assess material quality assurance. 

(b) The PCD lists all critical raw material ingredients and the associated suppliers. 

All resin components and their manufacturers are listed, including multiple sources. The resin 

component specifications, quality sampling plan, and test methods for properties are referenced 

in the PCD. The fiber specification, quality sampling plan, and test methods for fiber properties 

are also referenced in the PCD. Backing paper and film is controlled like any other critical raw 

material.

(c) The PCD defines key process parameters and establishes statistical process 

control (SPC) procedures. The PCD will contain the requirements for ingredients (fiber, resin, 

and material form), uncured prepreg, and cured prepreg. The process limits, requirements, and 

continuous inspection procedures are given in the PCD and/or specification. Internal documents 

such as company-specific test procedures that are used for material control are referenced in the 

specification and included in the PCD. 

 (2) Prepreg Ingredient and Process Requirements. 

 (a) The material specification includes requirements that define specific raw 

constituents (i.e., resin and fiber). There is only one resin formulation and a single fiber class 

(i.e., specific fiber type, manufacturer, and facility) associated with the unique set of 

requirements. A designation that represents one combination of ingredients and a single mixing 

process is given to the resin. Multiple sources of the same resin ingredient must be validated 

through chemical and physical evaluations. Fiber used in the prepreg is purchased to a separate 

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AC 23-20 9/19/03 

fiber material specification. If multiple fiber sources are included in the specification, then the 

specific prepreg materials that use each fiber type should have a unique specification, prepreg 

designation (i.e., class), and associated prepreg requirements. The fiber sizing, process to add 

sizing, and sizing content are considered to be an integral part of the fiber. 

(b) Resin composition and all steps in the mixing process need to be defined before 

qualification. This includes tolerance limits that are validated by chemical and physical testing. 

Resin ingredients can be blended as long as individual storage and handling requirements are 

met. Chemical and physical testing is used to validate any blending of mixed resin batches. The 

goal is to ensure that all variations in the resin composition and mixing process steps, which are 

within specified limits, yield repeatable resin to produce a consistent prepreg. 

(c) Details for resin mixing steps are defined in the PCD with specific requirements 

that control these processes. Key attributes of the final mix or any pre-mixes are documented as 

requirements. These include gel time, viscosity, and a chemical analytical signature. The resin 

cure kinetics and rheology are also well characterized for limits allowed within the mixing 

processes. A summary of the resin property data, which can be used as requirements to control 

the resin processes, is given in DOT/FAA/AR-02/109. This table also gives some cured resin 

properties (moisture diffusion and resistance to thermal micro cracking), which may be of 

interest to users. 

(d) Fiber requirements are documented. The material specification includes 

requirements that define the specific mechanical and physical properties of the fiber, including 

tensile strength, tensile modulus, and density. The specification also identifies the fiber form and 

tow count. Key fiber properties are listed in DOT/FAA/AR-02/109. 

(e) Fiber storage and handling instructions normally appear in the PCD. A shelf life 

requirement for the fiber sizing is recognized in the processes if the sizing ages during storage. 

Fiber batch blending is allowed in production, providing each fiber batch can be traced. 

(f) The material specification includes requirements that define the processes for 

producing the prepreg. Details of the resin filming and prepreg processes are documented in the 

PCD. Process conditions have maximum and minimum limits that are monitored with the SPC 

procedures. Resin filming process limits maintain the chemical signature while ensuring film

quality (e.g., film thickness and visual characteristics). The prepreg process achieves a 

consistent thickness while controlling resin advancement, degree of impregnation, handling 

characteristics, defects, and fiber/resin distribution. 

(g) Proof is needed that prepreg manufactured at the minimum and maximum limits 

of allowed thermal history could still be processed within limits of the recommended baseline 

cure cycle. This effort is needed to ensure an acceptable baseline cure cycle for cured prepreg 

requirements (see paragraph 5b(4) of this AC). Cured prepreg mechanical property tests in a 

hot/wet condition and an assessment of the degree of cure provide the necessary validation. 

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9/19/03 AC 23-20 

 (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 

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AC 23-20 9/19/03 

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 

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9/19/03 AC 23-20 

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. 

 13 
AC 23-20 9/19/03 

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

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9/19/03 AC 23-20 

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 

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AC 23-20 9/19/03 

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/AR00/47 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. 

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9/19/03 AC 23-20 

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 
AC 23-20 9/19/03 

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 

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9/19/03 AC 23-20 

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. 

 19 
AC 23-20 9/19/03 

(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. 

20 
9/19/03 AC 23-20 

(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 
AC 23-20 9/19/03 

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 

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9/19/03 AC 23-20 

personnel, materials, equipment, facilities, tooling, and procedures) and quality assurance 

(including responsibility for inspection, documentation, and test methods). 

8. FUTURE STANDARDIZATION. 

a. Consistent and repeatable industry engineering practices would benefit the compliance 

with requirements for material control. Shared composite databases and specifications 

throughout industry would enhance the efficiency of material suppliers, end-users, and 

regulators. We are building on the current FAA/NASA effort to pursue standardization of these 

specifications with organizations, including MIL-HDBK-17, the SAE International AMS 

Committee P-17, and ASTM International. 

b. The material contained in this document provides guidance for the current industry and is 

valid for the future standardization efforts in material control. Progress in standardization can be 

tracked at MIL-HDBK-17 meetings (or via the website of "www.mil17.org") as part of active 

FAA initiatives to work with industry to ensure safe and consistent use of composites. 

Michael Gallagher 

Manager, Small Airplane Directorate 

Aircraft Certification Service 

 23