Fiberglass and Composite Damage Repair for the A&P Practical

October 25, 2026 · Primary sources checked October 20, 2026

For Airframe and Powerplant (A&P) practical composite repair, use your O&P (oral and practical) rehearsal to connect damage mapping, clean layup, controlled cure and post-repair inspection.

What does this O&P task evaluate?

Use these Federal Aviation Administration (FAA) Airman Certification Standards (ACS) elements to organize a composite inspection and repair rehearsal.

An individual practical project couples a skill demonstration with two practical questions. You may use all available and applicable reference material for both the skill element and the two practical questions.

Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)c)

Each assigned project receives a pass/fail evaluation. Passing this project requires successful work on the first skill attempt as well as successful answers to both associated questions.

Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)f)

You must complete the project to the required performance standard to pass, and the examiner can find that standard in the downloaded test. Under the FAA Mechanic Test Generator (MTG) FAQ, one practical project cannot be combined with another.

Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)g) · FAA Mechanic Test Generator FAQs, updated May 22, 2023, unnumbered page, PDF 4

The FAA’s sample oral and practical test is designated for practice purposes only.

FAA sample oral and practical test, unnumbered page, PDF 6

FAA-S-ACS-1, printed 22, PDF 27

Our worked sequence uses a fiberglass-faced sandwich-panel repair as the rehearsal example; it does not replace a specific aircraft repair instruction.

Start with the repair manual and material controls

Read the structural repair manual (SRM) to determine repair material, ply count and ply orientation. The handbook notes that its honeycomb core-replacement steps are not a substitution for the aircraft-specific SRM. Do not assume that the repair methods used by one manufacturer apply to another manufacturer.

FAA-H-8083-31B, Airframe, printed 7-28, PDF 365 · FAA-H-8083-31B, Airframe, printed 7-35, PDF 372

• All time and temperature requirements must be met and documented, and the aircraft SRM determines the correct cure cycle.
• With prepreg (a fabric or tape impregnated with resin during manufacturing), let the material thaw completely before opening its sealed moisture-proof bag to prevent moisture contamination.
• Keep records of prepreg time in and out of the freezer; material that exceeds its mechanical life needs to be discarded.
• Protect prepreg from dust, oil, vapors, smoke and other contaminants, and clean the repair area immediately before layup.
• Replace each damaged ply with the same material and orientation or an approved substitute; correct ply orientation and sequence are critical.
• Fiberglass molded mats are not used for structural repair applications, although they could be used for nonstructural applications.

FAA-H-8083-31B, Airframe, printed 7-32, PDF 369 · FAA-H-8083-31B, Airframe, printed 7-25–7-26, PDF 362, 363 · FAA-H-8083-31B, Airframe, printed 7-26–7-27, PDF 363, 364 · FAA-H-8083-31B, Airframe, printed 7-27, PDF 364 · FAA-H-8083-31B, Airframe, printed 7-29, PDF 366 · FAA-H-8083-31B, Airframe, printed 7-40, PDF 377

Protect eyes, lungs and skin before cutting or mixing

Using current maintenance and overhaul publications and procedures is included in the ACS safety appendix. Safety glasses, hearing protection and any other required personal protective equipment (PPE) are examples in the ACS safety precautions.

FAA-S-ACS-1, printed A-3, PDF 67

A disregard for safety will result in a failure and is not tolerated by the ACS. When carrying out a portion would jeopardize safety, the evaluator will ask the applicant to simulate it.

FAA-S-ACS-1, printed A-3, PDF 67

• The handbook warns that advanced composite materials, including prepreg, resin systems, cleaning solvents and adhesives, could be hazardous, and that it is important to use personal protection equipment. The material could be a respiratory irritant or carcinogenic, or another kind of dangerous substance; the Safety Data Sheets (SDS) list the hazardous chemicals in the material system and outline the hazards.
• Read and understand the SDS and handle chemicals, resins and fibers correctly.
• Wear safety glasses at all times, and a face shield when mixing or pouring acids.
• Never wear corrective contact lenses in the shop, even with safety glasses: solvents can melt the lenses and dust can lodge underneath and damage eyes.
• Do not breathe carbon-fiber dust, always maintain good airflow at the work, and use a vacuum near the dust source.
• Always use breathing-assistance equipment when working in a confined space.
• Sanding requires a dust mask or respirator, and paint application requires a sealed respirator with the correct filters or a fresh-air-supply respirator.
• Downdraft tables should be monitored and their filters changed regularly to maintain protection and particulate collection.
• Chemicals could remain on your hands and burn sensitive skin. Always wear gloves and clothing that offer protection against toxic materials, and use only approved gloves that protect skin and do not contaminate the composite material.
• Wash your hands before eating or using the toilet, and handle damaged composites carefully because single fibers can penetrate and lodge in skin.
• Most solvents are flammable. Close all solvent containers and store them in a fireproof cabinet when not in use, and keep solvents away from areas where static electricity can occur; static electricity can occur during sanding or when bagging material is unrolled.
• Air-driven tools are preferable; electric tools, when used, must be the enclosed type.
• Do not mix excessive resin because the exothermic reaction could overheat it and start smoking, and ensure a fire extinguisher is always nearby.
• Smoke from overheated quick-curing resin can burn or poison you; mix only the required amount and use more batches rather than exceeding the maximum batch size.
• Always wear safety glasses and other protective equipment when using tools, and do not cut other materials on composite-dedicated equipment because of contamination.

FAA-H-8083-31B, Airframe, printed 7-52, PDF 389 · FAA-H-8083-31B, Airframe, printed 7-53, PDF 390 · FAA-H-8083-31B, Airframe, printed 7-29, PDF 366

A waterjet cutter cannot be used on honeycomb structure because it introduces water into the part.

FAA-H-8083-31B, Airframe, printed 7-52, PDF 389

Map the damage and understand the tap-test limits

Visual inspection can reveal scorches, stains, dents, penetrations, abrasions and chips, but cannot find internal flaws such as delaminations, disbonds and matrix crazing.

FAA-H-8083-31B, Airframe, printed 7-15, PDF 352

• Tap the area with a solid round disc or lightweight hammer-like device and listen to the structure’s response.
• A clear, sharp ring indicates well-bonded solid structure; a dull or thud-like response indicates a discrepant area.
• Changes in internal construction can alter pitch and be mistaken for defects.
• Tap inspection should be done in as quiet an area as possible by experienced personnel familiar with the part’s internal configuration.
• The handbook says this tap method is not reliable for structures with more than four plies.
• Tap testing is not useful for resin cracks or broken fibers and becomes less reliable as delamination depth increases.
• Thicker laminates need more in-depth nondestructive inspection (NDI), such as ultrasound, and the damage vicinity needs checks for water, oil, fuel, dirt or other foreign matter.

FAA-H-8083-31B, Airframe, printed 7-15, PDF 352 · FAA-H-8083-31B, Airframe, printed 7-38, PDF 375 · FAA-H-8083-31B, Airframe, printed 7-35, PDF 372

Clean up the damage and prepare the repair

• Remove water from honeycomb core before repair: otherwise it boils during elevated-temperature cure and blows the face sheets off the core.
• Trapped core water could also freeze at altitude and disbond the face sheets.
• Trim the face-sheet damage to a smooth shape with rounded corners, or a circular or oval shape, without damaging sound plies, core or surrounding material.
• Where core is damaged too, trim it to the skin outline and prepare the surrounding taper using the applicable repair dimensions.
• Remove sanding dust with dry compressed air and a vacuum cleaner, then clean with a clean cloth moistened with approved solvent.
• The replacement core plug must have the original core’s type, class and grade, and its cells should align with the surrounding honeycomb.
• For the handbook’s wet-layup core replacement, impregnate the two inside fabric plies with resin, place them in the hole and install the plug with potting compound around it.
• Vacuum bag the repair area, cure the core replacement in an oven, in an autoclave or under a heat blanket (usually on a separate cycle from the patch), and sand the cured plug flush with the surrounding area.
• The repair manual controls repair material and ply count, and repair-ply orientation must match the original plies.

FAA-H-8083-31B, Airframe, printed 7-35, PDF 372 · FAA-H-8083-31B, Airframe, printed 7-36, PDF 373

Lay up, vacuum bag and cure to the specified cycle

• Multipart epoxy resins must be thoroughly mixed; scrape the mixing-cup edges and bottom to incorporate all resin.
• Because many resin systems have no dye to show how well they are mixed, the handbook says the resin must be mixed slowly and fully for three minutes; mixing too fast lets air into the mixture, and resin that is not fully mixed may not cure properly.
• For wet layup, impregnate the plies with resin; for prepreg, remove its backing before placing the repair plies.
• Too much or too little resin affects repair strength, and air left in the fabric or introduced into resin reduces it.
• Always consult the maintenance manual or manufacturer technical sheets for the correct bagging and bleeding technique.
• Too many bleeder plies can create a resin-starved repair; no-bleed prepreg loses required resin if allowed to bleed.
• Vacuum bagging removes air and applies pressure to the repair during cure.
• Monitor part temperature with thermocouples because oven or autoclave air temperature is not always a reliable measure of the part’s cure temperature.
• Make sure autoclave pressure is relieved before opening its door. For higher-temperature, higher-pressure cure cycles, the handbook says a 50/50 mix of air and nitrogen or 100 percent nitrogen should be used to reduce the chance of an autoclave fire.
• Our rehearsal record: identify the SRM cycle, bagging stack and temperature-monitoring arrangement before starting; record the required time, temperature and pressure evidence.

FAA-H-8083-31B, Airframe, printed 7-29, PDF 366 · FAA-H-8083-31B, Airframe, printed 7-36, PDF 373 · FAA-H-8083-31B, Airframe, printed 7-28, PDF 365 · FAA-H-8083-31B, Airframe, printed 7-33, PDF 370 · FAA-H-8083-31B, Airframe, printed 7-22, PDF 359

Inspect the cured repair and restore the finish

• After cure, remove the bagging materials and inspect for pits, blisters, resin-rich areas and resin-starved areas, which the repair should be free of.
• Light sanding should smooth the patch without damaging fibers; apply the top finish and conductive lightning-protection coating.
• Inspect the repair visually, by tap and/or ultrasound, and remove the repair patch if defects are found.
• After repairing a flight control, perform a balance check and ensure SRM limits are met; failure could cause flutter and affect flight safety.

FAA-H-8083-31B, Airframe, printed 7-37, PDF 374

Common repair-rehearsal mistakes

• Our checklist: do not use a tap sound as proof of every internal condition, choose a generic ply count, leave moisture in the core, or treat a cured-looking surface as evidence that the cycle was correct.
• Room-temperature-cure wet-layup repairs do not restore either the strength or the durability of original components cured at 250 °F or 350 °F; they are often used for wet-layup fiberglass repairs of noncritical components.

FAA-H-8083-31B, Airframe, printed 7-32, PDF 369

For examiner fees and planning, read the DME exam cost guide.

Related guides

• Non-Metallic Structures Oral Exam Questions and Answers
• Sheet Metal Structures Oral Exam Questions and Answers
• A&P Practical Projects: What the DME Evaluates on the O&P

Sources

Primary sources checked October 20, 2026.

• FAA-S-ACS-1
• FAA-H-8083-31B, Airframe
• FAA Mechanic Test Generator FAQs, updated May 22, 2023
• Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929
• FAA sample oral and practical test

About this guide: drafted with AI from the FAA sources listed on this page and checked claim by claim against them. Not reviewed by an A&P mechanic or DME. How we make our guides