The ABC's of Composite Repair

Strict adherence to the individual OEM approved data, materials, and processes is imperative.

In selecting a title for this article, I wanted to convey the perception that composite repair is not that difficult, or at least no more difficult than sheet metal repair. To be certain, it requires training, practice, and experience to become truly proficient at producing well-crafted, airworthy composite repairs, but then so too does sheet metal repair. The main difference is that composite repair technology most likely represents a new set of skills, processes, and materials to which most technicians have not been exposed.

Should you make the effort to acquire these skills? I will let you be the judge of that, but consider the following: Boeing, Airbus, Gulfstream, Pilatus, Hawker Beechcraft, Dassault, Bombardier, Cessna, Diamond, Cirrus, (to name a few) all rely on composite materials in primary structural applications. In a paper written by the National Institute of Aviation Research, it is projected that the use of composites in aircraft construction will quadruple over the next 20 years.

This rapid growth in aerospace composites will not be without problems. There is and will continue to be a gap between the manufacturers’ (OEMs) development and production of these aircraft, and the maintenance industry’s ability to maintain them. This gap has two aspects: numbers and technology. There are simply not enough technicians trained and experienced in composite inspection and repair to meet the anticipated needs. New inspection and repair technology skills will need to be acquired by maintenance organizations and personnel. Compounding these issues is the fact that there is very little standardization of repair processes among the manufacturers. To overcome this gap, many OEMs have developed and offer training specific to their types.

While this may satisfy the needs of the OEMs, it does not lead to any standardization of the composite repair process. But upon closer examination, we can place the OEM processes within the framework of a series of sequential tasks, recognizing that each OEM may utilize different procedures for completing the task. I have identified the following tasks in outlining a standard composite repair:

Inspection/damage assessment. Each OEM provides inspection and damage assessment criteria in their publications. For the most part, they are consistent on inspection criteria: visual inspection of the structures followed by a detailed inspection of known or suspected damage. On a glass fiber structure, this may involve paint removal (glass fiber reveals damage well visually), tap testing, or NDT inspections. Known or suspected damage to carbon fiber structures usually requires NDT inspection.

Determine repair authority. What is damaged, where it is damaged, and how large is the damage are all criteria manufacturers use when providing standard repair data in their publications. You will find much variation among them. Some are very generous and some are very restrictive in what repairs the publications authorize, but in all cases, there is a point in which you must contact their engineering department for repair support. You need to know where that point is.

Obtain repair data and materials. Whether you are using standard repair data from the AMM/SRM (Structural Repair Manual) or an OEM engineered repair, you need to fully understand the repair before proceeding. I refer to this as “Getting your head around the repair.” If you do not “see” the finished repair, call the OEM help line for assistance. Use only OEM-approved materials within shelf-life limits for accomplishing the repair.

Removal of paint and damaged material. While it may be necessary to remove paint for assessment purposes, you will now need to remove enough paint to accommodate the repair. I am aware of no OEM that allows the use of chemical strippers for paint removal. Repair data will tell you how much damaged material to remove, but generally less is better.

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