Composites: Tips for working on Cirrus composite structures

There are some differences to be aware of when working on Cirrus aircraft.

Secondary bond damage

This is when disbonding occurs between two pre-cured components. This could be structural or non-structural in nature.

Solid laminate damage

This is structural or non-structural damage which extends beneath the surface protection and affects the solid laminate structure underneath. This could be either penetrating or non-penetrating.

Penetrating. This includes fractures and penetration through the laminate.

Non-penetrating. This includes abrasions, delaminations, surface impact, or gouges through one laminate surface.

Sandwich structure damage

As the name implies, this is damage to composite sandwich structures.

Laminate only. This is damage to only one side of the sandwich structure with no core damage. This type of damage to the sandwich structure can be identified using the solid laminate damage classifications.

Laminate and core. This is when there is damage to one side of the sandwich construction with damage to the core. There is no damage to the opposite laminate surface.

Sandwich penetration. This is damage to both sides of sandwich construction. Both laminate surfaces are punctured and foam core is exposed.

Repair classification

Now that we know what type of damage we have, we need to determine what type of repair we are looking at. Cirrus breaks repairs down into four categories: cosmetic repair, minor repair, major repair, and restricted repair.

Cosmetic repair. Cirrus classifies a cosmetic repair as that which is designed to repair localized surface defects to the original profile and to prevent UV damage and moisture ingress. Cosmetic repairs relate to minor defects which have no significant effect on the structural strength of the structure.

Minor repair. Cirrus defines minor and major repairs the same as the FARs do. So, a minor repair would be a repair that is not a major repair.

Major repair. A major repair is a repair, that if done improperly might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or a repair that is not done according to accepted practices or cannot be done by elementary operations.

Cirrus allows major repairs in the field if the repair area does not fall into a no-repair zone, and it does not require non-standard repair procedures. In addition, field repair is allowed if the repair is specifically covered in the maintenance manual. All other major repairs need Cirrus Design engineering disposition.

Restricted. Any repairs that occur in no-repair zones as listed in the maintenance manual are restricted. The mechanic needs to contact Cirrus Design for disposition. Once we have gotten to this point, we know whether or not a repair is allowed in the area we are looking at. We can then begin the repair process. There are too many possible repair scenarios to cover in the limited space here, but we can cover some essential tips when performing the repair.

Repair environment

One thing you need to be aware of is the repair environment. For cosmetic repairs, the environment is not as critical. However, Cirrus has stringent environment requirements for minor and major repairs.

From our own safety perspective, we want to make sure the repair is carried out in an area that has adequate ventilation.

We also need to ensure that we are performing the repair in a controlled environment to ensure proper integrity of the repair and avoid any contamination issues. See the Repair Environment sidebar on this page for some guidelines on proper composite repair environment.

Ply orientation

When looking at a repair, we need to know the ply lay-up. The zone diagrams in chapter 51 of the maintenance manual provide that information. The charts contain information such as ply count and warp clocks. They show the zero-degree reference for each section of the airframe.

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