MIL-HDBK-17-3F Volume 3,Chapter 8 Supportability tential galvanic corrosion that may be caused by contact with the carbon fibers.This may require removal of fasteners at mating surfaces,so blind fasteners should not be used in these applications.The use of blind titanium fasteners should be kept to a minimum because,when installed,they are literally impossi- ble to inspect to verify correct installation.They are also very difficult to remove when repairing or replac- ing a component. 8.2.2.2 Accessibility for inspection Composite structural components should not be designed such that they must be removed in order for inspections to be made.Some disassembly may be unavoidable,but should be kept to a minimum. This will not only reduce the maintenance burden on the operators,but also reduce airplane out-of- service time. All composite components should be designed to ensure visual accessibility of the external surfaces without detaching any parts,including access panels,from the airplane.In some instances,fairing panels may have to be removed,such as the horizontal stabilizer-to-fuselage fairing for access to the stabilizer skin joints-to-side-of-body rib,or spar-to-center-section attachments. An internal inspection implies that there is visual accessibility that is achieved by removal of detach- able parts,such as access plates or panels.For internal inspection of torque boxes with ribs,spars and stringers,there must be complete visual accessibility through access holes in spars and ribs.These ac- cess holes must be designed such that maintenance technicians can,through the use of flashlights and mirrors,visually inspect all of the internal structure.There must also be accessibility to critical joints or attachment fittings where pins can be removed so that they and the holes can be inspected. 8.2.3 Material selection 8.2.3.1 Introduction Chapter 2 in Volume 3 offers an in-depth review of advanced composite materials.Each one of the composite materials described in Chapter 2 can offer benefits over metallic materials to the designer in terms of performance and costs.However,these benefits will be erased if,when designing a component, the design is focused only on the mechanical and thermal performance of the component and does not take into consideration where the part will be used and how it will be repaired if it is damaged.The goal of the designer must be to design a part that will be both damage tolerant and damage resistant as well as easy to maintain and repair.This section is offered as a guideline for the designer when selecting a mate- rial system. 8.2.3.2 Resins and fibers When selecting a resin,it is important to look at where the resin system will be used,how the resin system has to be processed,what is its shelf life and storage requirements,and is it compatible with sur- rounding materials.Table 8.2.3.2 describes the common resin types,their process conditions and their advantages and disadvantages in terms of repairability.An in-depth review of these materials can be found in Section 2.2. Refer to Section 2.3 for available fibers for composite structures. In terms of supportability,the minimum number of resin systems and material specifications should be chosen.This will reduce the logistic problems of storage,shelf life limitations and inventory control. 8-7MIL-HDBK-17-3F Volume 3, Chapter 8 Supportability 8-7 tential galvanic corrosion that may be caused by contact with the carbon fibers. This may require removal of fasteners at mating surfaces, so blind fasteners should not be used in these applications. The use of blind titanium fasteners should be kept to a minimum because, when installed, they are literally impossi￾ble to inspect to verify correct installation. They are also very difficult to remove when repairing or replac￾ing a component. 8.2.2.2 Accessibility for inspection Composite structural components should not be designed such that they must be removed in order for inspections to be made. Some disassembly may be unavoidable, but should be kept to a minimum. This will not only reduce the maintenance burden on the operators, but also reduce airplane out-of￾service time. All composite components should be designed to ensure visual accessibility of the external surfaces without detaching any parts, including access panels, from the airplane. In some instances, fairing panels may have to be removed, such as the horizontal stabilizer-to-fuselage fairing for access to the stabilizer skin joints-to-side-of-body rib, or spar-to-center-section attachments. An internal inspection implies that there is visual accessibility that is achieved by removal of detach￾able parts, such as access plates or panels. For internal inspection of torque boxes with ribs, spars and stringers, there must be complete visual accessibility through access holes in spars and ribs. These ac￾cess holes must be designed such that maintenance technicians can, through the use of flashlights and mirrors, visually inspect all of the internal structure. There must also be accessibility to critical joints or attachment fittings where pins can be removed so that they and the holes can be inspected. 8.2.3 Material selection 8.2.3.1 Introduction Chapter 2 in Volume 3 offers an in-depth review of advanced composite materials. Each one of the composite materials described in Chapter 2 can offer benefits over metallic materials to the designer in terms of performance and costs. However, these benefits will be erased if, when designing a component, the design is focused only on the mechanical and thermal performance of the component and does not take into consideration where the part will be used and how it will be repaired if it is damaged. The goal of the designer must be to design a part that will be both damage tolerant and damage resistant as well as easy to maintain and repair. This section is offered as a guideline for the designer when selecting a mate￾rial system. 8.2.3.2 Resins and fibers When selecting a resin, it is important to look at where the resin system will be used, how the resin system has to be processed, what is its shelf life and storage requirements, and is it compatible with sur￾rounding materials. Table 8.2.3.2 describes the common resin types, their process conditions and their advantages and disadvantages in terms of repairability. An in-depth review of these materials can be found in Section 2.2. Refer to Section 2.3 for available fibers for composite structures. In terms of supportability, the minimum number of resin systems and material specifications should be chosen. This will reduce the logistic problems of storage, shelf life limitations and inventory control