WHEN the Harrier GR 5 begins operations, the Royal Air Force will have an aircraft of which one quarter of the structure weight is composites and one half of the structure area. Major primary structure components are fabricated from carbon fibre composites (CFC) whose characteristics are notably different from light alloys. These differences have to be taken into account when appreciating the problems of supporting such an aircraft and providing the best methods of effecting repairs to damaged structure.