This article provides an overview of the advantages of composite airframes (used in the Boeing 787 and Airbus A350 aircraft) and elaborates on their repairability and the methods to respond to minor damages.
Composite Airframes Benefits
Composite airframes have a number of advantages over the traditional metal structures:
composite parts of the same size are lighter, leading to fuel savings
composite parts are not subject to fatigue
composite parts are not affected by corrosion
composite materials have better strength-to-weight ratios that allow various improvements, e.g. larger windows, lower altitude cabin pressure, etc.
composite materials are generally more resistant to impact damage compared to aluminum
A major issue with composite airframes is that minor surface damage does not accurately reflect the extent of damage beneath the surface. What may appear to be insignificant damage on the surface could mask damage to the layers of material beneath the surface, compromising its strength. This could allow an aircraft with potentially significant damage to be operated. Therefore, ramp workers need to be aware of the importance of reporting even minor (or what appears to be minor) contact with the aircraft. As most ramp employees may not have sufficient knowledge about composite aircraft maintenance, it is critical that supervisors know that even the most minor damage needs to be reported.
A major benefit of composite aircraft is they offer lower maintenance costs. Boeing claims that the 787’s composite structure has airframe maintenance costs that are 30 percent lower than any comparable airplane. This is mainly due to the resistance to corrosion and fatigue. In addition, aircraft manufacturers have developed procedures and materials that allow quick and reliable repairs that shorten aircraft down time considerably without compromising safety. The four main areas adressed are:
Damage assessment - since the damage is often not as visible as with aluminum parts (where the material is dented or torn) a simple visual ispection is usually not sufficient for this task. Therefore, aircraft manufacturers develop methods and tools to quickly and accurately determine the extent of damage.
Ramp-rash events - these are incidents on the ground where the aircraft gets hit by a vehicle, airbridge, etc. When damage is determined to be minor, quick repairs to the composite surface can be accomplished in about an hour using a repari kit. For instance, the Boeing quick composite repair kit kit includes sanding disks, gloves, lint-free wipes, vacuum bag flm, structural patches, anti-caul foil patches, heat pack, and adhesives. The areas of the airplane where Quick Composite Repairs can be used and application instructions are provided in the respective manuals.
Lightning strikes - While lightning strike damage can occur to composite structures, the damage is often minimal and repairable with a time-limited repair. The damage must frst be inspected for size and depth. After consulting the manual, the proper course of action is chosen. Sometimes the lightning damage can be sealed with resin or aluminum foil tape as a temporary repair and service can resume immediately until the aircraft can be put into maintenance at a more convenient time. If the damage is larger than allowable limits, it can usually be repaired using wet layup methods.
Large area damage - this type of damage is generally considered to be an area of approximately 1 meter by 1 meter or larger and is repaired using a pre-cured panel bolted in place with splicing straps and doublers. This method has been successfully performed in-service.