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Composite Airframe Ground Damage Risk
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Ramp accidents cost airlines significant amounts of money but these accidents only become a flight safety risk if they represent an airworthiness risk and are either undetected or unreported. The increasing use of composite materials in aircraft manufacturing may lead to increased risk because often, after being hit, a composite surface returns to its original shape and the damage underneath is not visible to the naked eye. A simple ‘tap’ test might not detect a delamination at an early stage or in specific areas.
The operational safety emphases are:
- Avoidance - reduce the risk of damage occurring.
- Correct Response to events which may have caused damage
- Education - explaining to personnel why it is important to report accidents even if there is no visible evidence of damage.
Composite Airframe 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
Any impact with a composite aiframe, no matter how slight, should be immediately reported to the Pilot in Command (PIC) of the aircraft if present or the aircraft operator's line engineering agency at the airport. The location and nature of the impact must be recorded accurately. As many 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.
Operators and ramp handling agencies need to have robust education and response processes in place and properly documented. All personnel who work in close proximity to aircraft must:
- Understand that composite structures may not have any visible signs of structural damage after even a minor impact and
- Fully appreciate the critical importance of immediately reporting any impact to an appropriate person who is in a position to ensure that the aircraft does not depart for a flight without an assessment of the extent of any risk to flight safety by a competent and appropriately qualified specialist.
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 first 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.
- Non Destructive Testing of Composite Materials in Aviation
- Minor Repair Responses to Composite Airframe Damage
- Status of FAA’s Actions to Oversee the Safety of Composite Airplanes: US Government Accountability Office (GAO), September 2011.
- Visual Inspection Reliability For Composite Aircraft Structures; Lawrence Cook, Cranfield University, October 2009.
- CODAMEIN - Composite Damage Metrics and Inspection (high energy blunt impact threat), EASA, March 2012.
- CAP 562 - Leaflet 51-170 Inspection of Composite Structures
- Making Composite Repairs to the 787, Boeing AERO magazine, issue Q4 2014