Just like us humans, airframes manufactured using composite materials are susceptible to different types of superficial skin wounds. Surface abrasions, colloquially known as ‘hangar rash’ are usually limited to minor damage caused to an aircraft whilst on the ground and typically within the vicinity of a hangar, hence the term.
Such damage is often sustained as a result of vehicles or ground equipment coming into contact with the fuselage, engine nacelles or wing surfaces, resulting in cosmetic scratches or punctures to the laminate. Often difficult to detect, serious ‘delamination’ is one of the most common types of composite damage and results from a major impact force, such as hitting a hangar door or even a mid-air bird strike. This causes a separation or fracture of the laminated reinforcement layers or plies.
According to data submitted to the Flight Safety Foundation (FSF) by international airlines, there are around 27,000 ground accidents annually, which amounts to one incident and also 9 injuries to personnel, per every 1,000 departures. These events which it should be noted, are all preventable, are responsible for some $10 billion in damages, most of which has to be absorbed by the owner/operator, as the rectification costs fall below the threshold for insurance claims.
Whilst MROs have performed composite repairs for years, these were usually only carried out on the airframe if the part was too large and/or expensive to remove. Materials and technology have moved on significantly, so repairs on the line are increasingly seen as the norm, thereby reducing static aircraft (AOG).
Composites in aircraft manufacture came of age with the introduction of Boeing’s 787 and the Airbus A350 XWB. Its use has extended far beyond flaps, ailerons and other control surfaces, engine nacelles and empennage, to encompass the entire forward wing structure and fuselage.
As well as achieving a reduction in weight to improve fuel efficiency, another major benefit of composite airframes is a drastic reduction in corrosion and fatigue-related maintenance. In fact, Airbus claims a 60% reduction in these tasks for the A350 XWB, cutting both the time required to perform maintenance checks and the total number of checks required over the aircraft’s service life. Whilst the 787 and A350 XWB are still very young, it is widely acknowledged that the real test will come in the next 5-10 years.
Having said that, irrespective of an aircraft’s construction, airports are becoming increasingly congested as global air traffic surges, so the statistics from the FSF are unlikely to take a dramatic dive. Accidents will still happen, despite initiatives designed to prevent collisions on the ramp.
Working on aircraft with more expansive and increasingly complex composite structures does create challenges for MRO providers. One is the need to perform an increasing number of repairs on the aircraft versus in a hangar. Another is to reduce the duration of repair without any compromise in quality. A third is to increase the size limit and application for approved bonded repairs to more complex and primary structures.
By its very nature, repairing a composite structure usually means greater downtime because of the curing time demanded by specific resins and adhesives. The adhesive and prepreg (pre-impregnated) layers used in bonded composite repairs, where a repair patch is adhesively bonded to replace the damaged material, can take 8-12 hours to cure. Furthermore, the processes involved in non-destructive inspection of the affected area, removing damaged material and preparing for bonding are typically lengthy. Therefore, technologies designed to abbreviate repairs and reduce turnaround time (TAT) are increasingly sought after by airlines.
Of critical importance during the adhesive curing process is the need for absolute cleanliness, to ensure the integrity of the bond is not affected by any foreign matter. Unique, inflatable cleanrooms designed and manufactured by J B Roche provide a simple, fast and cost-effective solution for enabling outdoor composite repair on the line, when a hangar is not available.
The Cork-based company’s fully patented CompShop ensures the optimum environment for repairing composite parts which have been removed from the aircraft. This lightweight and 100% weatherproof unit offers all of the benefits of a conventional cleanroom but it can be relocated in just a few minutes to free up space in a hangar or shipped directly to a repair site, where it can be erected in just 15 minutes by a small maintenance team without the need for prior training.