Just like humans, airframes manufactured using composite materials are susceptible to different types of superficial skin wounds. Surface abrasions, that we call ‘hangar rash,’ are usually limited to minor damage caused to an aircraft whilst on the ground and often within the vicinity of a hangar, hence the term. It’s sustained usually 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. Sometimes very difficult to detect visually, serious ‘delamination’ is one of the most common types of composite damage and results from a major impact force, such as striking 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 approximately 27,000 ground accidents annually, which amounts to one incident per 1,000 departures. These events, all of which are preventable, are responsible for some $10 billion in damages, most of which has to be absorbed by the owner/operator, as rectification costs would generally 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, so the statistics from the FSF are unlikely to reduce significantly. Where vehicles and equipment need to be in close proximity, 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 period 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 eight to 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. Mobile inflatable cleanrooms, which our business pioneered, provide a simple, fast and cost-effective solution for enabling outdoor composite repair on the line, when a hangar is not available. These ensure the optimum environment for repairing composite parts which have been removed from the aircraft. These lightweight and 100% weatherproof units deliver all of the benefits of a conventional cleanroom but can be erected in just 15 minutes to free up space in a hangar or shipped directly to a repair site.
The structure can be set up right next to an aircraft, enabling the on-site repair of components that have been removed from the aircraft without having to take them to another facility. To be able to take something from a box, inflate, heat and air-condition it in all weather conditions and have it operational within minutes, is of massive benefit to airlines and their skilled engineers working with composites.
On the subject of heating, advances in technology have also facilitated the introduction of an inflatable oven that can be heated up to 200°C. In support of composite repairs, this can be mounted on any part of the fuselage or used as a free-standing unit, enabling fast treatment of composite material, which is extremely time and cost-efficient.
Similarly, there has been a significant rise in the requirement for airframe modifications which facilitate better inflight communications capability. The availability of on-board WiFi for passengers is being used as a key customer benefit in airline marketing but retrofitting airline fleets for connectivity firstly requires approval in the form of Supplemental Type Certificates (STCs). With many MROs and airlines focusing on the provision of WiFi on their aircraft and antennas continually being upgraded, it’s a process which is seeing rapid acceleration within the industry.
Carrying out such complex modifications presents practical engineering challenges. WiFi antennas need to be fitted to the crown of the aircraft, either inside or outside the hangar. When inserting these into the airframe, engineers need to mitigate against dust contamination, whilst working within strict humidity and temperature tolerances. Again, the versatility of inflatable protection modules not only provides additional safety and security for engineers working on top of the aircraft, but it also ensures the ideal conditions for this modification to be executed successfully.
In light of the current worldwide health crisis affecting global aviation, cost and time-efficiency for aircraft maintenance, repair and modifications will be absolutely critical elements in helping the sector to recover over the months and years ahead. Those of us who are innovators in design and manufacture will play a crucial role in supporting the industry during the most challenging time we have ever faced since the Wright Brothers first took to the skies.
Founded by Ian Nagle to serve the Irish haulage industry back in the mid-1980s, Cork-based JB Roche diversified into manufacturing framed canvas products for the marine industry. Its investment in design and patterning software and automated cutting equipment laid the foundations for JB Roche’s move into the aviation sector, when it developed an inflatable hangar solution for Aer Lingus. Since inventing and patenting the world’s first precision fit, all-fabric inflatable aircraft hangar in 1999, JB Roche continues to be at the forefront of advanced inflatable shelters for the global aviation sector.
