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The aircraft composite repair community will be facing new challenges over the coming years. Some of these are likely to prompt more training needs with the advent of commercial aircraft with composite primary structures – Boeing’s 787 and Airbus Industries’ A380, in particular. Training companies and composite-repair organizations are looking for better ways to keep their technicians more up to date on the latest developments in composite structures and repair techniques.
(Published on October-November 2005 – JEC Magazine #20)
Repair practices that may have been acceptable in the past could be inadequate on the newer, heavily-stressed structures coming into widespread use on newgeneration aircraft. As a result, detailed in-depth repair training for new technicians and training in the latest methods for current composite repair shops are essential.
Repair training expertise
Abaris Training Resources Inc. (Reno, Nevada, USA) has been conducting composite repair training for the military and commercial aircraft industry since 1983. President Michael Hoke says, “As a result of more composites being used in both secondary and primary structures, the aircraft industry is recognizing a need for more in-depth training. Much of the growth since 2001 has come from the military, although the commercial airline sector is strengthening.” The courses are also enrolling more general-aviation and helicopter repair technicians than in the past. An impact of 9/11 is that repair technicians from various parts of the world have found it difficult to get visas to the United States. In response, Abaris and Heatcon® (St. Ives, U.K.) formed a joint venture in late 2004 called Heatcon® Abaris Training International, which will provide repair training sites in other countries. The first location will be Lufthansa Resources’ facility in Cwmbran, Wales.
A variety of repair methods
While some repairs are performed on the aircraft, most suspect components are removed and sent to a repair facility.
Technicians inspect these components visually for surface defects such as pinholes, erosion, delaminations or small cracks. Coin-tap tests can uncover potential delaminations, while ultrasonic and other non-destructive inspection equipment can be used for more detailed examinations.
For smaller repairs, technicians remove the damaged area and perf o rm scarf sanding, a technique in which ply surfaces are removed in an even, t a p e red ratio of ply height to a given length. Scarfing ensures good bonding and distributed load transfer between the existing laminate and the patched a rea. Subsequent steps include surf a c e preparation, core fill, and application of the repair materials. Vacuum-bagging systems are used to provide compaction.
The repair patch might be cured in an autoclave or oven; or alternatively, heat from portable hot-bonding equipment can be delivered through heat blankets, lamps or hot air. Sometimes the most efficient and coste ffective means for correcting damage is to replace large sections or even entire face sheets. Another technique viable in thick solid laminates is to bolt in a doubler, which is a metal and/or p re c u red composite reinfo rcing panel that restores the load-bearing capacity of the component.