You cat bet it is:
http://www.vanityfair.com/news/2015/11/airplane-maintenance-...FTA:
>The airplanes that U.S. carriers send to Aeroman undergo what’s known in the industry as “heavy maintenance,” which often involves a complete teardown of the aircraft. Every plate and panel on the wings, tail, flaps, and rudder are unscrewed, and all the parts within—cables, brackets, bearings, and bolts—are removed for inspection. The landing gear is disassembled and checked for cracks, hydraulic leaks, and corrosion. The engines are removed and inspected for wear. Inside, the passenger seats, tray tables, overhead bins, carpeting, and side panels are removed until the cabin has been stripped down to bare metal. Then everything is put back exactly where it was, at least in theory.
>The work is labor-intensive and complicated, and the technical manuals are written in English, the language of international aviation. According to regulations, in order to receive F.A.A. certification as a mechanic, a worker needs to be able to “read, speak, write, and comprehend spoken English.” Most of the mechanics in El Salvador and some other developing countries who take apart the big jets and then put them back together are unable to meet this standard. At Aeroman’s El Salvador facility, only one mechanic out of eight is F.A.A.-certified. At a major overhaul base used by United Airlines in China, the ratio is one F.A.A.-certified mechanic for every 31 non-certified mechanics. In contrast, back when U.S. airlines performed heavy maintenance at their own, domestic facilities, F.A.A.-certified mechanics far outnumbered everyone else. At American Airlines’ mammoth heavy-maintenance facility in Tulsa, certified mechanics outnumber the uncertified four to one.