For the purposes of this subsection, industry means a trade, business, industry, or other activity, or branch, or group thereof, in which individuals are gainfully employed (section 3(h) of the Fair Labor Standards Act of 1938, as amended (Public Law 93-259)); (i) Any hours worked by an employee of a carrier by air subject to the provisions of subchapter II of the Railway Labor Act (45 U.S.C. Se