otes that although the NLRA and the RLA share several common features, the NLRA was not perfectly modeled after the RLA. See Bhd. of R.R. Trainmen v. Chi. River & Ind. R.R. Co., 353 U.S. 30, 31 n.2 (1957) (“The relationship of labor and management in the railroad industry has developed on a pattern different from other indus