was the sole business of the corporation); 1982-1; 1981-6; 1981-26; 1982-12; 1989-22; 1993-27. Letter from David P. Byrne, Assistant Chief Counsel, FAA Regulations Division dated August 2, 1993 (the "Schwab opinion"), reproduced in Jackson and Edwards, Federal Aviation Regulations Explained, Parts 1, 61, 91, 141 and NT