As used in this part:

(a) Air transportation has the meaning ascribed to it in 49 U.S.C. 40102(5).

(b) Carrier means any air carrier or foreign air carrier as defined in 49 U.S.C. 40102(2) or 49 U.S.C. 40102(21), respectively, that engages directly in scheduled passenger air transportation.

(c) Change-of-gauge service means a service that requires a change of aircraft en route but has only a single flight number.

(d) Ticket agent has the meaning ascribed to it in 49 U.S.C. 40102(a)(45).