(2) In the case of any other transportation by air, that portion of such transportation that is directly or indirectly from one port or station in the United States to another port or station in the United States, but only if such transportation is not part of uninterrupted international air transportation within the meaning of section 4262(c)(3) of the Code and § 49.4262-3(c) . Transportation from one port or station in the United States occurs whenever a carrier, after leaving any port or station in the United States, makes a regularly scheduled stop at another port or station in the United States irrespective of whether stopovers are permitted or whether passengers disembark. The provisions of this paragraph are applicable whether the transportation is by rail, motor vehicle, water, or air, or any combination thereof, except that with respect to transportation which begins after November 15, 1962, the tax, if applicable, applies only to the amount paid for that portion of the transportation which is by air.