In general. Under section 4262(b) taxable transportation does not include that portion of any transportation which meets all four of the following requirements:

Such portion is outside the United States;

Neither such portion nor any segment thereof is directly or indirectly:

Between (a) a point where the route of the transportation leaves or enters the continental United States, or (b) a port or station in the 225-mile zone, and

A port or station in the 225-mile zone;

Such portion:

Begins at either (a) the point where the route of the transportation leaves the United States, or (b) a port or station in the 225-mile zone, and

Ends at either (a) the point where the route of the transportation enters the United States, or (b) a port or station in the 225-mile zone; and

A direct line from the point (or the port or station) specified in subparagraph (3) (i) of this paragraph, to the point (or the port or station) specified in subparagraph (3) (ii) of this paragraph, passes through or over a point which is not within 225 miles of the United States. For purposes of this section, the route of the transportation shall be deemed to leave or enter the United States when it passes over (i) the international boundary line between any part of the United States and a contiguous foreign country, or (ii) a point three nautical miles (3.45 statute miles) from low tide on the coast line.

Transportation to or from Alaska or Hawaii. (1) Under the provisions of section 4262(b) transportation between the continental United States or the 225-mile zone and Alaska or Hawaii will be partially exempt from the tax. The portion of such transportation which (i) is outside the United States, (ii) is not transportation between ports or stations within the continental United States or the 225-mile zone, and (iii) is not transportation between ports or stations within Alaska or Hawaii, meets all the requirements set forth in section 4262(b) and is excluded from taxable transportation.

The provisions of subparagraph (1) of this paragraph may be illustrated by the following examples:

A buys a ticket for transportation by air from Seattle to Fairbanks, Alaska, via Ketchikan and Juneau, Alaska, and Whitehorse, Yukon Territory, Canada. The portion of the transportation between the point where the route of the transportation leaves the continental United States and the point where it first enters Alaska (the three-mile limit or the international boundary) is not subject to tax.

B purchased combination rail-water transportation beginning before November 16, 1962, from Chicago to Juneau, Alaska, by way of Vancouver, Canada. The portion of the transportation from Vancouver to the point where the route of the transportation enters the three-mile limit off the coast of Alaska is not subject to tax.

C purchases a ticket in the United States for transportation by air from Vancouver, Canada, to Honolulu, Hawaii. No part of the route followed by the carrier passes through or over any part of the continental United States. The only part of the payment made by C for this transportation which is subject to the tax is that applicable to the portion of the transportation between the three-mile limit off the coast of Hawaii and the airport in Honolulu.

Method of computing tax on travel not excluded. (1) Where a payment is made for transportation which includes transportation excluded under the provisions of section 4262(b):

The tax may be computed on that proportion of the total amount paid which the mileage of the taxable portion of the transportation bears to the mileage of the entire trip, or

If the taxable portion of the transportation includes transportation from one port or station to another port or station for which an applicable local fare of a like class is available, the tax may be computed on the amount of such local fare, plus an amount equivalent to that proportion of the remainder of the total amount paid which the mileage of the remainder of the taxable portion of the transportation bears to the remainder of the mileage of the entire trip. If the taxable transportation includes a leg from a station to a coastal gateway point of embarkation for which a uniform fare is charged regardless of the gateway point actually used, the tax on such a leg may be computed on the basis of such uniform fare. In the absence of a fare described in this subparagraph, the tax must be determined in accordance with subdivision (i) of this subparagraph. If the taxable portion of the transportation includes a leg between coastal gateway points of embarkation for which no additional fare is charged no tax shall be applicable to such leg of the transportation.

The basis for determining the proportions described in subdivisions (i) and (ii) of subparagraph (1) of this paragraph shall be the average mileage of the established route traveled by the carrier between given points under normal circumstances.

Illustration. The application of paragraph (c) of this section may be illustrated by the following example:

On October 10, 1959, A purchases in San Francisco a ticket for transportation by air to Honolulu, Hawaii. The portion of the transportation which is outside the continental United States and is outside Hawaii is excluded from taxable transportation. The tax applies to that part of the payment made by A which is applicable to the portion of the transportation between the airport in San Francisco and the three-mile limit off the coast of California (a distance of 15 miles) and between the three-mile limit off the coast of Hawaii and the airport in Honolulu (a distance of 5 miles). The part of the payment made by A which is applicable to the taxable portion of his transportation and the tax due thereon are computed in accordance with paragraph (c)(1) as follows: