The valuation of such flight property properly apportioned to this state shall be determined to be the proportion of the total valuation thereof, based on the average of the total of the following three ratios for each type of aircraft:

(1) That ratio which the total tonnage of passengers, express and freight first received by the airline company in this state during the preceding calendar year plus the total tonnage of passenger, express, and freight finally discharged by it within this state during the preceding calendar year bears to the total of such tonnage first received by the airline company or finally discharged by it, within and without this state during the preceding calendar year;

(2) That ratio which the flight time of all aircraft of the airline company on flights serving this state during the preceding calendar year bears to the total of such time in flight within and without this state during the preceding calendar year;

(3) That ratio which the number of revenue ton miles of passengers, mail, express, and freight flown by the airline company on flights serving this state during the preceding calendar year bears to the total number of such miles flown by it within and without this state during the preceding calendar year.

Source: SL 1961, ch 449, § 7.