14 CFR 247.1: Official mileage record of the Department of Transportation.

The direct airport-to-airport mileage record now maintained, and as hereafter amended or revised from time to time by the Office of Airline Information of the Bureau of Transportation Statistics of the Department of Transportation in the regular performance of its duties, is hereby adopted as the official mileage record of the Department and the mileages set forth therein shall be used in all instances where it shall be necessary to determine direct airport-to-airport mileages pursuant to the provisions of 49 U.S.C. Subtitle VII (Transportation)or any rule, regulation, or order of the Department pursuant thereto.