14 CFR §91.861

1. (a)U.S. Operators. The base level of a U.S. operator is equal to the number of owned or leased Stage 2 airplanes subject to § 91.801(c) of this subpart that were listed on that operator's operations specifications for operations to or from airports in the contiguous United States on any one day selected by the operator during the period January 1, 1990, through July 1, 1991, plus or minus adjustments made pursuant to paragraphs (a) (1) and (2).
   1. (1)The base level of a U.S. operator shall be increased by a number equal to the total of the following—
      1. (i)The number of Stage 2 airplanes returned to service in the United States pursuant to § 91.855(f);
      2. (ii)The number of Stage 2 airplanes purchased pursuant to § 91.855(g); and
      3. (iii)Any U.S. operator base level acquired with a Stage 2 airplane transferred from another person under § 91.863.
   2. (2)The base level of a U.S. operator shall be decreased by the amount of U.S. operator base level transferred with the corresponding number of Stage 2 airplanes to another person under § 91.863.
2. (b)Foreign air carriers. The base level of a foreign air carrier is equal to the number of owned or leased Stage 2 airplanes that were listed on that carrier's U.S. operations specifications on any one day during the period January 1, 1990, through July 1, 1991, plus or minus any adjustments to the base levels made pursuant to paragraphs (b) (1) and (2).
   1. (1)The base level of a foreign air carrier shall be increased by the amount of foreign air carrier base level acquired with a Stage 2 airplane from another person under § 91.863.
   2. (2)The base level of a foreign air carrier shall be decreased by the amount of foreign air carrier base level transferred with a Stage 2 airplane to another person under § 91.863.
3. (c)New entrants do not have a base level.