Except as provided in paragraph (a) of this section, each operator that operates an airplane under part 91, 121, 125, 129, or 135 of this chapter, regardless of the national registry of the airplane, shall comply with paragraph (b) or (d) of this section at each interim compliance date with regard to its subsonic airplane fleet covered by § 91.801(c) of this subpart.

This section does not apply to new entrants covered by § 91.867 or to foreign operators not engaged in foreign air commerce.

Each operator that chooses to comply with this paragraph pursuant to any interim compliance requirement shall reduce the number of Stage 2 airplanes it operates that are eligible for operation in the contiguous United States to a maximum of:

After December 31, 1994, 75 percent of the base level held by the operator;

After December 31, 1996, 50 percent of the base level held by the operator;

After December 31, 1998, 25 percent of the base level held by the operator.

Except as provided under § 91.871, the number of Stage 2 airplanes that must be reduced at each compliance date contained in paragraph (b) of this section shall be determined by reference to the amount of base level held by the operator on that compliance date, as calculated under § 91.861.

Each operator that chooses to comply with this paragraph pursuant to any interim compliance requirement shall operate a fleet that consists of:

After December 31, 1994, not less than 55 percent Stage 3 airplanes;

After December 31, 1996, not less than 65 percent Stage 3 airplanes;

After December 31, 1998, not less than 75 percent Stage 3 airplanes.

Calculations resulting in fractions may be rounded to permit the continued operation of the next whole number of Stage 2 airplanes.