Except as provided in Sec. 91.873, after December 31, 1999, no person shall operate to or from any airport in the contiguous United States any airplane subject to Sec. 91.801(c) of this subpart, unless that airplane has been shown to comply with Stage 3 or Stage 4 noise levels. [Doc. No. FAA-2003-16526, 70 FR 38749, July 5, 2005]