As described in 14 CFR 91.225, ADS-B Out performance is required to operate in Class A, B, and C airspace. Above the ceiling and within the lateral boundaries of a Class B or Class C airspace area upward to 10,000 feet MSL. Note that ADS-B is not required in Class D airspace, or under a Class B or Class C airspace shelf, unless it lies within a Mode C veil, nor within TRSAs.