from https://www.federalregister.gov/arti...rt-air-traffic


Under paragraph (b)(1) of that section, in order to operate an aircraft below 18,000 feet MSL and in identified airspace described subsequently in § 91.225, an aircraft must be equipped with equipment that "meets the requirements of TSO-C166b; or TSO-C154c . . .". In reviewing these paragraphs, the FAA notes that the regulatory text implies that the equipment must meet all the requirements of the referenced TSOs. As the ADS-B Out rule is a performance-based rule, it was not the FAA's intent to arguably limit operators to only install equipment marked with a TSO in accordance with 14 CFR part 21, subpart O. The FAA's intent was to permit equipment that meets the performance requirements set forth in the referenced TSOs.


In the NPRM, the FAA proposed in § 91.225(a)(1) and (c)(1) that the equipment installed "Meets the performance requirements in TSO-C-166a" (72 FR 56947, 56971). The inadvertent removal of the word "performance" in the paragraphs implementing these provisions in the final rule was in error and resulted in confusion as to whether the regulation permits other than equipment marked with a TSO, provided that equipment met the specified performance requirements.


So it looks like the equipment must meet the TSO performance requirements, but it doesn't necessarily have to be TSO'd

This is great news!