14 C.F.R. § 61.325
If you hold a sport pilot certificate and seek privileges to operate an aircraft meeting the performance limits and design requirements of § 61.316 in Class B, C, or D airspace, at an airport located in Class B, C, or D airspace, or to, from, through, or at an airport having an operational control tower, you must receive and log ground and flight training. The authorized instructor who provides this training must provide a logbook endorsement that certifies you are proficient in the following aeronautical knowledge areas and areas of operation:
[Docket FAA-2001-11133, 69 FR 44869, July 27, 2004, as amended by Docket FAA-2023-1377, Amdt. 61-159, 90 FR 35218, July 24, 2025]