14 CFR § 121.392

Any person identified by the certificate holder as a flight attendant on an aircraft in operations under this part must be trained and qualified in accordance with subparts N and O of this part. This includes:

Flight attendants provided by the certificate holder in excess of the number required by § 121.391(a); and

Flight attendants provided by the certificate holder when flight attendants are not required by § 121.391(a).

A qualifying flight attendant who is receiving operating experience on an aircraft in operations under subpart O of this part must be identified to passengers as a qualifying flight attendant.