41 C.F.R. § 301-10.101
Common carriers frequently update their levels of service and use various terminologies to distinguish those levels of service. For the purposes of this regulation, the classes of common carrier transportation are categorized as coach class, premium economy class, business class, and first class.
Note 1 to § 301-10.101: If an airline flight has only two classes of accommodations available, i.e., two distinctly different seating types (such as girth and pitch) and the front of the aircraft is termed "premium economy class" or higher by the airline and the tickets are fare coded as premium economy class or higher, then the front of the aircraft is deemed to be other than coach class. Alternatively, if an airline flight has only two seating sections available but equips both with one type of seating, (i.e., seating girth and pitch are the same in both sections of the aircraft), and the seats in the front of the aircraft are fare coded as full fare economy class, and only restricted economy fares are available in the back of the aircraft, then the entire aircraft is to be classified as coach class. In this second situation, qualifying for other than coach class travel is not required to purchase an unrestricted full fare economy seat in the front of the aircraft as the entire aircraft is considered "coach class."
41 C.F.R. §301-10.101