14 C.F.R. § 91.1031 – Pilot in command or second in command: Designation required.

(a) Each program manager must designate a—
1. (1) Pilot in command for each program flight; and
2. (2) Second in command for each program flight requiring two pilots.
(b) The pilot in command, as designated by the program manager, must remain the pilot in command at all times during that flight.