The minimum flight crew must be established so that it is sufficient for safe operation, considering--
(a) The workload on individual crewmembers;
(b) The accessibility and ease of operation of necessary controls by the appropriate crewmember; and
(c) The kind of operation authorized under Sec. 25.1525. The criteria used in making the determinations required by this section are set forth in appendix D. [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-3, 30 FR 6067, Apr. 29, 1965]