Under sections 135.1 01 and 135.105, two pilots are required when carrying passengers under IFR unless an operative and approved autopilot system is installed, in which case one pilot is required. Although section 135.105 allows single-pilot operations with the use of an operative approved autopilot system, it does not require that all future flights be conducted in that manner. See Tarsa Interpretation (Mar. 26, 1992). In other words, the operator can elect either to operate under IFR with one pilot using the autopilot system or with two pilots, with the second pilot acting as SIC, without using the autopilot system. See id. Provided the certificate holder elects before the IFR operation to not use the autopilot system, then two pilots are required by the regulations under which the flight is conducted, and the pilot designated as SIC may log SIC flight time. If the autopilot system is used, then the pilot designated as SIC is not a required flight crewmember and may not log SIC time.