A pilot coming from an ACMI operator which uses augmented crews (IRO, for example), may have flown a trip as IRO, the duration of which was 13 hours. The flight departed LAX and landed ICN. During the course of that flight, the pilot filled the duties of IRO, including completing a plotting chart, making radio calls, etc, and spent several hours in the left seat, and several hours in the right seat.
At the conclusion of the flight, the 13 hours will count toward his commercial flying limitations. If he exceeds those limitations, he may be violated by the FAA. The FAA has repeatedly affirmed in numerous FAA Chief Legal Counsel Letters of Interpretation that flight time is block time and visa-versa. During the course of the flight, the IRO, a qualified SIC for XYZ Airways, was not pilot in command. He did operate the aircraft. He spent four hours in the right seat, and four hours in the left. He is a qualified SIC, assigned to duty by the certificate holder in a capacity in which is block time (eg, flight time) will count against his 30 day as 12 month limitations, etc.
During the four hours that the IRO relieved the captain, the captain took rest. The captain, being the pilot in command, will log PIC for the duration of the flight. At no point did he stop being the PIC of the flight. The first officer assigned the trip was relieved for four hours, during which he made coffee, moved to the IRO seat, visited the lav twice, picked his nose, tried to sleep (but couldn't), and drew a sea monster on the plotting chart. The First Officer was named first officer on the flight release and did not abdicate his position as SIC, but rotated seats as the IRO and captain moved about. His block time is his flight time and will count against his flight time limitations. All of it. The company will show it as SIC time in their records. He will log it as SIC.
The IRO, also assigned as an SIC for the trip (because he is not PIC), will log the duration of the flight as SIC. The FAA will hold the IRO accountable for those hours as they accrue in determining flight time limitations in the context of crew complement (eg, augmented vs. not, etc). The company will show the flight time (block time) for the trip for the IRO, the same as the F/O. It will count toward his limitations exactly the same.
When logging flight time, total time is either PIC or SIC, or for those with flight engineer background, FE time. One may also have been a student receiving instruction. For those who would log 13 hours of total time but only 8 hours of SIC, how do you account the other five hours of total time? What was it supposed to be, exactly, and what category do you suppose it fit?