Whoevers name is listed on the flight plan as PIC will be the PIC in an incident / accident;
This is not true. Under Parts 121 and 135 the pilot designated PIC by the certificate holder will remain the PIC for the entire flight. However, there is nothing about being listed as PIC on a filed flight plan that makes one the PIC, nor assigns any particular responsibility.
Under Part 91 operations only, pilots may interchange the responsibility of being PIC by mutual agreement. This is not particular to any seat, nor a "seat locked" responsibility.
Further, under parts 121 or 135 (which I take the flight in question not to be), the assigned PIC need not be in the left seat. In other words, the responsibility of PIC doesn't stay with the seat, but with the assigned pilot. If the company designated PIC for a flight under 121 or 135 moves to the right seat or climbs out of the seat, he or she is still PIC. The company may designate a different pilot to be PIC during that time, such as captain A will be PIC when flying leg AA, and captain B will be PIC when flying leg BB.
If a pilot under 121 or 135 is PIC and steps off the flight deck (rest, psyiological needs, etc), he or she is still PIC when not present, and still holds the responsibities of being PIC.
Someone asked about the PIC being off the flight deck while the PF misses an altitude or clearance during a descent...who is responsible? Both the PIC, as PIC, and the PF who missed the altitude or clearance. Both may be held accountable.
Conversely, consider the scenario where the captain, acting as PIC is also pilot flying. He is being barraged by a F/O who won't shut up, and doesn't hear an altitude ammendment while he is descending on a descent clearance. Consequently he busts the altitude. Upon investigation, it's entirely possible that the F/O will be violated and the captain will not. Circumstances dictate, despite PIC responsibilities. As required crewmembers, each crewmember is culpable for his or her duties, interference in others duties, and each person's actions.
Of course, that's why we're crew, and not just "a-bunch-of-guys-or-gals-in-the-cockpit (ABOG/GIC).
