Roger Halstead wrote
The pilot can not be on the controls when the copilot is
operating as PIC.

This would have been a lot more correct if Roger had said
"when the copilot is flying the airplane". The PIC is the
PIC period.
Often, the PIC will perform the duties of a copilot and the
SIC will perform the duties of a pilot. More recent airline
terminology is "pilot flying" and "pilot not flying".

Bob Moore