Thanks for the reply.
Your first question
The copilot can log PIC time, as long he is a required crew member.
But under what circumstances?
The "sole manipulator of controls" paragraphs does not seem to be referenced to multicrew environments by virtue of the fact that later paragraphs explicitly do reference multicrew environments.
Furthermore, the FAA's definition of PIC makes no reference to being the sole manipulator of controls as being part of the definition of PIC.
If this is the case, it would seem that the rules confuse "pilot flying / pilot not flying" with "PIC / SIC" which are very different concepts in multicrew.
Your second question.
Yes, the supervising pilot must be a CFI. It's all about training here.
A safety pilot on a simulated IFR flight, can not log PIC time, because he is not the sole manipulator of the controls. He is a required crew member, but not a CFI doing training. He/she is not supervising.
So if a co-pilot ever wishes to log PIC time, the accompanying captain must be an FAA CFI?
An ATP is needed for ... airline work.
Are there any regulations which point to this? Where does the definition of an airline come from? A small puddle-hopper? A widebody jet? Does scheduled public transport by rotorcraft count?
Thanks again for the reply.