Well the safety pilot logging PIC is an approved FAA method to have two pilots log time on a single-pilot airplane, but I know some airlines that do not accept such time toward their hiring minimums, and in my mind the spirit of the principle has to do with helping a left seat pilot practice doing approaches in VFR conditions for IFR currency or IFR flight training, neither of which really is the point of a twin-engine airplane doing long cross countries for time building purposes. I can only guess why some airlines don't count it, but I'll venture a guess they think it represents a lot of time watching the world go by as the right seat pilot does little as far as flying the airplane is concerned. Another reason may be that as you mention, the left side pilot is supposed to be wearing a view limiting device, but it is a skeptical thing to believe he or she is going to wear a hood for 7 hours at a time as specified.
As far as the back-seater goes, that is also legal as far as the FAA is concerned and he or she may log PIC as well, but his or her participation is obviously fairly limited. And one might argue from a learning perspective that they should not be there anyway, the pilots up front should thinking for themselves. If there is an emergency, then what can they do from the back seat except repeat the contents of the pilots operating handbook? As Ryan says, it has more to do with insurance than with learning. Once again, I do not take sides in it, just trying to point out some of the typical controversies.
Last edited by Cubdriver; 02-21-2010 at 10:21 AM.