61.51(e)(3) An authorized instructor may log as pilot-in-command time
all flight time while acting as an authorized instructor.

Seems to me this says that it has to be flight time first, he has to be
acting as an authorized instructor =during= that flight time, and =then=
he can log it as PIC time.

If it's not flight time to begin with, this rule does not let him log it
as PIC time. It does not prohibit it either - that prohibition comes
from elsewhere (except as provided in...may log as PIC time only that
time in which...)

Jose
--
Math is a game. The object of the game is to figure out the rules.
for Email, make the obvious change in the address.