The FAA puts forward a lot of aerodynamic literature that is either oversimplified or flat-out incorrect. Just reference the ongoing battle to teach Newtonian principles in initial aerodynamic theory courses in addition to the FAA-sanctioned over-application of Bernoulli's Principle. Long story short, starting in the 1950's, a lot of these complicated principles were dumbed down to "our level" on the basis that we're pilots, not mathematicians, and we don't need to (or simply can't) understand the full story. When you go full Math Nerd and really get into the physics in play, you find yourself needing to unlearn a lot of The Sacred Truths as taught in ground school.
I'm in serious danger of throwing this discussion way off topic, so to get back to what the OP was asking: The existence of P-Factor is predicated on the propeller operating in an AoA other than zero. A propeller producing thrust at a zero degree AoA will not create P-Factor. A propeller producing thrust at very-near-to-zero degree AoA will produce P-Factor, but the asymmetry is negligible compared to the other factors cited. The term "Critical Engine" doesn't really apply on the ground the same way it does in the climbout.
Last edited by thepotato232; 4th February 2010 at 01:25.