cleeds, I finally found your definition of HTA, which you posted before my post about the difference if any between HTA and Zenith. Your definition of HTA:
"Your cartridge is in perfect alignment on the horizontal plane when a line drawn between the two contact facets form a straight line pointing at the center of the record."
For a cartridge where the stylus is perfectly cut and mounted on its cantilever and the cantilever is perfectly straight (problems mentioned by Dover) and one of the conventional alignment algorithms is perfectly observed, then the condition you describe occurs twice over the course of playing an LP, at each of the two null points, where Tracking Angle Error = 0. OK. That makes perfect sense. Now what is our definition of Zenith? If Zenith = HTA, then it must refer to the orientation of the stylus tip in the groove. That is not a conventional geometric definition of Zenith. Nor is it an aeronautical definition. (I consulted a close friend who is a pilot.) That's OK as long as we know what we mean.