Having a blond moment here. Never heard/seen this before. GuS wears a HAT would equate to HAT/GS, GS being the descent angle?
Hehe.....blondie.
Yes, GuS wears a HAT being the mnemonic to help remember the formula: divide desired GlideSlope angle into the Height Above Touchdown. Or otherwise, GuS wears a HAT. The distance you come up with from there is calculated back from the runway threshold, or begining of the runway. Some people say calculate it back from the MAP, but the MAP and the runway beginning
may not be coincidental. For instance, look at the TACAN 29R at KTUS. HAT is 477' with a 3.55 degree GS. Doing GuS wears a HAT and dividing that by 100, you get 1.34...or nominally 1.3 miles. Working back 1.3 miles from the runway, you get a VDP DME of 0.7 from the TUS VORTAC, or about 0.4nm short of the MAP at HOSVO. In this instance, if you calculated the VDP back from the MAP (looking at the distance markers back from the runway in the profile view), you'd get a VDP way back at 1.6 DME from the VORTAC or back near GAVET, which is about 2.5nm from the runway threshold. If you were to commence your descent at that point, you'd be shallow with about a 2 degree glidepath and nowhere near the 3.55 degrees you did the calculation for;
because you ran the calculation back from the MAP instead of the runway threshold (you're calculating a descent angle to get to the runway, but if the MAP and runway threshold
aren't coincident, then your VDP is inaccurate. Is it dangerous? It could be if there are obstructions that your shallow and inaccurate VDP now won't keep you clear of. Thats why you calculate back from the runway threshold and not the MAP, even though they're oftentimes coincidental, but not always. Again, to be perfectly accurate, you want to measure your desired glidepath to the runway,
not to somewhere short of the runway that computing from a non-coincident MAP will lead you to.
http://204.108.4.16/d-tpp/1011/00430VDT29R.PDF
Now, looking at a more "normal" IAP where the MAP and approach end of the runway are concident, you'll see where I'm correct. Take the TACAN 11L into KTUS. You have a HAT of 361' and a 3.05 GS angle. Applying GuS wears a HAT and again dividing that by 100, you get 1.18....or 1.2nm. Calculating back from the runway threshold, you get 3.6 DME (2.4 DME at the rwy threshold + 1.2 DME back= 3.6 DMEVDP), although the plate is showing 3.4 DME (or 1.0 NM back from the runway threshold) for that calcuation, which tells me that the VDP depicted would give you a 3.5 degree glidepath to the runway threshold.
http://204.108.4.16/d-tpp/1011/00430VT11L.PDF