Originally Posted by
A Squared
That isn't the source of the discrepancy here. The difference between 2.81 degree glidepath and a 3.06 degree glide path only makes about a 3 ft difference in horizontal distance at 2 nm (the MAP on the VOR approach) even out at ZULU, the difference is about 13 ft. For that matter the difference between the Slant Range and the and horizontal ground distance out at ZULU is less than 100 ft, which isn't meaningful in the context of navigation and obviously not the source of the difference here.
The orthometric height change was not my point. The distance to the runway threshold is not published in the Philippines AIP, they are numbers calculated by Jepp. The published distance in the AIP for the LOC MAP is 0.92 DME IMA, Jepp published 0.9. In the AIP the MIA DVOR/DME is 193.66M FM RWY06/24 CL and 117.83M FM extended RWY13/31 CL.DME24 is 125M right of RWY24 & 410M FM RWY24 THR.
In the profile view you need to be aware of the rounding and the source of the data.
Originally Posted by
A Squared
As far as your distances based on the geographic positions, that all checks. However. you're still going to be above the glideslope. Not a lot, and not too hard to push it over and catch it, but you aren't approaching it from below. The GS altitude at ZULU is, like I said earlier, going to be 3316, and as you approach ZULU, you're going to be at D10.3 MIA, still within the 3500 MVA sector, and still not established on a published portion of the approach (until passing ZULU). As AtoBsafely noted, higher than standard temperatures which are the norm there will place you even further above the GS. So, you're either going to have to capture the GS from above, or after crossing ZULU, descend rapidly until below the GS, then capture it from below. I'm not sure that the latter is really "better" than the former in any meaningful way.
.
The numbers I did above were just quick and dirty calculations, accurate calculations. MIA to ZULU 10.3 nm (19132.9166 m).
First Station : IML DME
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LAT = 14 30 39.63300 North
LON = 121 1 34.25900 East
EHT = 15.2400 Meters
Second Station : ZULU
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LAT = 14 35 31.60000 North
LON = 121 10 35.44000 East
EHT = 1066.8000 Meters
Forward azimuth FAZ = 60 59 59.4440 From North
Back azimuth BAZ = 241 2 15.4164 From North
Ellipsoidal distance S = 18520.1913 m
Delta height dh = 1051.5600 m
Mark-to-mark distance D = 18551.5845 m
Now by using the inverse of that projecting out where the intercept will be on an azimuth of 60 59 59.4440 from the IML DME at 3500 ft (1066.8 m), 10 DME (18520.01 m ) I get the glidepath intercept to be at N 14 35 31.10177 E 121 10 34.51561, that is 31 meters east of ZULU. Most aircraft will capture a GP within 150 ft.
First Station : INTERCEPT
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LAT = 14 35 31.10177 North
LON = 121 10 34.51561 East
EHT = 1066.8000 Meters
Second Station : ZULU
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LAT = 14 35 31.60000 North
LON = 121 10 35.44000 East
EHT = 1066.8000 Meters
Forward azimuth FAZ = 61 2 14.8453 From North
Back azimuth BAZ = 241 2 15.0782 From North
Ellipsoidal distance S = 31.6228 m
Delta height dh = 0.0000 m
Mark-to-mark distance D = 31.6281 m