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Localizer range limit? GP antena elevation?

Messages
757
Country
netherlands
Hello,

I am writing some procedures for AIRAC format of PMDG, specificaly IGS approach for Sion LSGS. I use the scenery from FlyLogic.

I have found that this scenery only gives me G/S signal about a mile past FAF, thereby effectively negating the possibility to fly the approach by instruments - at least that is the case in PMDG NGX.

Since I was already playing with navaids in the AFX file to correct old frequency and to reposition DME, I tried to increase the range of "ILS" installation, however, ADE will not let me put any more than already preset 30nm.

Is this a compiler limit? Is it possible to circumvent?


Also, in Sion, the GP antenna is positioned in significant distance from the runway, in fact, over 3 km. The elevation is only marginally different (tens of feet), but I would ask anyway - I suppose FS will calculate beam from defined airport elevation, is this true? Could it have any effect on range, or in terrain clearance? I did find myself uncomfortably close to the mountains on said approach, after hitting the G/S, even though terrain separation might be guaranteed.

Thank you for any insights.
Peter
 
Messages
8,893
Since FS does not know what a IGS approach is that is a LDA approach with GS to RWY 25. The GS is set so on approach the plane does not descend until clearing the 12000 ft mountains.

Once your plane reaches the GS the approach becomes visual using the PAPI. FS did not place this approach in the database and I would have to see the approach plate for any further explinations.

30 DME for the Loc and GS is a FS code. In most cases that will only be 23-27NM based on airport location.
 
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Messages
757
Country
netherlands
Hello Jim,

I understand how IGS works and how is it simulated within FS.
If there is an internal FS limitation on range, that is too bad, as it renders the approach correctly unflyable. Platform altitude is 17 000, with possible step down to 16 000. Intercept is at about 26nm DME. However GS does not become alive until about 15300, a further mile down.

Since approach without G/S is prohibited, I guess that puts us to a problem - we can not fly the approach correctly.
 
Messages
8,893
Hi Peter

In most cases GS trails Loc by about 3 NM. I see this at most airports where Loc comes alive at 26 and GS at 23NM.

Is there a IGS chart somewhere on the net for this runway? I would like to look at it.
 
Messages
1,268
Country
us-hawaii
I played with the stock LSGS and agree, best I could get was ISI D23.4 @14,500 ft. But from there things seem reasonable:

D19 chart 11790 observe 11750
D14.2 chart 8720 observe 8640
D7 chart 4120 observe 4050

From a standpoint of writing approach or FMS code, though, I don't think it matters. I think you could still use MASEB as the FAF, though don't know how AI aircraft would like it. Jim would probably give some hints.

scott s.
.
 
Messages
8,893
Peter

I played around with the approach also.

I set the GS to 6 degree, added a DME, set 30NM on the localizer and tweaked the position slightly. The best I could get was the GS came alive .2nm past ALETO at 16000 ft.

Setting Appr immediately and I was able to capture the LOC and GS.

At D7.0 ISI (4120) I flatten the glidepath back to 3.5 degree and made the final appr per the insert.

The only way to get the GS to come alive sooner is move the GS further back from the airport.
 
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