ARINC 424 Back Course Format

[mbushaw]

We are trying to get a back-course localizer working on a sim. We have tried Phoenix and Reno airports. GSD is from Jeppson circa 1994, in ARINC 424 format.
Does anyone have a breakdown of the 424 format describing what each character string is? I've found some online at avia.transas.com/eng/specific.htm, but nothing there indicates that an ILS would have a back course. The back course runways are listed as GCA, no Localizer info in our GSD.

Thanks for any ideas-

[bluesman]

mbushaw,

What's the make, model and year of your sim.

Also, do you have Jeppview?

www.airnav.com gives good info on airports.

You mentioned that the runways are listed as GCA. Is this in your GSD records or what you found online?

I have some info on Arinc 424 formats I'd be willing to share. Just let me know specifics.

The backcourse info is part of the Facility Characteristics field in the LOC/GS record, bits 27-32.

Char 1 : Voice Ident (Y - Yes).
(N - No).
(U - Undefined).
Char 2 : Blank.
Char 3 : Backbeam (Y - Usable).
(N - Unusable).
(R - Restricted).
(U - Undefined).
Char 4 : DME Location (L - Localiser).
(G - Glideslope).
(or blank).

Send me a privvy-post if you need more info.

[mbushaw]

Hey Bluesman- Thanks! I think this may help us.
Sim Info-
Link MD-82 MST, 1990 vintage originally built for SAS.
No Jeppview
GCA in our output (in the source, that I believe is from a Jeppson disk, they are just listed as Runways with no Localizer association, as it should be as there is no localizer).

Looking thru the NAV programs simulator source I see there is mention of a LOC Backbeam Suppressed flag, so I guess if they have a flag to suppress, there must be a way to activate back beam. Haven't found the bit of code that would toggle this flag yet.

[bluesman]

I'm a bit rusty on the older link machines. You should have some sort of GSD editor. That would be my guess where to suppress/enable the backbeam. I'll ask around.

I'm sending you an email

[mbushaw]

I'm a bit rusty on the older link machines. You should have some sort of GSD editor. That would be my guess where to suppress/enable the backbeam. I'll ask around.

I'm sending you an email

Should have lots of things that just aren't there!
We have to directly edit the source/filter for the locations we want (memory limit)/compile (two to three passes depending on what you are changing) to make changes to GSD.
At least that's what the notes we have say. There may be an editor in there, but there is no documentation for it.

Anyway, I think we are on the right path, thanks to your hints above!
Will let you know how it turns out.

[guest]

In case in helps...

The backcourse available/not available should be a bit in the misc. field. You should have a source text file (.jcl) for each ndat file.

[mbushaw]

Thanks 'Guest'.
This machine uses an Intel Multibus II Unix 'PC' to store / develop software. Once compiled it is transfered over to a 286 Intel IRMX 'PC' via ethernet. That box then is able to load the On Board Modules (more Multibus II computers) with the real time load via ethernet. All the On Board computers stay in touch via ethernet.
Anyway, the GSD source on the development computer is in ASCII (actually very easy to read). The format outline is ARINC 424. So unless one has the special ARINC decoder ring, there are many fields that are impossible to decode. We were able to follow the hint from Bluesman above to fix this problem, and have now moved on to other GSD updates (one thing leads to another. Give them back course and next thing they want DME for cripes sake!).

[Pioneer]

Just to let you know you can buy the ARINC 424 spec from ARINC for about $250 USD, you can even download a PDF copy. The link is https://www.arinc.com/cf/store/catalog_detail.cfm?item_id=609

[guest]

Well, let me just reach in my pocket here and ..... $250.00 BUCKS, WHAHHHT!
Is ARINC run by a pharmaceutical company?