Garmin 430W Baro Corrected Altitude

flickroll · #1 03-06-2010, 07:23 AM

I am working on a panel upgrade that will have among other things an AFS 4500, G430W, GTX327 (or SL70), and the AFS ARINC adapter.

The G430 needs baro corrected altitude for RAIM prediction. The AFS instructions are not clear on how to do this.

I think you could do this one of 2 ways:

One method is to feed the AFS encoder RS232 TX to the 327 RS232 RX (this happens anyway - required for altitude info to the 327), then use the 327 RS232 TX to feed the G430, using Garmin 430 RS232 Channel #2 (#1 is used for fuel data straight from the AFS EFIS). A question: does the AFS unit send baro corrected altitude, or pressure altitude? I would think it sends pressure altitude since the 327 needs pressure altitude information.

Another method is to split the AFS encoder 232 TX to feed the 327 and the 430 separately. With this method you'd split the cable leaving the AFS unit into 2 wires, one going to the 327, the other to the 430, again to Garmin 430 232 port 2.

The drawback I see with method 1 is if your transponder goes belly up you will lose the altitude info to the 430. May be a rare event, but it is a possibility. Another drawback with method 1 is I don't think it would work with an SL70. It does not output Icarus altitude which is what the 430 is looking for.

I think method 2 is the preferred way to go, although I am not clear if AFS sends baro or pressure altitude...

In any event, for folks with AFS units and a 430, how did you accomplish this requirement? One of the 2 methods shown above, or something different?

Thanks

NDrv8r · #2 03-06-2010, 07:54 AM

all encoders send pressure altitude. This results in everyone else depending on the altitude output (ATC and those with tcas) getting consistent information not affected by baro set knob.

flickroll · #3 03-06-2010, 08:04 AM

That's what I thought...

So how does one get baro altitude to a 430 from AFS? Or GRT? OR Dynon?

Mel · #4 03-06-2010, 08:59 AM

I don't know of any reason that it would need "corrected" altitude.
Everything is set up to use "pressure" altitude.

w1curtis · #5 03-06-2010, 09:06 AM

The 430 needs Pressure Altitude, not baro correct altitude for RAMI/FDE.
For the TAS calculation functions that require altimeter setting, it prompts you for this on that page.

flickroll · #6 03-06-2010, 09:23 AM

Quote:

Originally Posted by w1curtis

The 430 needs Pressure Altitude, not baro correct altitude for RAMI/FDE.
For the TAS calculation functions that require altimeter setting, it prompts you for this on that page.

Well I'll be switched... I found this in the G430W manual:

"Barometric altitude is not required by the 400W Series unit to meet the requirements of of TSO C146a"

I believe it IS required for non WAAS 430's. Thanks for the clarification.

W1Curtis, how did you connect your encoder to the AFS unit? By means of my method 1 or method 2?

Thanks

mburch · #7 03-06-2010, 09:32 AM

Don't forget you can use ARINC 429 for this as well.

mcb

Garage Guy · #8 03-06-2010, 09:40 AM

Quote:

Originally Posted by flickroll

I believe it IS required for non WAAS 430's.

That would make sense. It (baro corrected altitude) is also required for our Apollo GX60; when enabling an approach, it prompts for the current altimeter setting. Now, our Rocky Mountain Microencoder is configurable to send baro corrected altitude data on one of its outputs (it sends ordinary pressure altitude on the other, to keep the transponder happy). Routing that to the GX60 means you can always tell the GX60 the current altimeter is 29.92", which is done with just a single button push; very convenient.

That a WAAS GPS has the accuracy to supply in effect its own altimeter setting is nice. But if the AFS EFIS can't be configured to provide corrected altitude on one of its serial outputs though, that would make it less than convenient for interfacing to these older non-WAAS units.

--Paul

flickroll · #9 03-06-2010, 10:16 AM

Quote:

Originally Posted by mburch

Don't forget you can use ARINC 429 for this as well.

mcb

Except that according to AFS they do not send altitude data via ARINC. Wish they did as it would allow for more installation options.

flickroll · #10 03-06-2010, 10:23 AM

Quote:

Originally Posted by Garage Guy

But if the AFS EFIS can't be configured to provide corrected altitude on one of its serial outputs though, that would make it less than convenient for interfacing to these older non-WAAS units.

I'm working on getting an answer to this. If AFS does not send baro altitude on Serial 1 then I don't think it is available. It is not available on ARINC, and obviously not on the serial encoder output, so that leaves serial 1 as the only way to send it. I have a 430W so it won't be an issue for me, but as you said, it would be an issue for those with non WAAS units. That installation would require a periodic manual barometer entry.