Standard (29.29/1013) Altitude Encoder Output

[schumaku]

We are - just like plenty of other EFIS users before here in the forum - looking for a option to always supply pressure (standard, 29.29/1013) altitude on the Encoder serial transmit (EFIS DB25 pin #13, GND #21), regardless the baro settings.

Assuming the displayed altitude is software calculated based on the baro settings, it should not be that difficult to maintain both altitude numbers in the system.

Here what the EFIS-D100 Installation Guide, P/N 100478-000, Revision E, For use with firmware version 5.0, says:
http://www.dynonavionics.com/downloads/Install_Guides/EFIS-D100%20Installation%20Guide.pdf

"Altitude Encoder Wiring

The EFIS-D100 outputs its altitude measurements in one of four standard serial
outputs and is readable by many modern transponders. The EFIS-D100 will function properly whether or not this altitude encoder functionality is used. To use the EFIS-D100‘s altitude encoder functionality, simply wire the 2 encoder connections (GND and Encoder Transmit) from the DB25 connector to their respective connections on your transponder.

Per ATC/FAA requirements, the serial encoder output of the EFIS-D100 reports pressure altitude, which, by definition, is indicated altitude when the baro is set to 29.92. So, when you set your EFIS-D100‘s baro adjustment to 29.92, its indicated altitude will match the altitude that is being reported to your transponder"

The actual implementation does make the encoder output of the EFIS virtually useless. When flying in lower airspaces, CTR, ATZ or similar, all traffic has to switch to QNH - without interfering or falsifying the transponder altitude - especially in the Mode S environments. Currently, the only work-around is to install an additional, independent serial encoder, adding weight and unwanted complexity.

Thus, we kindly ask Dynon Avionics to add a set-up option (not to change the default or previous behavior), allowing to set the encoder serial transmit on pin #13 to standard 29.29/1013, regardless the baro settings.

[edit]
Or can Dynon Support confirm - regardless various postings in the forum here - the encoder altitude is always standard based on 29.29/1013 and does not change when altering the baro scale on the front end?
[/edit]
Greetz,
-Kurt.
Experimental Aviation of Switzerland
SportAviation of Switzerland
Czech Sport Aircraft factory representative for A, CH, D

 

[ben.fitzgerald]

I'll agree with this - should be a simple software change to do, and otherwise risks annoying air traffic controllers (very busy air space here in Europe), and also even worse risk of compromising flight safety and vertical seperation if the wrong settings are used....

Please look at this request urgently - currently the only safe solution I think is to use a separate alticoder - especially if others fly the plane.

Regards
Ben

 

[dynonsupport]

The encoder output ALWAYS outputs at 29.92/1013, just like you want. It always has, from the very first D10 shipped back in 2003.

You're mis-reading the statement from the manual. If you read the statement more simply, it might make more sense:
"Per ATC/FAA requirements, the serial encoder output of the EFIS-D100 reports pressure altitude"

It's saying if you want the displayed altitude to match the encoder out, you must manually set the QNH to 29.92, because the encoder out is always at 29.92. Since the encoder is always at 29.92, if your QNH is anything but 29.92, they won't match.

We are not saying it only outputs when you are at 29.92 or anything else like that.

We have this statement in the manual because a lot of people called us and complained that their Garmin 327 was saying 2200 feet while the altimeter said 2400 feet. They were of course at a different QNH, but they had no idea transponders always output at 29.92.

Anyway, it does what you want, so no changes needed.

 

[schumaku]

Thank you very much for the clarification. Issue closed.

Cheers,

-Kurt.