My setup for the Citation is Garmin ADC units which are converted to analog signals by a Skylight 602 box. It takes in ARINC 429 air data from the Garmin system, plus ALT, VS, and IAS hold discrete inputs, and produces the necessary analog signals for the SPZ autopilot (technically, for the FZ-500 flight director box).

The analog outputs are:

IAS: 11.11 mV per knot
VS: 0.5 V per 1000 FPM
ALT for FD: 0.75 V at 0 MSL plus 0.2 mV per foot
ALT for AP: 2.5 V at 0 MSL plus 0.2 mV per foot
ERROR (ALT hold mode): 10 mV per foot
ERROR (VS hold mode): 1.0 V per 1000 FPM
ERROR (IAS hold mode): 35 mV per knot

This allows removal of the original Honeywell ADC box entirely.

This is the Columbia/Blackhawk STC. The JetTech STC retains the Honeywell ADC from what I have been told.


Or find an adapter box that converts the Garmin ADC data to the signals the autopilot wants.

All of this would be much more elegant with a GFC 600 (or some other digital autopilot like Genesys STEC 5000).

The FAA roadblocks to getting AP STCs is overall negative safety. APs seems to be so hard to get approved.

Mike C.

Wow - being able to retrofit PL21 on II's (maybe even Evo's) is a HUGE deal.

I was thinking RVSM is something that could be reasonably accomplished, EIS maybe, and an autopilot a pipe dream. My opinion is likely colored by the MU-2/Garmin autopilot saga.

Someone mentioned servo's before...can't imagine the pitch servo could be Garmin replaced...

Skylight was my go to back in the day for interface boxes. I'm not sure if they have developed anything new since Al died.

They were hands down the quickest from spec to finished product.

Skylight was my go to back in the day for interface boxes. I'm not sure if they have developed anything new since Al died.

They were hands down the quickest from spec to finished product.

Just for curiosity, what does the Skylight box do that the GAD43e doesn’t/can’t? That is also a digital to analog conversion of at least some things.

So conceptually similar, just “needs more”? Wonder if a second GAD43e could be set up to do the other stuff. Obviously, theoretically anything is possible given enough time and money.

Latest I heard is that they are basically closed. I think their assets are for sale. The wife was running it and maybe she's gone or retired.

Also, I heard there is an IS&S box that can do basically the same thing and that Columbia/Blackhawk is working to get that approved under their STC.


Maybe, but the quality of their production was suspect in recent times.

I'd be very happy to get rid of all the little adapter boxes and go digital to digital.

Mike C.

The Skylight does the exact right digital to analog format conversion from the ARINC 429 messages to the analog inputs the SPZ requires.

The GAD 43e might be lacking in both the requires electrical interfaces and the firmware to do the conversion in the right way. It seems focused on attitude and heading signals, not air data.

It doesn't matter which box does it, you just need a box to do it.

Mike C.

This is the same sort of thing that is keeping Garmin EFIS panels out of Ultra, Encore, Bravo Citations. They have a Honeywell Primus 1000 setup where the AP is integrated into the screen controllers. You can't pull the screens and not have another autopilot option.

Garmin is shut off from literally tens of millions of revenue without an autopilot option for those aircraft, and there is considerable demand to pull the Honeywell Primus 1000 system out.

I don't understand why they are being so slow about this. This should have been priority number 1 in the autopilot program.

I get the feeling Garmin management is not understanding how AP approvals drive the rest of their revenue and the AP programs don't look like money makers to them. But that is totally wrong.

If they had an AP for the entire Piaggio line, I bet in 5 years, every decent airplane is converted. It will become expected in the market to have been Garminized. Without a fleet wide AP, however, all that revenue is locked out.

Mike C.

I can believe that. It's the analog Garmin<>Collins interface that I am less impressed with. Love the Garmin avionics. But paired with Garmin EIS and digital Autopilot it'd be way better.

The “whole panel” approach can be done and in the Piaggio it could add some value.
We already know the Citation CJ2 Proline 21-Universal FMS is next in line—supposed to be complete mid next year. Full Garmin+EIS system. Joey from Garmin is updating progress over at the CJP forum.

I would expect the Piaggio and the Honeywell Citations are a long way off. It just takes a lot of time.
Garmin is not an aviation company.
55% of revenue is outdoor-consumer. Marine is 20%. Aviation is less than that—16%.
Follow the money.

An IS&S synthetic vision stc for the Rockwell Collins’s Piaggio-II’s would seem like a good compromise to add value. The proline system gets the job done and some seem to prefer it even with the well known negative trade offs.

As evidence that is probably true... I offer the following pages from the APS-65 Install manual, which suggest that the APC-65A variant (which is installed in the Piaggio) has a digital bus for ADC data.

I don't know if the G600 can output the exact data stream needed - "CSDB"? - but it implies it might not be too difficult, i.e. maybe just software, if any change required at all.

That would be an elegant half solution for sure, though I suspect this would not permit en route vnav.

What I don't understand though is why the RVSM curves are even necessary. I'm assuming that the Garmin transponders we all have transmit altitude information sourced by the Collins ADC, right? Othewise, we'd be getting complaints by ATC ("What the eff are you doing at 36,140?!")
So you'd think the G600txi could simply accept altitude input the same way rather than from a Garmin ADC?

Ed

That would be an elegant half solution for sure, though I suspect this would not permit en route vnav.

What I don't understand though is why the RVSM curves are even necessary. I'm assuming that the Garmin transponders we all have transmit altitude information sourced by the Collins ADC, right? Othewise, we'd be getting complaints by ATC ("What the eff are you doing at 36,140?!")
So you'd think the G600txi could simply accept altitude input the same way rather than from a Garmin ADC?

Ed

CSDB - "Commercial Standard Digital Bus" formerly "Collins Standard Digital Bus"

It is RS-422 (which is just RS-232 serial but with differential signaling for better noise immunity) running at 50 Kbs.

The protocol has a leading address byte and then data, so kind of like ARINC labels.

I don't know if the Garmin stuff can output ADC data on RS-232/RS-422 or not, or can do the CSDB format. This is likely within reach with some software and maybe an electrical format conversion RS-232 to RS-422 which is trivial. Whether Garmin would do it is another question, of course.

The only RS-422 in my setup is between the GRS 79 AHRS and the GMU 44B magnetometer.

Mike C.