Is it logical to "assume" that if you have a GAD42 and a 530W that you would have GPSS Roll Steering? However, there is NO GPSS/HDG button so how would you activate it? I know in NAV mode, it does not activate roll steering.

Could it have been wired to push NAV twice (I haven't tried this).

Any other ideas?

OK, I'll try to simplify the question, Does the GAD 42 offer GPSS to an autopilot and if so, is there a separate GPSS/HDG button or some other way to activate it?

Yes it does. And it if it is wired correctly the Roll steering will be active when the flight director is in the NAV mode and you do not have an ILS frequency tuned, or an active GPS Approach.

There should not be a separate GPSS switch, the flight director computer will take the roll steering directly from the GAD42.

https://www8.garmin.com/specs/gad42.pdf

ARINC 561 format analog roll steering output for use with flight control systems

Seems so. I think this means the GAD 42 produces the simulated heading bug signals to control an AP in HDG mode so it does GPSS.


There has to be a switch somewhere that you use to choose between the heading bug and GPSS.

This is not built into the GAD 42 as far as I can tell, it is literally a switch that moves the AP signals from heading bug to GAD 42 GPSS output.

Mike C.

That's the issue with these Citations, is everyone is different. The three planes I fly offering the following:

1) No button, GPS steering off the NAV AP mode
2) GPSS/HDG button, GPSS when in HDG AP mode
3) My current airplane, has a GAD42, no button and apparently no GPSS.

The issue is more with installers than the Citations. The ARINC 561 (roll steering) output is supposed to be connected to the LRN (Long Range Nav) input on the autopilot. The connection isn't called out in the manual IIRC, so it gets missed quite a bit.

I have a similar setup in my mu2.

There is a gpss indicator that tells u the boxes are getting signal.

Use cdi on gtn750 to select between nav or gps. When the AP is in gps mode it takes whatever the 750 is outputting and sends to flight director. Much simpler than a separate heading/gpss button imo. Flies beautifully

The roll steering input to the flight computer uses the roll steering valid from the GAD42 to turn on the input, no switch necessary or desired.

Anyone as smart as Terry or Ryan in FL to fix this wire; you guys need a FL vacation to tune this bird up?

I think I'm going to put the following in:

1) Fix GPSS wire per Ryan's suggestion.
2) Flightstream 210
3) Remove clock and install a USB outlet
4) hardwire a GDL 39

With ADSB, WAAS and XM I think this will pretty well equipped legacy Citation with twin 530ws.

On the citation ii I fly, the 530w drives the nav mode unless you have vloc selected on the 530. Both 530 units should have a gad 42 I believe.

I’m sure you’ve done this, but make sure on the autopilot controller it’s selected on the correct hsi. You could even try using the nav mode off the number two hsi.

Also, I’m not sure if the clock is required equipment on the MMEL or MEL, but might want to check.

Yes, there are definitely 2 GAD42 circuit breakers. I think the clock on the transponder is perfectly legal. I just can't imagine they didn't wire this thing up for GPSS; I have to be missing something.

GDL39? Why not a remote mounted GDL51/52?

Would love to help and see the bird. I might be heading to Simcom in the next few weeks.....

Just fixed this problem on a citation 650. Many operators told me this is how the plane flies and you wont get more than 17 degrees bank.......problem was bad altitude signal from the ADC. Autopilot went into bank limit cause it didnt know the aircraft was below altitude. If you cant find the problem, verify the original altitude and speed wires from the adc to the flight director and autopilot

No.

I have the same stuff in the Merlin and no GPSS steering.