Interfacing 3400sEE with S-Tec 30 AP

I have a S-Tec 30 AP with GPSS which is nicely driven by my 420W.

I'm have already installed the switch to allow the 3400 and Garmin 420W to drive the AFS Pilot when it is installed.
The output from the switch serves as input to the GPSS converter on my S-Tec 30 and that part seems to work well with the switch in the 420 position.

I have Port 1 set up as AVTN/ARNAV
Port 2 is disabled
Port 3 is SL30
Port 4 is ARINC
GPS/NAV1 data source is serial4
GPS/NAV2 data source is serial3

When I run the diagnostics for the ARINC module - it detects my GPS but not the VOR - expected as I have a 420W which doesn't have the VOR built in.

I am still ground testing and have not finished installing the magnetometer.

When I switch over to the 3400 source for the autopilot input - it acts as though there is no input at all.

Is it possible that the missing magnetometer prevents the 3400 from sending signals to the S-TEC 30's GPSS coupler? It would make sense as a safety feature. The 420 works fine so I know the logic is set up correctly.

Any help is appreciated....even tell me to finish the magnetometer and try again....which is my current plan.

Ralph Capen

What source do you have the AP LAT set to in the EFIS?

Do you know what ARINC labels your S-Tec 30 is expecting?

AP LAT is set to HDG - but on the screen it has a yellow border.

The S-Tec 30 is working properly with the 420W settings required by the AF ARINC Adapter (In1 low honeywell, In2 high off, out GAMA429, SDI common, and VNAV enable labels) and since pins 46 and 47 from the 420W are connected to both the GPSS and the AF ARINC module. Since the AF ARINC module sees the 420W - I'm thinking the settings are correct for the AF ARINC module. Since they work correctly for the GPSS direct connection with the 420W, I'm fairly certain the labeling is correct.

The S-Tec 30 manual only specifies ARINC 429 low speed or GAMA ARINC low speed - it does not reference labelling.

Again, since it is working from the 420W, I think the settings are correct.

It is my understanding that you are switching an external switch that then routes the AP ARINC wires directly from the 420W to your S-Tec. When you switch the external switch so that the S-Tec ARINC wires come from the EFIS this is when you have a problem, is this correct?

Will the S-Tec AP follow the EFIS when the EFIS setting for AP/FD is LAT NAV and your external switch is selecting the EFIS as the S-Tec source?
If this does not work then the S-Tec must be expecting an ARINC label that the EFIS is not sending.

Correct to the first question - it is actually the switch that is called out for the AF Pilot installation - wired the same way.

I haven't tried the LAT NAV setting.

Also, I am doing these tests on the ground, in the hangar - I haven't tried this in flight...yet.
One of the things that might be causing the issue is S-Tec's requirement for a speed indication in order to execute GPSS functions - on the ground it doesn't exist. Does the AF ARINC box send out a airspeed message as part of its output?

We do not send out any airspeed labels, try it in NAV mode on the EFIS.

Have you installed the latest software 8.6.22 and selected STEC for the autopilot type in admin settings?

I have the latest software - I'll look for the STEC selection in the admin settings - thanks!

I changed the AP type to STEC - seems to work properly in both NAV and HDG modes. Thanks!