OK so the KAP140 has the analog roll steering input too.
The KLN90B I have has turn anticipation which work relatively well but its not computed bank angle but averaged. Even if the KLN94 would enable roll steering I don’t think it would offer significant improvements since it doesn’t support interpretation of the more complex path and terminators used for SBAS in the final approach segment.
The KLN94 + simple autopilot will fly, in NAV mode, any track sequence which the GPS can handle and display.
Perhaps sub optimally but mostly just fine.
This is from the newer 172 poh:
At 172R serial number 17281174 and On, automated Roll Steering
functionality has been added to the Bendix/King KLN 94 GPS
Navigation System and the KAP 140 2 Axis Autopilot System. Roll
Steering coupling between the GPS and the Autopilot provides area
navigation with automatic course changes at flight plan waypoints
similar to Flight Management System (FMS) operations, but without
vertical navigation capability. The Roll Steering function is similar
to “turn anticipation” for the autopilot.
At the noted serial effectivity, the KLN 94 GPS (ORS 03 or later)
has an added Roll Steering signal output. In order for the GPS Roll
Steering output to be utilized, the KAP 140 Autopilot (-7904 or later)
has an added input for the Roll Steering signal and additional
system wiring has been added to the airplane to connect the Roll
Steering signal output from the KLN 94 GPS to the Roll Steering
input of the KAP 140 Autopilot.
To my understanding roll steering is beneficial when on an RNP approach based on ARINC 424 path and terminators. The older GPS don’t support the more complex path and terminators. On the SN3500 roll steering is enabled in HDG mode by pushing the HDG knob. Latest is ARINC424 is version 22 I believe. Older FMS cant digest that
The KLN90B I have has turn anticipation which work relatively well but its not computed bank angle but averaged. Even if the KLN94 would enable roll steering I don’t think it would offer significant improvements since it doesn’t support interpretation of the more complex path and terminators used for SBAS in the final approach segment.
Ha 
I meant 2001.
Peter wrote:
one of the last TBs made, in 2021
So at last you managed to have Daher put together one for you from the old parts in stock ;?
I suggest you contact Avionik Straubing and see if they have access to the upgrade software. They are one of the very few remaining BendixKing repair centres in Europe.
OK, I will check if it in operation if the wiring 
exists. However when purchasing a used KLM 94 it´s not a problem to upgrade the software from V.-01 to V. -02.
It can be perfomed with the Data Loader program which I have to update the databases.
Could anyone help me out in getting the p__/n 222-30469-1001 = KLN 94 CD-ROM__ for Software 0201?
Finally it must be checked it has perhaps to be switched on in the Maintanence program of the KLN 94.
I have never met anyone who really knew if he had this connected, let alone anyone who collected flight data on the turns. I suspect it never was connected.
The KLN94 – KFC225 always performs “steering”. Each time the KLN94 switches to the next track section, the autopilot follows it. The KLN94 has a setting called “turn anticipation” and this works pretty well. See track examples here.
Proper roll steering (via ARINC429) transmits roll angle commands to the autopilot and this works better. See e.g. here here and here.
As regards who can do the firmware upgrade, a Honeywell dealer should be able to do it. However I suspect most of them have chucked their HBK gear in the bin years ago.
The KLN94 MM is here. It makes various references to the roll steering output. The steering output is here
and I see no reference to it being present only on some models. I suspect every KLN94 has it. @wigglyamp will know, if he is still posting here.
Well I „thought“ it would operate roll steering, it‘s one of the last TB20s, s/n 2205 of it‘s kind still equipped with a KFC225 🤔, but not sure how to check this out as you mentioned most of the a/c owners would not know about that feature and how to check the roll steering commands being executed to reassure roll steering works as it should?
I am not sure you can easily tell.
AFAIK the KLN94 “roll steering” works only with a KFC225.
What year and S/N is your TB20? The Socata wiring diagrams contain a S/N range. I am fairly sure that Socata never connected it up, because my TB20 is one of the last TBs made, in 2021.
