Autopilot altitude manual arming

We didn’t find a correct way to manage dynamically manual autopilot altitude
arming. Currently, the sim always arms altitude so it’s not possible to have a
VS, FLC, or PITCH mode that doesn’t switch to ALT at the selected altitude.
There is a parameter “no_alt_capture_in_vs_mode” in the aircraft config file
but nothing to do that dynamically so implementing a manual arming in an
aircraft is a nightmare. Using slots is not working too because the active
slot value is always copied into the “AUTOPILOT ALTITUDE LOCK VAR” slot 0
variable. The workaround we have found is to set a very high value (ex 99000)
in the “AUTOPILOT ALTITUDE LOCK VAR” but many users complain because their HUD
or other aircraft instrument displays 99000 as the currently selected altitude
in this case. We have also noticed that the “AUTOPILOT ALTITUDE ARM” sim
variable is never set. Maybe a K event that disables auto arming could help or
any other solution allowing dynamic manual arming. The Asobo KAP140 ARM button
is not implemented, probably because of this situation. Thanks for your
feedback about that. This is currently a blocking situation for many aircraft.

@pms50 Presently the way to do this is by enabling avionics managed autopilot
mode. This makes all the mode transitions and simvars the responsibility of
the avionics code. You can enable avionics managed mode by setting simvar
AUTOPILOT AVIONICS MANAGED to true by using key events
go back to normal). This will disable automatic transition to altitude capture
mode. Then, you can write your own altitude capture/arm logic in your avionics
instead. The only caveat is that you will need to write the autopilot state
simvars on your own: while in AUTOPILOT AVIONICS MANAGED they will not reflect
the actual underlying autopilot mode, to allow avionics to “drive” the
autopilot using some underlying mode but “report” whatever mode they desire.
So, in your case, you would write to AUTOPILOT VERTICAL HOLD when you engage
V/S (using the standard V/S key event), then when you detect your altitude
hold conditions, engage alt hold (again using the standard alt hold key event)
and write to AUTOPILOT ALTITUDE LOCK. Again, just to be super clear: the
avionics must manage the sync of the autopilot state simvars on their own
Writing to the autopilot state simvars
does not change the underlying autopilot mode, only using the key events
does. While in alt lock, the same ALTITUDE LOCK VAR simvar controls the
altitude to hold at. There is no change there. Hope this helps! -Matt

Thank you Matt for your answer. I will try to investigate in this way but the
problem is that I have to write all the AP state variables (which ones
exactly, all of them?). This seems to be a huge task because most of the time
we’ll not be in the armed mode so I will have to rewrite by myself all the
mode transitions and simvars. Now, maybe I didn’t understand exactly what the
K:AP_AVIONICS_MANAGED_ON does. Today everything works as expected but this
auto arming that can’t be disabled dynamically. Probably 2 new K events to
enable/disable auto arming would do the job the easiest way (ex
K:AP_ALT_AUTO_ARM_ON and K:AP_ALT_AUTO_ARM_OFF) plus maybe a simvar to get the
current AUTO ARM state.

So I tried with the managed mode but this is definitively not the place in a
gauge to do that (many side effects). This should be done at the autopilot
manager level (maybe by K events as I suggested). Anyway, I was able to
disable auto arming in the WT autopilot manager and that works fine. The
functionality is just missing for the stock Asobo autopilot manager. Hope we
could get it.

Could we get that in SU11?