D-shaped shaft or splined shaft have clearance that has to be taken out somehow. Usually on a D-shaft there is a setscrew set against the flat. Splines are a poor choice for reversing loads. If not pre-loaded, they fret (particularly in high-vibration environments such as aircraft,) producing fod and increasing the clearance and eventually leading to a large amount of backlash.
Groooan- I was trying to give examples of well proven methods of joining shafts to gears and other things, and not try to do a detailed design- redesign.
As to failure of shaft or AOA vane, normally the counterweight will respond to gravity and point straight down. I would guess it is possible for a design to say if pointed straight down- absent other issues-signals , the sensor attached would give either a plus or minus AOA indication. if the sensor is detached an internal or designed-in weight could do the same thing and return a signal saying level flight.
And as to attachment and fretting-- locking tapers on shafts and fasteners have been used for decades- they do not slip, fret, or get pulled out easily - check standard machine tool cutter attachment methods or look up ' Taper-lok ' fasteners used in aircraft industry for over 50 years.
MY point is and was - IMO- the AOA sensor needs a more robust mechanical design instead of the flat plate and spring design methods as used on 1920's biplanes used for airspeed as on the Travelair ..
