Good question ... I asked myself the same thing, But I really like this feature... it's much safer (in my view) than to select other modes shortly after take-off. I first use AP only... and the go to IAS+ALT or VS+ALT at a safe altitude
One thing I always wondered about this how APs treat this pitch hold / roll hold mode. When I engage the DFC90, it always has both a pitch and a roll mode. It can never only have one which is different from the S-TECs.
If I don't specifically chose a lateral or vertical mode, then it will use hold mode. Let's say I press ALT, then it will switch to maintain altitude + maintain roll. If I disable it and then press HDG, it will switch to maintain heading + maintain pitch.
So far so good. What I am wondering is why the autopilot does not offer an option to go back from a selected mode to the hold mode. In order to switch from maintain altitude to hold pitch, I have to disable the autopilot and select a lateral mode.
Is there a certification reason for this?
The autopilot will attempt to maintain pitch as it climbs and as a consequence you almost get a poor mans IAS hold. It is certainly better than VS.
Yeah, I can see that probably does work quite well.
The pitch hold mode is more or less required to reach the operating ceiling, because the KFC225 treats the preset VS figure as "plus or minus 100fpm" so if you set +100fpm you might get 200 and obviously the plane won't achieve 200 at near the ceiling. Whereas the pitch hold mode, set at something like 4-5 degrees UP once above say FL150, will get you there.
One day I will discover why the PA46 gets a lot fewer problems with the KFC225 servos 
I also fly with a KFC225 in the Jetprop. Coupled to the Aspen, the GPSS is rock solid, and add in the procedures from the GNSW’s, it is a very capable package.
Travis Holland taught me a neat trick which almost gives you speed hold on the 225.
When climbing, use pitch hold mode rather than VS mode. The autopilot will attempt to maintain pitch as it climbs and as a consequence you almost get a poor mans IAS hold. It is certainly better than VS.
I recall reading this tip in one of your KFC225 blogs as well Peter, but for a different reason. :-)?
I find that I am reducing the pitch angle (via the up down buttons) to maintain airspeed far less then decreasing VS as I used to previously. I still use VS on descent. E
Peter,
It is all about what authority you give to george, the authority to maintain a VS in which case the autopilot will eventually induce a stall or the authority to hold an airspeed, in which case how much of a climb or descent depends on power available. You might not be climbing at a fixed airspeed, but you won't be stalled.
Of course the pitch has to be adjusted constantly with decreasing engine power and increasing altitude to keep the IAS constant.
Yes, that's exactly what I said.
VS tends to fluctuate much more than IAS which is rather sticky (ever seen your ASI needle fluctuate during cruise?). This makes constant IAS a nicer ride than constant VS.
IAS is basically a constant pitch setting (at constant power)
I don't think it is implemented that way.
With IAS hold, the pitch is the primary target (the inner control loop) and the IAS is the secondary target (the outer control loop).
With VS hold, the pitch is the primary target (the inner control loop) and the VS is the secondary target (the outer control loop).
Every autopilot has a pitch-hold mode - called AP. That runs just the inner loop.
Cobalt, nice idea, but the way Achim does it (and me too) is just as nice... you see the CHT is rising twds 380 you just increase the speed a bit. Maybe sich a setting would be too obscure for many users and if they forgot what the setting they might not have the full climb power... and if you fly twds a mountain the last you should care about is the CHT ;-)
The DFC90 has a stall/envelope protection anyway. I have only tested it in VMS. I am not yet such a great IFR pilot I but I can imagine that the envelope protection can save your day in IMC, because it will simply not let the autopilot stall the plane.
I tried in VMC. Pulled the power back (no flaps, 50 flaps, 100 flaps)... and shortly before the stall the DFC90 gives you a warning both on the PFD and and aural: "Underspeed" (Of course lacking an AOA probe it has to use the speed, but it works).
What's also very nice with the DFC90, if you have the "Flap Wire" installed: It flies the plane nicely with full flaps. I am not sure yet how safe that is, but at altitude it works perfectly.
