Decided to take a short tour, hopped in the Cessna caravan, took off normal and then it started :
I engaged the flight director first, aligned the airplane with it (was a challenge since it was bouncing too much due to turbulence), and pressed the AP, engaged NAV mode and FLC.
It seems that it tried to capture the speed using pitch but the flight director said one thing airplane did completely another 
. Then as it approaching the selected altitude of 6000 feed the autopilot just busted tight through it and kept climbing. Tried to select VS to fix the error⊠AP is like NOO ! still continue to climb.
I flew the Caravan before and it was OK, I donât know why it decided not to cooperate today. Disappointment.
I try to understand why MS/ASOBO doesnât use the same Autopilot principal for all the planes ? Isnât it does the same thing just some planes has some different functions ? I donât get it⊠but hope they will fix it. The Caravan is useless unless you hand fly.
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I never, never press AP before having engaged either a lateral or vertical mode first. I usually set, in order, NAV, FD, YD, VS (because I will monitor airspeed) and dial in a climb / descent rate. I will have set a target altitude before all that. Only then, will I hit AP.
Thatâs been my procedure since Launch Week. Works every time. Also, be in a level, stable attitude, Plenty of margin above stall, preferably at a heading less than 15 degrees from desired heading or next NAV point. Donât make the AP work too hard to get you to heading and altitude, that is a recipe for bad AP decisions regarding pitch and bank.
The Tour was the first thing I did after installing USA Update. The above worked like a charm once I cleared 500â and one mile from Stewart threshold. AP took me all the way to DCA.
The AP isnât broken. Based on problems Iâve seen posted, people are engaging AP in non-stable attitudes and/or speeds. Hand fly the course until you are well above stall, in level flight, with plenty of altitude margin to recover. Get as close to base course as you can before engaging a lateral mode. Wait and monitor that lateral Nav is stable and working before trying any Alt modes. Simple.
That is how it should work. I really wish it was that simple, user error causes the problem, if the user does it right there is no problem. Except that is just a convenient fiction. It is something else that is causing this intermittent problem.
Todayâs flight, also in the C208:
Engage FD, HDG, FLC 115 kts. Ensure the FD V is tracked, aircraft is in trim.
Engage AP. (YD is currently inop in the C208.)
Aircraft goes full dive bomber mode.
Disengage AP and FD, aircraft is now significantly out of trim nose down. Recover from the dive.
Do the same thing again, this time trying VS mode at about 1000 fpm instead of FLC
Engage AP, same thing happens. Recover from the dive the same way.
Establish in climb again, 115 kts, in trim.
Leave FD disengaged.
Engage AP. No issue, aircraft flies nicely in ROL and PIT mode.
Engage HDG, FLC.
So, doing it right => suicide dive
Doing it âwrongâ (but IRL a perfectly good way of doing it) => worked perfectly
I have over 2 years of G1000 GFC 700 Autopilot flying on both the Cessna 172 and DA42, and I never had any issues with the autopilot. No matter the sequence it did what it supposed to do. In reality the flight director gives the commands and the AP system job is to follow it nice and easy. If something is not right it should be fixed ! Iâm not going to memorize the enigma code sequence for the AP 
FLC is dangerous in FS, itâs true. Thatâs why I said, VS plus watch airspeed like a hawk. Also, if you make the error of not setting a target altitude before setting a vertical mode, the AP acts upon that to say, oh you want to descend. As the GI Joe Cartoon goes, âNow you know, and knowing is half the battle.â
IRL we should all use FLC. In the sim, FLC cannot adequately manage pitch and airspeed sufficiently. Do not use FLC, at least on the GA Props. Tube and bizjets have to use it for the speed and altitude ranges they operate in, but given everything else thatâs broken in there, who knows?
FD has never been a problem. Iâve followed that sequence for months.
That is not my experience at all. I use FLC all the time and it works just great, on the C172 and on the C208. And of course I set the target altitude first.
The problem is that sometimes, and I have not been able to figure out exactly what causes it, when engaging the AP it dives for the ground. Other times, it works fine.
But one thing is certain: In my experience, whether FD is engaged before AP, and whether the aircraft is following the FD when the AP is engaged, is not in itself a guarantee that the AP will engage successfully.
I too use FLC extensively both in the C208 & the B350. It absolutely works no problem.
The only time I ever get a nose dive, is when I have forgotten to set the altitude selector appropriately.
AP first and then modes, or FD modes first, then engage AP, does not matter. Both methods work, and are acceptable in real life too.
By far the most important thing is to ensure the aircrafts is in trim when engaging the AP. Not just manually following the FD bars if they are selected. Properly in trim. Let go of all controls and make sure the aircraft is steady, then engage AP.
I tried that again. Worked this time !, (I always pres elect Altitude and runway heading bug after engine start).
I wonder why some time it does work and sometime doesnât ? What is broken in the algorithm that it can not follow the same thing all the time ?
Honestly it worked perfectly for me on the first attempt. I expected a CTD or just something not to be entirely right but - alas - it all just worked. 
I tend to find people often donât do the same thing every time, even when they think they doâŠ
Yeah, @CasualClick is reporting great results with the âfollow FD firstâ approach, so that approach clearly works. Yet I have frequently had failures with that method â but not always, sometimes it works for me too. The âengage AP firstâ method seems to work better for me. Both approaches are perfectly valid and both should work.
Obviously, whether it works or not depends on some system state, probably something done differently during the flight as @Norman999933 points out. But I am convinced it is not related to whether or not good real life practices are followed, such as something well-known and obvious like being in trim before engaging AP. It is something sim-specific that causes it to end up in a bad state and decide to dive for the ground.
Using FLC for climb and VS for descent has worked well foe me.
Itâs nice when it works like this. But how do you explain the following (relates to A320neo and Cessna Citation Longitude IFR low-alt from EGBB to EGLL 27R)? You are flying straight and level and have engaged AP for altitude, NAV, and autothrust for 250kts. Everything is stable, you are enjoying the view and thinking about the forthcoming approach. Then you notice the roll of 45degrees while youâve been dosing, the AP has given up and you are headind down and away from the flight plan. You fight for control, fly by hand to the flight plan, get things steady, and engage the various AP controls. But the plane refuses to follow the flight plan. This is what just happened to me, first in the A320neo then the Cessna, as a test. My point is that while it is great when things work right, and some pilots expect too much of the AP through lack of experience, the AP (and other things) do fall over sometimes.