Usually pressing the autopilot disconnect button on the yoke overrides the envelope protection. But only for so long as you keep it pressed.
@huv thank you it would be great if someone might post what the manual says on supplemental flight training and the operational limitations.
I recently started instructing PPL with a student on his own C172 with GFC500 and AoA indicator. I believe there is no input from the AoA to the AP but will check.
During stall exercises the student was fighting the envelope protection system, but I might not have realised that at once had it not been for the trim wheel moving at the same time. I had forgotten about the full-time protection. Then we pulled the AP circuit breaker and had to live with no electric trim, and we had to remember to re-engage the autopilot system when airwork was completed.
We are developing a new checklist after the airplane’s avionics upgrade anyway, and handling the autopilot system should definitely be included.
I found this but have not gained access yet:
Use of Garmin Autopilot Envelope Protection System for Simplified Vehicle Operations in General Aviation
by Stephen Sullivan
A thesis submitted to the College of Engineering and Science of Florida Institute of Technology
in partial fulfillment of the requirements for the degree of
Master of Science in Aerospace Engineering
Melbourne, Florida
May, 2020
Do the digital autopilots provide real AoA?
Most not and they don’t need to, AHRS, gyros and Pitot-static is sufficient for day VFR.
In the absence of AoA vanes, auto throttle and stick shaker/stick pusher am guessing the envelope protection has its own envelope protection? ie the autopilot has to be disconnected below certain speeds and heights?
No, that is why the pilot has to monitor, which means PIC has to be absolutely clear on what the ESP does.
Does it have degraded functions alerting the envelope protection is no longer operating?
No, it is not airliner protection.
Does the manufacturer provide an outline training syllabus?
The one I know do.
RobertL18C wrote:
Do the digital autopilots provide real AoA? In the absence of AoA vanes, auto throttle and stick shaker/stick pusher am guessing the envelope protection has its own envelope protection? ie the autopilot has to be disconnected below certain speeds and heights? Does it have degraded functions alerting the envelope protection is no longer operating?Does the manufacturer provide an outline training syllabus?
I can’t answer all questions but my understanding SR22 system is disabled bellow 200ft agl, it can be disabled in menu or prolonged press on AP button, annunciation is visible by white marks on PFD near 45deg bank markers (as it’s mostly useful to protect against 45deg banks and overspeed), the training is included in CSIP training packages (if one can afford to cough 12k$), otherwise a read of manual for someone with enough technical background should be enough
I don’t know if it kicks in when ASI is knackered? or AoA sensor fails? and how failed/reliable is split?
As far as flying backside of the drag curve, actually one can disable ESP and fly them very slow, ideally using AoA indicator, say the STOL landing using Synt-Vision display, ahem STALL it on runway with full power in IMC with Flight Path Vector on threshold 
my conclusion on STOL land SR22, is that one is better off pulling his CAPS from safe heights, in comparison, DA40 STOL’s nicely using Synt-Vision data, which is puzzling as DA40 has T-tail with various issues at slow speeds but bizarrely well behaved in the back of the power curve…
PS: there was another safety pilot/instructor looking outside and monitoring rate of climb of ground, after 14 attempts, 7 for each pilot, the last one end up with tiny tail scratch on go-around but all looked safe enough to walk away from an emergency
Peter wrote:
The KFC225, year 1999, is fully digital in that the control loops are in software. And I think some of the other HBK ones from that era are too.
Certainly the KAP140 is digital.
One thing that is many cases is “more digital” toady is the sensor inputs and servo outputs. E.g. the KAP140 has essentially no digital input or output while the GFC500 has (as far as I know) only digital inputs and outputs.
I think “digital autopilot” is just marketing. The KFC225, year 1999, is fully digital in that the control loops are in software. And I think some of the other HBK ones from that era are too.
These boxes sense pitch with an internal pitch gyro – basically a “spirit level” device. There is no AoA input. Does any GA AP have real AoA input?
Do the digital autopilots provide real AoA? In the absence of AoA vanes, auto throttle and stick shaker/stick pusher am guessing the envelope protection has its own envelope protection? ie the autopilot has to be disconnected below certain speeds and heights? Does it have degraded functions alerting the envelope protection is no longer operating?
Does the manufacturer provide an outline training syllabus?
I did the syllabus with help of the vendor by myself. Bank angle protection is not really to worry about as it is easy to understand, but overspeed and underspeed protection really needs training.
