Getting this back to GA:
It doesn’t disconnect the trim servo. The Check Pitch Trim is just an audio message. You have to deal with it.
The thing is that if this is happening, you will notice something is badly wrong, unless you are asleep.
But in the end this is all “only software” which can fail. The audio connection could also break, although you would notice that earlier 
@Peter some of your forumites operate turbine equipment where compressibility is an issue :) albeit a rarefied minority.
EuroGA from J-3 to transonic :)
The primary problem with pitch trim runaways is controllability. To say it simple: There are two kinds of airplanes and the way a runaway is significant to those differs radically.
1. Airplanes which have sufficient elevator authority to counteract even a full travel trim. Quite a few GA planes are like this, not that many airliners.
2. Airplanes which do NOT have sufficient elevator authority and where trim MUST be moved back into a managable range to stand a chance. Most airliners are like that, some GA planes as well.
The former type actually can withstand a fully blocked up or down trim by counteracting the force manually.
The latter can not and if trim gets stuck in an extreme position or can’t be moved back fast enough, will loose control and crash.
To which of the two an airplane belongs can depend on the elevator design. If the whole stabilizer is trimmed, then it is more likely to be in the 2nd group than if only the elevator itself. Obviously there are also planes which have no stabilizer bbut full moving elevators like the PA28 series and there are such which move the whole empennage like the Mooneys.
Figuring out to which kind your plane belongs can be helpful…
I do not like the concept of aircraft with no manual trim wheel. The motion of the big wheel against your leg is an early indication that the autopilot is doing something.
The CJ4 does not have any manual trim control and the only indication of the trim position is on the MFD. There is a backup electrical pitch trim system. In training the position of the normal pitch trim circuit breaker is an important memory item.
Neil wrote:
I do not like the concept of aircraft with no manual trim wheel
My RV12 has no manual trim. It has an electric trim motor controlled by stick switches or the autopilot. You can limit the trim speed and run-time via the Garmin G3X to hopefully manage the degree of out-of-trim that could occur in a runaway condition.
What if the single motor and its driving electronics fails after it has seriously mis-trimmed the plane?
Is the motor a brush motor, or a 3 phase brushless?
It is like a frozen elevator trim. I got that once, FL140, -14C, after a certain maint company put in some motorcycle lube into the jackscrew. Luckily it thawed at ~3000ft. The KFC225 disconnected. I know a pilot who got this in a CJ, discovered it at FL300, and was lucky there was a passenger present who jammed a suitcase between the yoke and this guy’s (generously proportioned) stomach, and the flight continued thus EGKA-LEMG. Same reason: wrong lube used.
Peter wrote:
What if the single motor and its driving electronics fails after it has seriously mis-trimmed the plane?
In non-autopilot flight, the manual trim speed is set such that if you recognise a runaway within 3 seconds (the same as for a certified aircraft) it will still be within a manageable condition. Not something I want to try! Hopefully the Garmin monitors are adequate to catch an autopilot-induced runaway before it creates too much of a problem.
Peter wrote:
Is the motor a brush motor, or a 3 phase brushless
It’s a simple dc motor. On my RV12 (in common with most RVs) it’s a Ray Allen servo, not a Garmin part.
https://www.boeing.com/commercial/aeromagazine/aero_12/attack_story.html
This has some information on stick shaker and mach.
wigglyamp wrote:
My RV12 has no manual trim. It has an electric trim motor controlled by stick switches or the autopilot.
My club will take delivery of a new Evektor Sportstar RTC any day now. It also has no manual trim, only pushbuttons on the stick. People who have tried say that it is perfectly flyable when maximally out of trim although it of course it will require a constant push or pull.
I don’t recall having seen this on EuroGA:
