Uncommanded Auto Trim Pitch Down

Mark_Dickens

Member
Joined
May 20, 2012
Messages
86
I've had this intermittent issue where straight and level and with the autopilot engaged, the autotrim will start trimming down with no input from me. This doesn't happen very often but for some reason, it decides to descend. I have to turn off the autopilot and FD to reset it and then it will maintain altitude properly. Turning off the AP without turning off the FD doesn't do anything so the commands are coming from the FD. Just wondering if anyone else has had this happen.
 

DBRV10

Active Member
Joined
Jun 15, 2008
Messages
925
Location
Brisbane, Qld. Australia
Hi Mark,

This is a very known bug and it was in the auto trim from memory. It has been the hardest bug to kill off in my long history of working with Dynon and for that matter my entire industrial automation career. The problem had been impossible to replicate on the work bench, and the diagnostic file only showed the result, and not what caused it.

About a year back, it was found. Lawrence who had been at Dynon since the beginning gave the task to an intern, and between them they managed to replicate the issue on the bench and when they did the problem in the code was staring right at them.

Next was fixing the code and testing. Given the code was fixed and I found this problem many years back, Lawrence gave me a version of software to fly and test. I can report to you the bug is 100% gone and I have now at least 200-250 hours of bug free flying across 4 airframes.

This code is in the next release, which is I am told not far away. That promise has been going all year, but recently I was told that it was now a serious effort to get it released prior to Christmas, and my guess is it will be this month some time.

All the best,
 

kellym

I love flying!
Joined
Sep 29, 2013
Messages
272
Hi Mark,

This is a very known bug and it was in the auto trim from memory. It has been the hardest bug to kill off in my long history of working with Dynon and for that matter my entire industrial automation career. The problem had been impossible to replicate on the work bench, and the diagnostic file only showed the result, and not what caused it.

About a year back, it was found. Lawrence who had been at Dynon since the beginning gave the task to an intern, and between them they managed to replicate the issue on the bench and when they did the problem in the code was staring right at them.

Next was fixing the code and testing. Given the code was fixed and I found this problem many years back, Lawrence gave me a version of software to fly and test. I can report to you the bug is 100% gone and I have now at least 200-250 hours of bug free flying across 4 airframes.

This code is in the next release, which is I am told not far away. That promise has been going all year, but recently I was told that it was now a serious effort to get it released prior to Christmas, and my guess is it will be this month some time.

All the best,
Good to hear a software fix is on the way. There was also a hardware problem with some of the early A/P button panels, that could cause uncommanded pitch trim changes without any command. This caused me to have a completeloss of control that precipitated a stall/spin before I got it under control. Thankfully I had enough altitude to recover. The problem was that if you didn't notice the trim indicator moving, the pitch servo would fight it until it couldn't and give you the airplane with near full up or down trim. Dynon promptly replaced my A/P panel.
 

Mark_Dickens

Member
Joined
May 20, 2012
Messages
86
Hi Mark,

This is a very known bug and it was in the auto trim from memory. It has been the hardest bug to kill off in my long history of working with Dynon and for that matter my entire industrial automation career. The problem had been impossible to replicate on the work bench, and the diagnostic file only showed the result, and not what caused it.

About a year back, it was found. Lawrence who had been at Dynon since the beginning gave the task to an intern, and between them they managed to replicate the issue on the bench and when they did the problem in the code was staring right at them.

Next was fixing the code and testing. Given the code was fixed and I found this problem many years back, Lawrence gave me a version of software to fly and test. I can report to you the bug is 100% gone and I have now at least 200-250 hours of bug free flying across 4 airframes.

This code is in the next release, which is I am told not far away. That promise has been going all year, but recently I was told that it was now a serious effort to get it released prior to Christmas, and my guess is it will be this month some time.

All the best,
This is a relief to know. Fortunately, each time it's happened to me I've been in severe clear conditions. That's great news. I did wonder if it was something I'd done!
 
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