Autopilot induced loss of control

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bkmetz2x205
Airman
Posts: 36
Joined: 27 Jul 2017, 13:24

Autopilot induced loss of control

Post by bkmetz2x205 »

Hi everyone,

I have about 4 hours in the Comanche now. I experienced a problem while using the autopilot. I was cruising at 11000 feet and had low sensing engaged to track a radial from a VOR. The aircraft was trimmed for straight and level. I was near some convective activity as well. I engaged altitude hold on the autopilot, and the aircraft pitched up rather abruptly. It quickly stalled and may have spun. By the time I was able to try to pull out of the resulting dive, I exceeded VNE and suffered an in-flight break-up.

Anybody ever experience anything similar?

Thanks,

-B

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Nick - A2A
A2A Captain
Posts: 13728
Joined: 06 Jun 2014, 13:06
Location: UK

Re: Autopilot induced loss of control

Post by Nick - A2A »

Did you notice if the trim wheel was turning when this upset happened? It sounds a bit like a trim runaway, and although the S-TEC System 30 autopilot doesn't have a pitch trim servo, a few users have reported the trim running apparently of its own accord in the sim.

An FSX/P3D function which is known to cause this is the "Autothrottle enagage (TOGA)" command. Therefore, if you have a joystick button or key assigned to this and it's been activated, that could explain your problem.

In other cases (here's an example), the culprit will be a basic control conflict with the trim commands so this may be worth investigating too.

If you can provide a bit more info on any other software you're using (stuff like FSUIPC and external weather engines) it might provide other clues.

Thanks,
Nick

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guillaume78150
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Location: North Burgundy
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Re: Autopilot induced loss of control

Post by guillaume78150 »

I experienced it once. I managed to recover and could land the A/C. The hangar check reported a trim broken link. My fault, I did not pre-flight...

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Nick - A2A
A2A Captain
Posts: 13728
Joined: 06 Jun 2014, 13:06
Location: UK

Re: Autopilot induced loss of control

Post by Nick - A2A »

Yeah, that's a very good point Guillaume. Definitely worth checking the maintenance hangar (shift 7) before delving into control assignments. :wink:

Thanks
Nick

bkmetz2x205
Airman
Posts: 36
Joined: 27 Jul 2017, 13:24

Re: Autopilot induced loss of control

Post by bkmetz2x205 »

Hi everyone,

Thanks for your help thus far. Sorry it took a few days to get back.

I was not able to tell whether the trim handle moved during the event. I also looked to see if I had the TOGA assigned to any buttons on by controller, and I do not. I can't remember the default key sequence that is assigned, but it requires pressing three keys at once. I am sure that I did not press them.

Concerning a mechanical issue, none were found during preflight. After the crash, the aircraft required multiple repairs, though.

For weather I use Active Sky, but I can't remember which version.

I will report back if the same problem happens again. I was able to use the autopilot successfully on a flight prior to the crash.

-B

shortspecialbus
Staff Sergeant
Posts: 261
Joined: 23 Nov 2012, 09:41
Location: C29

Re: Autopilot induced loss of control

Post by shortspecialbus »

For me this happened with a GoFlight mcp pro that would trigger auto throttle on its own sometimes, which would then lead to runaway trim with the autopilot. I was able to fix it by using pollypot software to disable that switch.

-stefan

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