Which circuit breakers to collar?

[Marc_B]

On 8/26/2024 at 8:12 AM, Pinecone said:

I collared the Auto Pilot and Pitch trim.

I only collared the AP breaker.  The trim CB only controls the manual electric trim with the GFC500. But doesn’t affect the AP or the trim servo. 

[dkkim73]

Can anyone confirm that there isn't a separate breaker outside the "AP" rocker switch on the Acclaim? (I think this is a GFC 700 question) The electric trim runs, IIUC, through the AP so there aren't two "parallel" ways to actuate it. 

I didn't see anything on the schematic or the panel, but the devil might be in details. Where it usually lives, I think...

[Pinecone]

1 hour ago, Marc_B said:

I only collared the AP breaker.  The trim CB only controls the manual electric trim with the GFC500. But doesn’t affect the AP or the trim servo. 

Ever heard of runaway trim?

 

[Mark942]

IMHO if you collar too many CB's it just makes it confusing. KISS.  I think about what can get me killed quick. Run away trim or run away autopilot. That's the two that have collars.  I don't have speed breaks.

[Marc_B]

11 minutes ago, Pinecone said:

Ever heard of runaway trim?

Absolutely. It’s my understanding that with runaway trim with the GFC500 you must hold the AP disconnect and pull the AP circuit breaker. If you pull the trim breaker the electric trim from the AP still will run. 
if I have a runaway trim there’s no way I’d just pull the trim CB hoping the cause was the manual trim switch alone.  But with pulling the AP breaker the servos are inactivated, because the GFC500 autopilot IS the servos.  So pulling the trim breaker doesn’t depower the trim servo. If I’m understanding this correctly. 

[201Mooniac]

Here is the section from the AFMS on Runaway Trim:

[Marc_B]

@201Mooniac exactly. No mention of a trim breaker as it is just the manual trim switch and doesn’t control the trim servo.

The thread I linked was @PT20J’s description of testing pulling the trim breaker and the AP still ran the trim and the autopilot still functioned as before, controlling/trimming automatically.  The only change was that the manual electric trim switch in the yoke didn’t function, and also important to note that the trim switch wouldn’t disconnect the AP like it usually would in that case.  

[Pinecone]

And what happens if you trim switch malfunctions?  And the trim runs away?????

[jetdriven]

then the autopilot breaker will still kill it. 

[Marc_B]

3 hours ago, Pinecone said:

And what happens if you trim switch malfunctions?

This is an interesting question...as I suspect:

1) if your AP is engaged, a trim switch malfunction would disengage the AP and run the trim, or

2) if your AP off, a trim switch malfunction would run the trim.

BUT...the big take home is that the servo IS the autopilot.  So in all circumstances pulling the AP breaker stops the problem. 

So my default is pull the breaker for the autopilot FIRST while holding the AP disconnect on my yoke.  If you had one of the two events above, I might consider troubleshooting the issue and seeing if I could localize it to the trim switch.  But I suspect that I'd probably just hand fly with the AP breaker pulled until I got on the ground.

[blaine beaven]

I’m doing a panel upgrade this fall, and it has me thinking that I’m going to put three circuit breakers on the far left side of the panel:

Autopilot

Pitch trim

Gear motor

I think these are the most likely ones that need to get pulled in an emergency, so might as well make them easy to find! 

[Pinecone]

Good idea, if you have the room.  Mooney panels fill up quickly