Know Your Circuit Breakers

[Max Clark]

Didn't want to hijack Don's thread (below), but it triggered an experience I had that's worth sharing as a cautionary tale.

In my case I was flying a rental C182R with Dual G5s and a GFC500 autopilot (as an aside, a really nice setup to fly). I received a clearance to climb, dialed in the altitude select, pressed IAS and dialed back the speed to cruise climb. The plane pitched up... 7°, 10°, 12°, 15° and kept on going. Before crossing 15° I was already putting forward pressure on the yoke and pressing the AP disconnect button. AP disconnect was not disconnecting, and the AP was fighting me to continue to pitch up. I'm a fairly big guy and with two hands on the yoke it was taking everything I had to keep the pitch down. It took me longer than I'd like to admit to remember to pull the AP and Servo circuit breakers. Except I didn't know exactly which ones they were, and my attention was focused on my fight. I started pulling everything in the general area until the yoke pressure left, got my wits about me, and then figured out which CBs could be put back in.

Maintenance didn't find an issue, and to my knowledge it didn't happen again to another person. I have no idea why I was the lucky one.

As part of my preflight now I make it a point to touch the AP and Servo CBs while I call them out verbally (yes out loud).

 

 

[201Mooniac]

Max, I always collar with AP breakers with a red collar so they are easy to find.  I've never had to but I expect I could even get a right seat passenger to just pull the red breakers if it took both of my hands on the yoke.  I think your callouts would be especially helpful in flying another plane than my own, I'll need to remember that.

[N201MKTurbo]

If you are getting a trim runaway, you can always turn off the master until you sort out the circuit breakers. I know it can be a pain because you loose all the avionics and h@ve to set them up again.

[PT20J]

If the autopilot is engaged and you push on the yoke it will normally trim against your input so when you disconnect the autopilot, the airplane will not be in trim.

On autopilots I have flown, the yoke disconnect switch should be held down to remove power from the servos until you get the autopilot off.

It's a good idea to review the autopilot emergency procedures in the AFMS periodically because autopilot failures, while rare, can easily lead to loss of control.

[Mooney in Oz]

16 hours ago, PT20J said:

It's a good idea to review the autopilot emergency procedures in the AFMS periodically because autopilot failures, while rare, can easily lead to loss of control.

This ^^^^^

IMHO the AFMS has much more important info than the PG and is essential reading.

A runaway trim is the first and only item in the Emergency Procedures with the first few lines in bold print indicating the lines that should be committed to memory and the sequence to follow.

It also contains other useful and need to know information, such as limitations.

I also have my Autopilot CB red collared. Don’t get it confused with the Trim CB. A Pitch Trim failure is a separate, non-memory item that is also covered.

[skykrawler]

Seems unlikely the autopilot did not disconnect. 

It is more likely the autopilot miss-trimmed nose up (wasn't there an AD?) such that when disconnected the forces were high.  

 

 

[GeeBee]

Then there are those really crappy CBs that are flush and cannot be pulled like Cessna used for so many years

[201er]

20 hours ago, N201MKTurbo said:

If you are getting a trim runaway, you can always turn off the master until you sort out the circuit breakers. I know it can be a pain because you loose all the avionics and h@ve to set them up again.

The master switch is easy to reach and one of the easiest "feel" items because we use it before and after every flight (unlike breakers and other buttons). There are mechanical backup instruments. Just disconnect all power, eliminate all problems, get it flying, and then work on diagnosing.

[Max Clark]

20 hours ago, PT20J said:

It's a good idea to review the autopilot emergency procedures in the AFMS periodically because autopilot failures, while rare, can easily lead to loss of control.

Really good point. It's been so long I couldn't tell you if I was holding or pressing the disconnect button. I probably couldn't have told you immediately after the flight on the ground either.

Reading through the GFC Emergency Procedures I'll definitely be press and hold in the future.

[PT20J]

The TRIM CB will kill the power to the trim servo on the King autopilots. But, on the GFC 500, it will only render the manual electric trim inoperative; the autopilot can still actuate the trim servo. That’s why you need to pull the autopilot CB and not the TRIM CB with runaway trim on the GFC 500

One good thing about Garmin ESP design is that it only commands the pitch and roll servos. It doesn’t use the trim servo. So, it can’t get you dangerously out of trim like the infamous Boeing MCAS.

 

[MikeOH]

Reading all of this, I'm actually pretty happy that I do NOT have electric trim with my STEC-30.  Pretty well impossible for my AP to try and kill me with trim

[Flyler]

Century 41 with electric trim in my 201. Pulling the AP circuit breaker does not disable the electric trim.  There is a separate switch near the throttle knob to turn it on/off.

[IvanP]

I have put a yellow collar on my A/P CB. Also, my setup has a switch right in front of me that disconnects the trim servo. Makes handling runaway trim a bit easier (fortunately I have not had it happen yet on this plane).

[Max Clark]

On 12/23/2025 at 9:29 AM, 201Mooniac said:

Max, I always collar with AP breakers with a red collar so they are easy to find.  I've never had to but I expect I could even get a right seat passenger to just pull the red breakers if it took both of my hands on the yoke.  I think your callouts would be especially helpful in flying another plan than my own, I'll need to remember that.

In addition to the red for ap/trim any others that you collar?

[IvanP]

Gear actuator is also collared in my plane - in case I need to do manual extension, the C/B needs to be pulled.

[201Mooniac]

On 12/24/2025 at 7:22 PM, Max Clark said:

In addition to the red for ap/trim any others that you collar?

I have red collars on AP & trim, yellow on gear actuator in case I need a manual extension. 

[Thedude]

6 hours ago, 201Mooniac said:

I have red collars on AP & trim, yellow on gear actuator in case I need a manual extension. 

That's funny that's my exact set up too, plus green on the pfd and radio 1

[Pinecone]

On 12/23/2025 at 12:29 PM, 201Mooniac said:

Max, I always collar with AP breakers with a red collar so they are easy to find. 

Same here