Question re Autopilot Circuit Breaker

eetrojan

eetrojan

Pattern Altitude
Joined
Jan 19, 2012
Messages
1,531
Location
Orange County, CA
Display Name
Display name:
eetrojan
The photo below shows the autopilot circuit breaker ("CB") in one of the Cessna 172's I'm now training in. Isn't this CB supposed to be "pullable?"

To my untrained eye, the autopilot CB only looks like it's designed to be pushed back in if it pops opens, but not manually pulled out. Compare it with the GPS CB to the right,

Am I missing something?

Auto_PIlot_Circuit_Breaker.jpg
 
Our rule... For the last several places I have worked:

Reset a breaker ONLY if it's essential to continue flight, and than only once. Certain breakers (taught in training) are never to be reset.
 
Thanks. To clarify why I'm asking, I'm wondering about being able to PULL the CB in order to disable the autopilot, not reset it by pushing it back in.
 
There are some flush breakers that pop after you push and hold them for a moment.
 
brien23 said:
Circuit Breaker and Fuse are protection for wiring not a on off switch.
Click to expand...

WRONG. Not for an autopilot.

If it misbehaves, you want this to be able to completely disable it in flight. Microswitches can fail, and a stuck on autopilot is a landing hazard.

Having had a GFC700 glitch and command full nose down trim, the circuit breaker is a nice alternative to turning the master off.

To the OP, you're not missing something. It may or may not be required by reg, but you sure as heck want the capability. And that CB looks like hell. It's a KAP140, right?
 
Last edited:
Looks like standard crap CBs to me. They are only about $20 each brand new. Convert it to a pullable one via minor alteration.


I have NEVER seen the flush type in a transport category airplane. Why they found their way into GA stuff who knows.
 
Off topic, but... you have both a FlightStream and a GDL88 in that C172? Nicely equipped!
 
Submitted for your consideration (cue the Twilight Zone theme):
- recently when getting my GDL88 installed, I asked the avionics shop to change the AP CB to a pullable one.
- when picking up the plane noted the CB hadn't been changed
- when inquired was told this wasn't an approved modification on an AA5!

- I will not be returning to that avionics shop.
 
wrbix said:
Submitted for your consideration (cue the Twilight Zone theme):
- recently when getting my GDL88 installed, I asked the avionics shop to change the AP CB to a pullable one.
- when picking up the plane noted the CB hadn't been changed
- when inquired was told this wasn't an approved modification on an AA5!

- I will not be returning to that avionics shop.
Click to expand...

I wouldn't either. Circuit breakers on a plain old CAR3/Part 23 isn't brain surgery.

If they can't get you a pullable one with a simple log entry (no other FAA approval needed) after reading this.... http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23-27.pdf

Or altering it via AC43.13...
 
I have pullable circuit breakers but I also have both autopilot and trim disconnect switches on the panel in addition to the big red button and the doubly redundant trim switch on the yoke.
 
Thanks all! Here a few responses, some additional info from the POH, and another dumb question.

brien23 said:
Circuit Breaker and Fuse are protection for wiring not a on off switch.
Click to expand...

MAKG1 said:
WRONG. Not for an autopilot.

If it misbehaves, you want this to be able to completely disable it in flight. Microswitches can fail, and a stuck on autopilot is a landing hazard.

Having had a GFC700 glitch and command full nose down trim, the circuit breaker is a nice alternative to turning the master off.

To the OP, you're not missing something. It may or may not be required by reg, but you sure as heck want the capability. And that CB looks like hell. It's a KAP140, right?
Click to expand...

It is a KAP 140, the single axis version which evidently means roll (wing leveler) or heading, but not altitude.

In the other thread about the pilot that lost control of his aircraft while fighting a malfunctioning autopilot, pulling the circuit breaker was one of the suggested ways of disabling it.

I’m becoming familiar with a new plane, for me, and figured I should fully understand it.

In the photo above, the black circuit breakers look "pullable" and the white ones look "resettable."

I just looked, and the 172S POH specifically says that you should be able to “pull out” the circuit breaker. It doesn’t look to me like the autopilot's white circuit breaker is very "pullable":

Auto_Pilot_POH_01.jpg


I’m still confused about the autopilot fuse that I’m seeing because the electrical system description also says that the fuses should be “pullable” and not merely resettable:

Auto_Pilot_POH_02.jpg


I don’t think that it’s the case, but maybe the “ring” normally used for pulling has broken off?


TangoWhiskey said:
Off topic, but... you have both a FlightStream and a GDL88 in that C172? Nicely equipped!
Click to expand...

Thanks for that observation! I flew this plane for the first time about a week ago and was surprised to be getting traffic alerts on the Garmin 530. Now I know why.

It sounds like the Flight Stream 210 will wirelessly link the Garmin 530 with my iPad, using Foreflight (I already have a Pro+SynVis subscription) or Garmin Pilot (just downloaded a 30-day trial). Supposedly you can see weather, see traffic, power the synthetic vision, and transfer flight plans back and forth. Can’t wait to try it!

warthog1984 said:
Look on the backside of the yoke. There's a separate (small) pullable CB for the AP.
Click to expand...

Will do. Thank you.

Is this button on the left yoke the “AP TRIM DISC” button mentioned above? The push-to-talk (PTT) button is on the back side of the same handle.

Auto_Pilot_Trim_Disc_Button.jpg
 
Last edited:
Side bar:

You can certainly buy colored collars for pullable circuit breakers to make it easy to locate & identify marked ones quickly.
 
MAKG1 said:
WRONG. Not for an autopilot.
Click to expand...
He's not wrong.
The reasons he stated are exactly the purpose of CBs and fuses from an electrical design standpoint.

But yes, for an Auto Pilot CB you should have a means of pulling the CB.
 
Fearless Tower said:
He's not wrong.
The reasons he stated are exactly the purpose of CBs and fuses from an electrical design standpoint.

But yes, for an Auto Pilot CB you should have a means of pulling the CB.
Click to expand...

I think most autopilots make the disconnect button on the yoke the final authority. That's why they get written up as unairworthy when those buttons don't work. Also, why a $5 parts costs MEGA $$$.

I'd be willing to bet pretty much all flight manual supplements for autopilots require function test of the disconnect system during preflight.
 
register@teamandras.com said:
It is a KAP 140, the single axis version which evidently means roll (wing leveler) or heading, but not altitude.

...

I just looked, and the 172S POH specifically says that you should be able to “pull out” the circuit breaker. It doesn’t look to me like the autopilot's white circuit breaker is very "pullable":
Click to expand...

Careful. That is not the POH for your aircraft. You have a very different autopilot, and its checklists may be different. Though I certainly would pull the CB if I got a PTRM annunciation. From previous experience, KAP140s just don't do anything (at least sometimes) with that annunciation. But if yours is single axis, it can't possibly get that annunciation.

I wasn't aware that a single axis KAP140 existed, especially in a G1000 aircraft.

register@teamandras.com said:
Is this button on the left yoke the “AP TRIM DISC” button mentioned above? The push-to-talk (PTT) button is on the back side of the same handle.
Click to expand...

I hope not. He's talking about a circuit breaker. That's just a momentary disconnect. On a G1000, it will set off the disconnect alarm (GAWD I hate that noise).
 
bnt83 said:
I'd be willing to bet pretty much all flight manual supplements for autopilots require function test of the disconnect system during preflight.
Click to expand...
Yes and some (like the Florida accident airplane) even have placard on the instrument panel telling you to test the system before flight.
 
MAKG1 said:
Careful. That is not the POH for your aircraft. You have a very different autopilot, and its checklists may be different. Though I certainly would pull the CB if I got a PTRM annunciation. From previous experience, KAP140s just don't do anything (at least sometimes) with that annunciation. But if yours is single axis, it can't possibly get that annunciation.

I wasn't aware that a single axis KAP140 existed, especially in a G1000 aircraft.
Click to expand...

Doh! Thanks Mak. That's what I get for using a generic POH. Yeah, it doesn't have a G1000, just a 530.

I'm going to rent this plane for a sunset flight over the next few days. That way I'll have access to the plane for a few hours after closing and then I can leisurely scan in the real POH, supplements, and other on-board manuals.

I wish that GA's rental fleet made the real serial-numbered stuff routinely available by PDF. Maybe they're concerned about the liability of the PDFs falling out of sync with the updates and upgrades? Edit: or copyright issues?
 
Last edited:
The breaker in the photo looks very much like the Tyco brand W58 circuit breaker. Their literature states that that breaker is "push-to-reset" ONLY. And, "it cannot be manually tripped."

I'd ask your CFI, and or the FBO manager about this. There should be 3 ways to disable the installed autopilot 1) the on-off switch, 2) the A/P trim Disc switch on the yoke and, 3) a pullable circuit breaker.
 
I think Cessna went after operators that had done that, for copyright. A few years ago, it was common to find online versions, and you may find a bootleg one flying around. IMO, a lot has been lost, and Cessna should be ashamed of themselves for the safety hassles they created.

FYI "Nav III" = G1000. GFC700 is the later autopilot, and is quite different from the KAP140, much more integrated with the flight deck. Also, it's wildly complex with flight-planned VNAV modes and a gazillion obscure rules about when it transitions and when it doesn't.
 
Yes, my autopilot makes a raucous beeping when it disconnects (either by the red button or by moving the trim switch or if it decides it's hit some limit of operation). Wakes the pilot up that he needs to be flying.
 
wilkersk said:
The breaker in the photo looks very much like the Tyco brand W58 circuit breaker. Their literature states that that breaker is "push-to-reset" ONLY. And, "it cannot be manually tripped."
Click to expand...

Yep I agree with that. My airplane has one or two of those left but the majority are the ones that I can pull.

Also of note, the autopilot circuit breaker in that picture looks like it's already tripped. Normally they sit flush, when they trip they pop out.
 
fiveoboy01 said:
...the autopilot circuit breaker in that picture looks like it's already tripped. Normally they sit flush, when they trip they pop out.
Click to expand...

Hmmm. You may well be right. I didn't even try to turn the AP on in my first and, thus far, only flight in this plane.
 
brien23 said:
Circuit Breaker and Fuse are protection for wiring not a on off switch.
Click to expand...

Not arguing, but in Flight Design CT's a breaker is used as a master.

Not saying it's a good design, but it is one which has at least one application.

I think you can see it on the lower right in the left image here:

1112p_flight_design_6.jpg
 
Last edited:
Fearless Tower said:
He's not wrong.
The reasons he stated are exactly the purpose of CBs and fuses from an electrical design standpoint.

But yes, for an Auto Pilot CB you should have a means of pulling the CB.
Click to expand...

Well, he's not right either, it depends on the design. Many CBs are indeed meant to serve the function of an on/off switch. I believe you have a few of hem in your Baron.
 
Henning said:
Well, he's not right either, it depends on the design. Many CBs are indeed meant to serve the function of an on/off switch. I believe you have a few of hem in your Baron.
Click to expand...

Regardless of whether or not it has that feature, that is NOT the primary purpose of a CB.
 
Fearless Tower said:
Regardless of whether or not it has that feature, that is NOT the primary purpose of a CB.
Click to expand...

The primary purpose of a circuit breaker is to open, or break, a circuit. Whether the switching is thermal or mechanical isn't really a big deal to it. If the unit is designed with both capabilities, it can be used either way. What type any given aircraft will use is a matter of overall design ergonomics.

To say that the thermal circuit breaker is not meant to be the primary mechanical circuit breaker, is not a correct statement as it discounts many applications where it is, like your own panel.

How many shops and hangars to you walk into and turn every thing on and off at the breaker panel?:dunno: Most of the ones I ever worked in.
 
Henning said:
How many shops and hangars to you walk into and turn every thing on and off at the breaker panel?:dunno: Most of the ones I ever worked in.
Click to expand...
Just because you use it a certain way doesn't mean anything as far as a circuit breaker's PRIMARY purpose in an electrical system. I would sincerely hope that someone who captains vessels would understand that....but then I know you like to argue.
 
MAKG1 said:
Having had a GFC700 glitch and command full nose down trim, the circuit breaker is a nice alternative to turning the master off.
Click to expand...

Sure you didn't forget the AP was on, fight with the GFC700 thus forcing it to trim? ;) Having trouble believing the GFC700 "glitch" theory...
 
Fearless Tower said:
Just because you use it a certain way doesn't mean anything as far as a circuit breaker's PRIMARY purpose in an electrical system. I would sincerely hope that someone who captains vessels would understand that....but then I know you like to argue.
Click to expand...

Again, the PRIMARY purpose is what ever the designer who put it there intend it to be, just like in your Baron. If the primary reason is thermal protectetion, so be it. However as is the case with your landing light switch/CB, the PRIMARY function is to turn the light on and off, and that switch has a thermal shunt that serves an ANCILLARY function of thermal protection, combined in the same CB housing.

I'm just trying to point out not to get hung up pigeonholing the definition because it does not hold true always.
 
Last edited:
Mechanics on the line or in the hangar will pull CBs for three primary reasons.

1. To remove power on that individual circuit for component R&R or other maintenance without removing power from the entire aircraft. That allows other work which requires power to continue.

2. Due to a step in an operational check that calls for the CB to be pulled to simulate a failure or other event.

3. To apply a MEL.

They do not however use the CB as an on/off switch to operate the system.

I do agree however that having the ones that you can easily open by pulling are easier to deactivate a system if needed. They are also much easier to place a collar on if you want to leave a system deactivated.

I will also agree that having one is a good idea for certain systems that if the switch or switches fails in flight would result in a dangerous situation. Autopilots and electric trim fall into this category. They also come in handy for the landing gear so that the CFI can pull it when you are not looking to simulate a gear failure.

At the end of the day though their primary purpose is for circuit protection.
 
Again remember, if it's a flush button type, many of them are still 'pop able' (and function tested by) pushing them in and holding them for a moment until they pop.
 
I am with Henning on this. The PRIMARY function of the device is whatever the designer intended it to be. Some breakers were designed to be switches also and some switches were designed to also be breakers.

It's not really worth arguing about. But then again . . .
 
Why are y’all arguing about the "primary purpose" of a circuit breaker?

Would I violate some sort of "prime directive" if I pulled a pullable breaker to resolve an emergency situation?:goofy:
 
You must log in or register to reply here.
Back
Top