Autopilot Master Switch

[Lee A.]

I'm fine tuning my checklist for my Acclaim with GFC700 autopilot.  I have received conflicting advice regarding the AP master switch/breaker.

Some say the engine should be started/stopped with the AP master off.   Some people say they leave it on all the time and never mess with it.

So does having it off somehow protect the AP electronics from dirty power/voltage on the electrical bus?  Maybe there is another reason.

The POH checklist (prior to engine start) says:

1) Circuit Breaker Switches (I think this includes AP) ..... All In.

2)  Rocker switches (does this include AP) ....OFF

 

Since the AP Master is also a circuit breaker rocker switch, you can see the source of the confusion.

I just don't want to blow out an expensive AP!

Thanks,

Lee

 

[N6758N]

Leave all the avionics including the AP master OFF until after engine start, and in reverse, shut them all OFF before shutting the engine down. It's just good practice, even if the chances of a voltage spike, etc.. are low. 

[aggiepilot04]

There's no avionics master on the Acclaim, but I generally leave the alternator and A/P off before startup and turn them off before shutdown.  From what I've been told, the newer avionics are much more tolerant to voltage fluctuations...so this probably isn't helping anything.  For me, it's more out of habit since I had an Avionics master on my J (and it can't really hurt anything).  However, do not switch batteries with the engine/alternator on...you'll find yourself replacing an expensive relay.  Learned that the hard way.

[LANCECASPER]

On an Ovation I had with a KFC225 autopilot and Aspens I had to make sure the Autopilot circuit breaker didn't go in until the Aspen AHRS came up otherwise the Autopilot would go through it's system self-check and fail because it didn't have a good AHRS reading. I made it part of the shutdown checklist to pull the Autopilot Circuit Breaker.