emb-145 avionics with APU start
 

on the EMB-145 when starting from a cold and dark cockpit, batteries come on and avionics 1 and/or 2 come on to check volts/temps, then if GPU is avail, can I connect it right then or do I have to shut the avionics back off before connecting the GPU to the elec. system? The reason I ask is because our checklist is saying we have to shut the avionics back off after checking volts and tempsif we are starting APU from batteries ie GPU NOT available. So i was wondering if this is also the case for connecting the GPU as well. thanks

I flip on the batteries and the avionics, then check the GPU voltage, if that is good, I shut the avionics off and connect the GPU and then go from there...

That's how I've been doing it. I don't know if that's how I learned it (I'm assuming so) or just the habit I got into thinking that I will be less likely to possibly damage the avionics.

no no no feel free to engage the GPU after you check the volts etc.. with the avionics on. The only reason you turn off avionics is during APU start due to the load put on the system, not when selecting gpu

Yeah, fire it up. At XJT, we don't ever touch the avionics master switches.

great hey thanks a lot for the replies. I just wanted to check before I jack anything up with the avionics.

I thought it didn't matter if you started the APU with the avionics on because the APU is started by using power from Battery 2. During APU starting, battery 1 is isolated from the load buses. While battery 2 provides power for APU start, battery 1 is used to provide stable electircl power to the equipment that can be adversely affected by voltage transients.

So you can safely turn on the batteries, with the avionic switches engaged, let the APU due the self test, and fire it up.

Well starting the APU with the GPU hooked up you can leave the avionics on but if your only on battery power then you better take those avionics off.

I mean honestly it usually starts anyways becuase i can say i've forgot to hook up the GPU before, but it makes for a much smooth start if you turn the avionics off on battery power. You probably have seen the same i'd figure.

And we all know that this airplane relies on those electrons flowing in the right way

I definitely understand that. The craziest thing I've seen was when the ground personel disconnected the GPU before we even deselected the GPU in the cockpit. The plane freaked out, electrical emergency and contactors clicking and all.

I hated when the ground crews did that, especially when the FMS dumped everything! :mad: Grrr!