When a commercial airline arrives at the gate, and before the flight deck crew leaves the flight deck, what systems are left "on" and what systems are turned "off" (along with the engines of course)? I read from somewhere that the flight deck is not completely "cold and dark" when the plane is at the gate waiting for the outbound crew to board. Is this true?

 

ERA

I'd think most of your electrical systems would be left on, probably pneumatics as well. When you think about it, the IRS generally takes ten minutes to align, and on some flights, you have some pretty short turns. It would be highly illogical to turn everything off only to have to turn everything back on a few minutes later. Now if it was the last flight of the day and the next flight isn't until eight hours later, then yes, you'd likely turn everything off.

It really depends on a number of factors - facilities at the airfield, ambient temperature at the airfield and of course the type of aircraft.

 

You most definitely don't go cold and dark if the aircraft is going to depart again.  As a general rule (assuming ground air/elec is available)

 

Depressurize the hydraulics, shut down the APU if not needed (sometimes it is better to stay on APU in hot country's)  Shut off the fuel pumps, emergency lighting systems, weather radar.   IRS/ADIRU can be fast aligned on a quick turnaround.

 

Even if it is the last flight of the day you will have ground crew/cleaners & engineers working on the aircraft. It is very rare that you have to shut down everything yourself.