It seems the EX1 Pnuematics system supports multiple APU’s, but there aren’t any key events documented for starting or toggling Bleed air in the individual APU’s. The available Key events don’t seem to support any inputs for an APU index.
Are there any other Key events available to control AU’s if you have more than one?
The K:APU_STARTER event will start all APUs in the fuel and pneumatic system together.
Only the First APU in the fuel system needs to be hooked up to fuel. If more than one exists, all will run with only one getting and burning fuel.
There doesn’t seem to be a way to start just one APU, or shut down just one APU.