@casperchen0211
The King Air is one of the most complex aircraft one can fly single pilot, but it is not that hard when you understand the systems and why they exist. As I had similar questions I can provide you with answers I found... As I am no King Air pilot in real life there may be errors.
Enviromental - Bleed Air Switches
The Bleed Air System has 3 positions because the KingAir uses bleed air not only for pressurization. It is using air also for air conditioning (Temperature inside the cabin) and Instruments (some analog instruments use a vacuum). With this switch in the Envir Off position for example, you switch off the cabin air conditioning for startup because if the engine starts burning during startup you dont want smoke inside the cabin.
With the switch all the way down you switch off air for air conditioning AND air for instruments.
Anti Icing - Engine Anti Ice
The engine anti ice on the King Air works a little different then on other aircraft. As far as I know the main air inlet on the engine is always heated with warm engine bleed air, you can not switch this off or on.
The engine anti ice switches are activating a system called "Inertial Seperator" - You can imagine a "plate" which is moved into the air stream which enters the engine from the front. This plate is positioned in a way that it deflects debris (like parts of ice) away from the inner workings of the engine. It is normaly also set to on when on ground outside of icing conditions because it also deflects foreign objects like stones or other debris from the ground. Because this plate limits the air entering the engine you can also see a little loss or gain of Torque when turn this system on or off in flight.
The ACTUATORS STBY switch just activates the second set of motors which move this plate. This is in case the main motors stop working.
Anti Icing - General, Prop, Wing
All in all, if the static air temp is below 10°C and there are signs of water in the air (Rain,Snow,Clouds,Mist....) you should turn on anti icing equipment.
BUT: On the King Air this only counts for the Prop Heat in my opinion because the Surface De-Ice is already giving you a hint of what it does - it DE-ices the wings.
Normally you turn this system on if you can see ice build up on the leading edge of the wings (for the night there are ICE LIGHTS which illuminate the wings). I also have read that you should wait for enough ice to build up on the wings because the de-ice effect works better in this case (I dont think this is modeled in the sim).
This system is pretty simple. The leading edges of the wings are covered with a rubber material which inflates a bit when you turn it on. This brakes any ice that has built up which flys off with the airstream over the wings.
Anti Icing - Other Switches or "The hot 5"
All the other switches are systems which you need for every flight - normally turned on just before takeoff or taxi. These warm up vents and probes which are essential for every flight. They are called the "Hot 5" because these are 5 switches you always turn on. These are: 2x Fuel Vents, 2x Pitot Heat and the heating for the stall warning sensor.
For the windshield anti icing you can use the same margins as for the prop heat I think - OAT below 10°C and water in the air. Or if you see ice build up on the windshield. I always switch it to normal when I switch on the Hot 5.
Prop Sync
I dont know HOW this system actually works (there is some engineering magic behind it) but it syncronizes something on the propellers so that they are quiter for pilots and passengers. This has something to do with sound waves and how they wander thru the air. I always thought this has something to do with the actual prop setting, but it exists to make the cabin a quieter place - because two Turboprops are already loud enough.
I turn it on in climb and turn it off before approach.
I hope this helps! Have Fun!
