Its relatively easy to check the shadowing for problems.
Firstly adjust the seat until you go through the roof and then move it forwards and take a look at your “plane”. You can do this in DX9 or DX10.
Here is the default Beechcraft King
As you can see FSX discards any parts of the aircraft that are not visible from the cockpit. This applies in DX9 or DX10.
Now moving the eye point around the cockpit its fairly easy to find problems. So here I moved to the right .
As you can see this plane has a sunshine roof! The Beechcraft King is probably the worst of the default aircraft.
The default 747 has a few issues – the false colours here are because I wanted to make it easy to spot such problems so I set sunlight as a bright yellow tint and shade as green.
This is in the back of the cockpit looking forwards
And this is in the front footwell.