Okay, so I know I shouldn't be playing around in flight with features I haven't experimented with before while on the ground. Nevertheless, I tried "Screen Brightness>Darken Screen" today in flight. During the day.
Somehow I managed to darken my screen to zero. (Or near zero.) Big mistake.
(Question: Why does iFly allow the screen to go to zero in the first place? Shouldn't 10% be the lowest? Or some User preset lower limit?)
Is there an on-screen gesture or Android button combination to get back to a bright screen?
As it was, I tapped frantically at where I remembered the "Brighten" button being. Fortunately, that worked.
Now that I'm home, I see that, fortunately, these settings don't persist across reboots. So in a real pinch, I could reboot my tablet in flight to get the screen back to normal.