The "invincible aircraft" setting is available in the controls. When
 this is on,  press [Ctrl][Tab]. This adds 500 feet to your altitude.
 While in flight or after you die.

 [+][s]   Go into slow mode.
 [+][x]   Turn on your joystick. Now, you can move with your keyboard.
          Here are the keys:

          8 -- hit _ repeatedly _ to go forward
          2 -- hit _ repeatedly _ to go backwards
          4 -- hit _ repeatedly _ to go left
          6 -- hit _ repeatedly _ to go right
          7 -- hit _ repeatedly _ to go up
          1 -- hit _ repeatedly _ to go down