- Start GoogleEarth (I have version 22.214.171.12430 on Gentoo Linux)
- Turn on the "terrain"
- Press ctrl-alt-a
- Choose between an F16 jet fighter, or an SR22 4 seat propeller aeroplane.
- Fly! The mouse works as the usual joystick controller (down=pull up; up=down, just as I like it!)
It may be a bit buggy - if it locks up just restart GoogleEarth, and choose from one of the default starting points.
Of course, I'm not the first to know - Google has fully documented the keyboard shortcuts!