It took me a little time to realise that Fly Mode (menu Navigate -> Fly Mode) is actually activating 'Fly - External Sensor mode', rather than the standard FLY mode (that uses the keyboard).
Fly external sensor does not work with the mouse, and a joystick (or similar) that works with /tmp/inpdev is very non-standard equipment on a Mac. Thus it would be better if Fly Mode on mac OSX evoked the keyboard input method.
Alternatively, if /tmp/inpdev is not available, why not revert to keyboard method rather than revert to Examine mode.
A separate menu items for Fly (extern) and Fly (keyboard) might be most useful.
Keyboard selection to evoke 'Fly - keyboard mode' does work.
p.s. any chance of making a mouse driven fly mode