On iOS safari, one-finger panning doesn’t generate any events until the user stops panning. An onscroll event is only generated when the page stops moving and redrawn.
If all you want is a sticky menu, you can save yourself some headaches by using an existing library. I've had success with iScroll:
http://cubiq.org/iscroll
At the very least, you can take a look at how this works and base your solution around that.
Happy hacking!