Paul Tomblin writes:

I fly with a Garmin 296 handheld GPS. In my experience, nearly always
just around the same time it says I need to start my descent if I want to
descend at 500fpm to my destination, ATC clears me down to a lower
altitude without being asked.

I have noticed this as well. I suppose if they know the route well,
they know when the descent usually starts.

--
Transpose mxsmanic and gmail to reach me by e-mail.