EDIT: Mirror is working, misunderstood an error message.
@obj
It seems your Raspbian stretch mirror is no longer working:
deb http://flightaware.com/mirror/raspbian/raspbian/ stretch main contrib non-free rpi
It’s not meant to be broken - let me look.
edit: nothing immediately obviously wrong, at a glance the files seem OK and I can fetch the stretch Release file … What’s the error you see?
(FWIW the mirror is actually a complete mirror of the upstream site, there’s no special handling for different distributions etc, we just mirror everything)
Oh i see the issue… wasn’t my script exactly and it didn’t do an apt update so obviously it didn’t work 
Sorry for the noise.