It's not a net loss...there are new hires every month.
The guys on pprune said the official loss rate is 4% a month, and that's because anyone over 50 is NOT officially leaving...they are retired and don't countin the official loss rate. Pprune guys says the actual loss rate is 11-14% a month. I don't know how many new joiners per month, so I don't know the net loss per month.