Down Pool Member via iRule

I'm trying to write what I think is a basic iRule:

when HTTP_RESPONSE { 
 if { [HTTP::status] equals 503 }{ 
 log local0. "[IP::server_addr] is currently causing 'Server Unavailable'" 
 Down the member that is serving 503's 
 } 
 }

I'm not quite sure how to down a member with an iRule or if it's even possible. I've searched a bit, but I haven't found anything. Anyone do something like this or know if / how it's possible?

Thanks!

P.S. This is 9.x