How do i use the pararchute break with the sr-71?

don't know the techincal term... looks like a parachute coming out the back of the plane...
Umm second to last on on this page http://simviation.com/cgi-bin/perlfect/ ... ll&q=sr-71
Umm second to last on on this page http://simviation.com/cgi-bin/perlfect/ ... ll&q=sr-71