Cabin crew are subjected to exactly the same back ground checks as pilots. At least five years background has to be checked for the issue of an airside pass
The background check for the issue of an airside pass, even for aircrew post 9/11 is very rudimentry and could in no way be called a security clearance in the true sense of the word.
We have a policy of only opening the flt. deck door when the curtain is drawn, fwd toilet unoccupied and additional cc in the forward galley. It works.
Has it ever been tested?. Any determined person, even working alone, could force thier way into the flightdeck when the door is open. The curtain and one extra crew member in the galley will not stop a well trained, violent person who is prepared to use extreme force.
Sky9 is quite correct, and I have said it before, the door needs to be between the galley and the cabin, and another door needs to be on the flightdeck. This would mean there is never an open access to the flightdeck from the cabin. The arrangement that is currently being installed is not a complete solution.
Pre 9/11 the only airline that really took airbourne secrurity seriously was El Al, post 9/11 I suspect that they are still the only ones doing any more than just making it look good. They have a double door.