A320 FLT CREW HAS FAILURE OF THE COCKPIT DOOR LOCKING SYSTEM AND ELECTS TO DIVERT TO ZZZ1.

Narrative

ABOUT 1 1/2 HRS INTO THE FLT; FLT DECK DOOR WAS OPENED AND THEN COULD NOT BE CLOSED. THIS PROB OCCURS ON THE A320 SERIES AND IS NOT UNCOMMON. BECAUSE THERE IS NO SECONDARY LOCK; LATCH; BAR; ETC; DESIGNED FOR THE DOOR; IF THE PRIMARY FAILS; THERE IS NO BACKUP TO SECURE THE DOOR. BECAUSE OF THIS; AS CAPT; I CHOSE TO USE CAPT'S EMERGENCY AUTHORITY TO DIVERT FROM OUR ORIGINAL DEST AND LAND AT ZZZ1. THIS ALSO ENTAILED AN OVERWEIGHT LNDG AND PLACING A FEDERAL LEO IN THE JUMPSEAT TO GUARD AGAINST INTRUSION. WITH THE DIVERSION FROM ATC; WE PROCEEDED TO ZZZ1 AND LANDED. PAX WERE DEPLANED AND THE ACFT WAS PLACED ON MAINT FERRY TO REPAIR THE DOOR. THERE IS AN URGENT NEED FOR THE DESIGN OF THE DOOR TO BE MODIFIED; AND CLR CONCISE DIRECTION FROM THE CARRIER AND THE FAA ON WHAT COURSE OF ACTION TO TAKE IN A SIMILAR EVENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE DOOR SYSTEM IN THIS ACR IS AN ELECTRICALLY CTLED SYSTEM THAT IS ACTUATED BY THE COCKPIT DOOR SWITCH LOCATED ON THE CTR CONSOLE. THE DOOR HAS A SERIES OF CAMS THAT SLIDE LOCKING PINS INTO THE DOOR FRAME TO SECURE THE DOOR. THE DOOR IS TIGHTLY FITTED WITHIN THE FRAME AND WHEN THE ACFT BECOMES AIRBORNE THE FLEXING OF THE AIRFRAME FROM AERODYNAMIC PRESSURES; CENTER TANK FUEL LOADS; CABIN PRESSURIZATION AND TEMPERATURE CHANGES CAUSES THE DOOR TO MISALIGN AND THE FLT CREW IS UNABLE TO CLOSE THE DOOR. THE RPTR INDICATED THAT THIS IS AN ONGOING PROB WITHIN THE ACR'S A320 SERIES FLEET. IF THE DOOR IS CLOSED AND IT IS MISALIGNED DUE TO THE ABOVE REASONS THE LOCKING PINS WILL NOT SLIDE INTO THE LOCKING HOLES. THERE IS NO BACK-UP SYSTEM SUCH AS A MANUAL SLIDING BAR OR MANUAL LOCKING PIN.