Narrative:

All aircraft slides were confirmed 'disarmed' per standard operation procedures (SOP) at post flight; after block-in and engine shutdown in ZZZ. Approximately 20-minutes later; the first officer performed a post-flight walk around with no discrepancies noted. A few minutes later I noticed several of the ground crew were in the aft galley and aft few rows of the aircraft; instead of spread out; cleaning and doing their security search. The shift manager approached me in the cockpit seeming very upset. She said something about the slide and was surprised I had not been told the door-4R (right) slide had been deployed. During this whole time my entire flight crew was in the front of the aircraft (first class or cockpit) so none of us witnessed the event. When I went back to door-4R; I found the door secured in the open position; the slide completely deployed; and the arm handle in the 'unarmed' position. The slide was removed by maintenance and moved to the aft cargo compartment. The flight was canceled; we received a new release and ferry permit and ferried the aircraft to ZZZ1 with only the crew on board. It is unclear to me; since none of my crew witnessed the event; why it occurred. It could have been human error or some type of mechanical failure with the door and/or slide mechanism. I will probably never be told.

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Original NASA ASRS Text

Title: An A320 Captain reports after all aircraft slides were confirmed 'Dis-Armed' after block-in and engine shutdown; a Shift Manager informed him the Door-4Right slide had deployed. Captain notes slide was fully deployed and the Arm handle in the 'Unarmed' position. Cause unknown. Flight was canceled and aircraft ferried for slide replacement.

Narrative: All aircraft slides were confirmed 'Disarmed' per Standard Operation Procedures (SOP) at post flight; after block-in and engine shutdown in ZZZ. Approximately 20-minutes later; the First Officer performed a post-flight walk around with no discrepancies noted. A few minutes later I noticed several of the Ground crew were in the aft galley and aft few rows of the aircraft; instead of spread out; cleaning and doing their security search. The Shift Manager approached me in the cockpit seeming very upset. She said something about the slide and was surprised I had not been told the Door-4R (Right) slide had been deployed. During this whole time my entire flight crew was in the front of the aircraft (first class or cockpit) so none of us witnessed the event. When I went back to Door-4R; I found the door secured in the open position; the slide completely deployed; and the Arm handle in the 'Unarmed' position. The slide was removed by Maintenance and moved to the aft cargo compartment. The flight was canceled; we received a new Release and Ferry Permit and ferried the aircraft to ZZZ1 with only the crew on board. It is unclear to me; since none of my crew witnessed the event; why it occurred. It could have been human error or some type of mechanical failure with the door and/or slide mechanism. I will probably never be told.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.