Narrative:

Approximately 5-8 minutes after I received the 'chocks in' signal the aircraft started rolling back! All parking checklists were completed and my first officer was in the cabin as passengers were leaving. I was getting out of my seat when I noticed that the aircraft was moving and my first officer was shouting to set the brakes. I immediately returned to my seat and set the parking brake. The aircraft had rolled back about 2 feet. We immediately stop disembarking passengers and repositioned the jet bridge. Fortunately there were no injuries or aircraft damage. I spoke to the ramp supervisor who informed me that their procedure is to only chock the nose wheel. The main wheels are chocked sometime after the 'chocks in' signal is given to the captain. I found this surprising since I was expecting all wheels to be chocked before I received the 'chocks in' signal.

Google
 

Original NASA ASRS Text

Title: Five minutes after gate arrival and receiving the chocks in signal; the Captain was about to leave the cockpit when he detects the aircraft is moving and quickly sets the brake. After repositioning the jetway the Captain learns that only nose wheel chocks were in place and were apparently not adequate for the slope.

Narrative: Approximately 5-8 minutes after I received the 'chocks in' signal the aircraft started rolling back! All parking checklists were completed and my First Officer was in the cabin as passengers were leaving. I was getting out of my seat when I noticed that the aircraft was moving and my First Officer was shouting to set the brakes. I immediately returned to my seat and set the parking brake. The aircraft had rolled back about 2 feet. We immediately stop disembarking passengers and repositioned the jet bridge. Fortunately there were no injuries or aircraft damage. I spoke to the Ramp Supervisor who informed me that their procedure is to only chock the nose wheel. The main wheels are chocked sometime after the 'chocks in' signal is given to the Captain. I found this surprising since I was expecting all wheels to be chocked before I received the 'chocks in' signal.

Data retrieved from NASA's ASRS site 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.