Narrative:

Night; VFR; ramp condition was clear of snow; but covered with deice fluid. After blocking at gate while doing post flight flows; I was given the standard 'chocks in' signal from the ramp outside of the forward cockpit window. I remarked to the copilot; 'that was fast.' so I delayed probably 30 seconds before releasing the parking brake. The first officer and I ran the parking checklist and began to gather our belongings and throw away trash from our seats. Probably 3-5 minutes after we blocked in; as I looked down to my left placing my ipad in my flight bag on my left; I noticed some movement on the jetway. I saw two passengers standing there looking a little bewildered; and I realized the aircraft was moving backward. I quickly applied the brakes; then set the parking brake. I would estimate we moved 2 feet; based on where the jetway canopy was now located on my window. Within a minute or two; a ramper came up the jetway stairs and asked what happened. I told him the brakes were off; but now set and it appeared to me we moved backward. No one was injured on the jetway. Deplaning was stopped; and I told him I had received the 'chocks in' signal from a different ramper. He and the agent determined repositioning the jetway was the best solution to get people off quickly. Door 1L was not affected by the movement and the ramper assured me no one or equipment on the ramp was injured or damaged. The agent repositioned the jetway and deplaning was completed. The ramper told me the chocks must have slid; but assured me they were in place. I left the aircraft with brake set.

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Original NASA ASRS Text

Title: B737 Captain reported that after being given the 'chocks in' signal the aircraft started rolling backwards.

Narrative: Night; VFR; ramp condition was clear of snow; but covered with deice fluid. After blocking at gate while doing post flight flows; I was given the standard 'chocks in' signal from the ramp outside of the forward cockpit window. I remarked to the copilot; 'that was fast.' So I delayed probably 30 seconds before releasing the parking brake. The First Officer and I ran the parking checklist and began to gather our belongings and throw away trash from our seats. Probably 3-5 minutes after we blocked in; as I looked down to my left placing my iPad in my flight bag on my left; I noticed some movement on the jetway. I saw two passengers standing there looking a little bewildered; and I realized the aircraft was moving backward. I quickly applied the brakes; then set the parking brake. I would estimate we moved 2 feet; based on where the jetway canopy was now located on my window. Within a minute or two; a ramper came up the jetway stairs and asked what happened. I told him the brakes were off; but now set and it appeared to me we moved backward. No one was injured on the jetway. Deplaning was stopped; and I told him I had received the 'chocks in' signal from a different ramper. He and the agent determined repositioning the jetway was the best solution to get people off quickly. Door 1L was not affected by the movement and the ramper assured me no one or equipment on the ramp was injured or damaged. The agent repositioned the jetway and deplaning was completed. The ramper told me the chocks must have slid; but assured me they were in place. I left the aircraft with brake set.

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.