B737 flight crew detects their aircraft moving backwards after engine shut down at the gate and park...

Narrative:

After pulling into the gate; I received the chocks in signal from the marshaller and released the parking brake. After we completed the 'parking' checklist; I noticed in my peripheral vision outside movement and immediately concluded the aircraft was rolling backwards out of the safety zone. I immediately applied brakes and stopped the aircraft. I opened my window and asked ground personnel to chock the aircraft. They replied; 'it is chocked.' because of the abrupt application of brakes; I was worried passengers may have fallen since the seatbelt sign was off and many were standing in the aisle so I went into the cabin to check on everyone. Flight attendants informed me there were no injuries. I then determined there was no damage to the aircraft and we were then pulled back into the gate. After going down on the ramp to determine what happened; I was shown how slick it was on the ramp; and especially the line paint due to deicing fluid left over from procedures earlier in the day. The aircraft indeed was chocked and simply rolled backward about 12 inches because the ramp was so slick the chock was unable to get the friction required to work properly.

Original NASA ASRS Text

Title: B737 flight crew detects their aircraft moving backwards after engine shut down at the gate and parking brake release and the Captain immediately applies normal brakes. Deicing fluid on the ramp and the painted lead in line combined to allow the nose wheel to push the chock on the slight incline.

Narrative: After pulling into the gate; I received the chocks in signal from the Marshaller and released the parking brake. After we completed the 'Parking' Checklist; I noticed in my peripheral vision outside movement and immediately concluded the aircraft was rolling backwards out of the Safety Zone. I immediately applied brakes and stopped the aircraft. I opened my window and asked Ground personnel to chock the aircraft. They replied; 'It is chocked.' Because of the abrupt application of brakes; I was worried passengers may have fallen since the seatbelt sign was off and many were standing in the aisle so I went into the cabin to check on everyone. Flight attendants informed me there were no injuries. I then determined there was no damage to the aircraft and we were then pulled back into the gate. After going down on the ramp to determine what happened; I was shown how slick it was on the ramp; and especially the line paint due to deicing fluid left over from procedures earlier in the day. The aircraft indeed was chocked and simply rolled backward about 12 inches because the ramp was so slick the chock was unable to get the friction required to work properly.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1067906
Time
Date	201302
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Parked
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 60 Flight Crew Type 12000
Person 2
Function	First Officer
Experience	Flight Crew Last 90 Days 197
Events
Anomaly	Ground Event / Encounter Other / Unknown

B737 flight crew detects their aircraft moving backwards after engine shut down at the gate and parking brake release and the captain immediately applies normal brakes. Deicing fluid on the ramp and the painted lead in line combined to allow the nose wheel to push the chock on the slight incline.