MD80 CAPT RPTS ACFT ROLLING BACK AT GATE AFTER RECEIVING CHOCKS-IN SIGNAL AND RELEASING BRAKES.

Narrative

ENRTE; THE WX HAD CHANGED AT JFK CAUSING US TO HOLD WHILE THEY TURNED THE ARPT AROUND TO A DIFFERENT RWY. WE BRIEFED THE NEW RWY AND SHOT AN UNEVENTFUL APCH AT DUSK IN THE RAIN. DUE TO THE ARPT BEING TURNED AROUND AND THE RAIN; THERE WAS A LOT OF CONGESTION ON THE TXWYS AND WE HELD OUT FROM THE GATE FOR ALMOST 1.5 HRS. WHEN WE WERE FINALLY CLRED TO THE GATE IT WAS DARK AND RAINING. WE APCHED THE GATE CAUTIOUSLY AS BOTH THE LEAD IN LINES AND THE RED LINES WERE BARELY VISIBLE IN THE DARK AND RAIN. THERE WAS A LOT OF GSE EQUIP ON EITHER SIDE AS WE TAXIED IN. THERE WAS ALSO A LARGE CHOCK JUST TO THE L OF THE YELLOW LINE. WE TAXIED IN; GOT THE STOP SIGNAL FROM THE MARSHALLER; SET THE PARKING BRAKES AND WE COMPLETED THE SHUTDOWN CHKLIST. AS I WAS GETTING OUT OF THE SEAT TO TRY AND SOOTHE SOME VERY IRATE INTL PAX; BOTH THE FO AND I OBSERVED THE MARSHALLER PROVIDE A 'CHOCKS IN' SIGNAL. I REMEMBERED READING ABOUT SETTING THE PARKING BRAKES AT THE GATE; WHICH I DID. NOW; HAVING BEEN GIVEN THE 'CHOCKS IN' SIGNAL; I THOUGHT THAT THE ACFT HAD BEEN CHOCKED AND THAT THEY WANTED ME TO RELEASE THE PARKING BRAKE AS IS THE CASE AT EVERY OTHER STATION. I RELEASED THE BRAKES BASED ON THE MARSHALLER'S SIGNAL AND LEFT MY SEAT. AS I BEGAN TALKING TO THE FIRST CLASS PAX ABOUT INTL CONNECTIONS; I FELT THE ACFT MOVE. I SIMULTANEOUSLY TURNED AROUND AT THE SAME TIME THE FO STOPPED THE ACFT. WE WERE ALL SLIGHTLY JERKED BY THE SUDDEN STOP BUT NONE OF THE PAX WERE KNOCKED DOWN OR HURT. I IMMEDIATELY SET THE BRAKES; OPENED MY WINDOW AND ASKED THE MARSHALLER TO GET HIS SUPVR. THE ACFT HAD ROLLED BACK APPROX 4-5 FT. THERE WAS NO DAMAGE TO THE ACFT AND NO ONE HURT ON THE GND. THE GATE AGENT MOVED THE JETWAY BACK TO THE DOOR (IT HAD YET TO BE POSITIONED ON THE ACFT) AND WE DEPLANED UNEVENTFULLY. APPARENTLY THERE WERE NEVER ANY CHOCKS PUT ON THE ACFT. IN THE DARK AND IN THE RAIN WITH THE AMOUNT OF GSE EQUIP SURROUNDING THE APCH TO THE GATE AND THE BARELY VISIBLE LINES; I DIDN'T SEE THE SIGN INSTRUCTING TO SET BRAKES. AFTER WE DEPLANED; I LEARNED THAT ONE OF THE FLT ATTENDANTS IN THE BACK HAD BUMPED HER FACE ON THE MIRROR WHILE SHE WAS IN THE AFT LAVATORY.