A B737 AFTER PARKING ON A GATE AND RECEIVING THE 'CHOCKS IN' THE CAPT RELEASED THE PARKING BRAKE. ACFT ROLLED BACKWARDS. WHEN BRAKES WERE APPLIED CABIN ATTENDANT AND PAX WERE KNOCKED OVER. NO INJURIES.

Narrative

HAD JUST PARKED THE ACFT AT GATE AND WERE COMPLETING THE PARKING CHKLIST. THE CAPT RELEASED THE PARKING BRAKE AFTER RECEIVING THE 'CHOCKS IN' SIGNAL FROM THE MARSHALLER. WHILE READING THE CHKLIST WE NOTICED THAT THE ACFT SEEMED TO BE MOVING BACKWARDS; BUT WE BOTH INITIALLY ATTRIBUTED THIS PERCEPTION TO THE FACT THAT THE JETWAY WAS MOVING. I THEN CHKED THE GND TO MY R AND IT BECAME CLR THAT WE WERE; IN FACT; ROLLING BACKWARD. I IMMEDIATELY APPLIED THE BRAKES TO STOP THE ACFT AND THE CAPT RESET THE PARKING BRAKE. THE LEAD FLT ATTENDANT (AND I BELIEVE SEVERAL PAX) WERE KNOCKED OVER BY THE STOP; BUT NO ONE RPTED BEING INJURED. THE CAPT OPENED HIS WINDOW TO FIND OUT WHAT HAD HAPPENED AND WE THINK WE HEARD A SNIPPET OF THE CONVERSATION BTWN A RAMP AGENT AND THE RAMP LEAD INDICATING THAT THE AGENT ONLY HAD 1 CHOCK (AND OUR BAD LUCK; HE APPARENTLY PUT IT IN FRONT OF THE WHEEL); INSTEAD OF AT LEAST TWO. IT LOOKED LIKE THE LEAD IMMEDIATELY REALIZED THE FAULT WAS THEIRS; AS HE WENT QUICKLY TO GET THE TOWBAR SINCE WE WERE NO LONGER POSITIONED PROPERLY AT THE JETWAY. THEY TOWED THE ACFT BACK INTO POS AND PROPERLY CHOCKED IT.