FLC OF AN MDT ACR ACFT LOST CTL OF THE ACFT ON THE RAMP AFTER THE WHEEL CHOCKS WERE PULLED BEFORE STARTING THE ENGS; RESULTING IN THE ACFT ROLLING UNTIL IT HIT A FENCE WHERE IT CAME TO A STOP UNDAMAGED. THERE WERE NO PAX ABOARD!

Narrative

WHILE PREPARING THE ACFT FOR A FERRY FLT FROM TPA TO MIA; PRIOR TO ENG START; THE ACFT ROLLED OFF THE MAIN RAMP INTO A FENCE. UPON MY ARR AT TPA; I MET THE FO AND FLT ATTENDANT AT THE GATE. THE ACFT WAS ON THE REMOTE RAMP (SE CORNER ADJACENT TO GATE). WE ASKED TO HAVE THE ACFT TOWED UP TO THE GATE AND WERE TOLD THAT IT HAD ALREADY BEEN MOVED (TOWED) BY GND PERSONNEL 3 TIMES THAT DAY AND THEY DIDN'T WANT TO MOVE IT AGAIN. WE WALKED OUT TO THE ACFT AND THE FO BEGAN A WALK-AROUND INSPECTION AND THE FA AND I BOARDED THE ACFT. AFTER THE FO GOT ON BOARD; I ASKED HIM IF HE HAD PULLED THE CHOCKS ON HIS WALK-AROUND. HIS REPLY WAS 'NO.' I ASKED HIM IF WE COULD NORMALLY GET SOMEBODY OUT TO THE REMOTE RAMP FOR STARTING. HE WASN'T SURE. I THEN INSTRUCTED HIM TO PULL THE CHOCKS AND WE COULD SIMPLY START ON OUR OWN AND LEAVE. HE DID PULL THE CHOCKS AND REBOARDED. WE WERE DOING OUR 'FLOWS' AND PREPARING THE COCKPIT FOR THE CHKLISTS WHEN THE ACFT STARTED SLOWLY ROLLING BACKWARDS. WE BOTH APPLIED OUR BRAKE PEDALS AND I GRABBED THE PARK BRAKE TO ENSURE IT WAS ENGAGED. THE ACFT ROLLED OFF THE RAMP AND DOWN A GRASSY SLOPE AND INTO A FENCE WHERE IT CAME TO REST. THE TYPE ACFT (DHC-8) HAS AN ACCUMULATOR TO KEEP #2 SYS HYD PRESSURE AVAILABLE TO THE PARKING BRAKE. THIS IS LIMITED TO APPROX 3 APPLICATIONS. EACH TIME THE ACFT HAD BEEN MOVED BY THE GND PERSONNEL THE RELEASING AND RESETTING OF THE PARK BRAKE HAD DEPLETED THE PRESSURE IN THE ACCUMULATOR; SO THERE WAS NO PRESSURE AVAILABLE TO THE PARKING BRAKE. ALSO; IN THAT I HAD NOT TOLD THE FO THAT THIS WAS THE FIRST FLT OF THE DAY FOR THIS ACFT. HE ONLY DID A CURSORY WALK-AROUND AND NOT A FULL PREFLT INSPECTION THAT WOULD HAVE DIRECTED HIS ATTENTION TO AN ACCUMULATOR GAGE IN THE R WHEEL NACELLE. HAD WE GOTTEN TO THE POINT OF RUNNING OUR BEFORE STAR (ORIGINATING) CHKLIST; WE WOULD HAVE SEEN THAT WE WERE BELOW THE MINIMUM PARK BRAKE PRESSURE FOR STARTING (1500 PSI) BUT THE ACFT STARTED ROLLING BEFORE WE HAD A CHANCE.