CONFRONTED WITH AN ABNORMAL ENG START PROC FOR WHICH THEIR RECENT COMPANY OPS MANUAL DID NOT PROVIDE A CHKLIST; MD88 FLT CREW FAILS TO ENSURE PARKING BRAKE SET BEFORE ENG START AND ACFT ROLLS FORWARD DAMAGING THE TOW BAR.

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THE ACFT APU WAS INOP FOR DISPATCH SO DECISION WAS MADE TO START BOTH ENGS AT THE GATE. I ASKED THE FO IF HE WOULD SEARCH OUR NEW PUBS; WHICH WERE ISSUED ON APR/THU/04; FOR ANY PROC THAT APPLIED. HOWEVER; NONE EXISTED. BOTH STARTS WERE NORMAL AND THE AFTER FLOW WAS BEGUN. THE GND CREW WAS CLRED TO DISCONNECT ELECTRICAL PWR AND THE GND START UNIT. I WAS CHKING ENG INSTS WHEN I FIRST PERCEIVED MOVEMENT. AT THE SAME TIME THE FO WAS ACCOMPLISHING THE AFTER START CHKLIST; HE NOTICED MOVEMENT AND STATED 'BRAKES; BRAKES.' THE ACFT MOVED FORWARD WHAT WE THOUGHT WAS APPROX 5 FT BEFORE I COULD STOP MOVEMENT WITH BRAKES. THE TUG WAS PUSHED BACK AND HAD MOVED A FEW FT L OF THE CTRLINE AS WE CAME TO A STOP. I COMMUNICATED WITH BOTH THE TUG DRIVER AND THE FLT ATTENDANTS ABOUT THEIR SAFETY AND WHAT HAPPENED AND THE FO MADE A PA TO THE PAX. A MECH WAS ASKED TO LOOK/INSPECT THE ACFT AND TUG FOR DAMAGE. NONE WAS FOUND EXCEPT FOR A BROKEN SHEAR PIN ON THE TOW BAR. WE CONTINUED WITH THE FLT AND MADE AN INFO-ONLY WRITE-UP IN THE LOGBOOK. A PROC IN THE GND CREW GUIDANCE INSTRUCTS THEM TO COORD THE PARKING BRAKE POS WITH THE CHOCK REMOVAL AND STARTING ENGS. THIS WAS NEVER ACCOMPLISHED; SO THE CHOCKS WERE REMOVED AND THE BRAKES WERE NOT SET; ALLOWING THE ACFT TO MOVE FORWARD AFTER START. RECOMMEND MD88 SET BRAKES BEFORE ALL STARTS WHEN STATIONARY AND FOLLOW WRITTEN PROCS.