RWY EXCURSION - OFF RWY.

Narrative

A NORMAL LNDG AND SLOWING OF THE ACFT TO DEPART THE PLANNED TXWY WAS ACCOMPLISHED. BRAKING ACTION DURING THIS TIME WAS GOOD. PRIOR TO DEPARTING THE RWY FOR THE PLANNED DEP TXWY THE TWR TOLD US TO GO TO THE END AND TAKE A L WHICH APPEARED TO BE ABOUT 2000 FT. AT THIS TIME I STOWED THE THRUST REVERSERS AND ADVANCED THE THROTTLES TO KEEP THE ACFT MOVING TOWARD THE RWY END ON CTRLINE. TAKING THE WET RWY CONDITIONS INTO CONSIDERATION; I APPLIED THE BRAKES AGAIN AT A POINT I PERCEIVED TO BE A SAFE DISTANCE TO SLOW TO TAXI SPD TO DEPART THE RWY. BRAKING ACTION WAS GOOD FOR A SHORT PERIOD OF TIME AND THEN NO BRAKING ACTION AT ALL; THE ACFT STARTED SLIDING FORWARD. I WAS ABLE TO EASE THE ACFT TO THE L OF CTRLINE BUT STILL NO BRAKING ACTION. IT WAS INEVITABLE THAT THE ACFT WOULD NOT BE STOPPED ON THE RWY; SO I TRIED TO DIRECT IT AT A POINT FOR CREW SAFETY AND TO NOT CAUSE ANY DAMAGE TO THE ACFT OR RWY LIGHTING. THE ACFT DEPARTED THE L SIDE OF THE RWY INTO THE GRASS. CONTRIBUTING FACTORS TO NO BRAKING ACTION AND SLIDING WAS DUE TO THE RWY CONDITIONS (ESPECIALLY PAINTED AREAS) IN THE TOUCHDOWN AREA; WHICH WAS LATER CONFIRMED BY THE PEOPLE MOVING THE ACFT. OUR OPERATING PROCS STATE THAT THE THRUST REVERSERS SHOULD BE LEFT IN THE REVERSE IDLE POS UNTIL A SAFE TAXI SPD CAN BE ACCOMPLISHED; WHICH WAS DONE PRIOR TO THE PLANNED DEP TXWY. EVEN THOUGH THE THRUST REVERSERS; ON THESE ENGS; ARE NOT VERY EFFECTIVE BELOW 60 KTS; HAD I JUST RETURNED THE THRUST REVERSERS TO THE IDLE DETENT POS I COULD HAVE PLACED THEM IN FULL REVERSE. BUT; IN MY OPINION; CONSIDERING THE SPOOL UP TIME ON THE CFM-56; HAD I PLACED THEM IN FULL REVERSE THE OUTCOME WOULD NOT HAVE CHANGED AND I COULD HAVE DAMAGED 4 GOOD ENGS DUE TO FOREIGN OBJECT DAMAGE INGESTION.