LTT CPR JET SKIDDED OFF THE SIDE OF THE RWY AFTER LNDG DUE TO 'BLACK ICE.'

Narrative

ON TOUCHDOWN ON RWY 30L AT CPS; ACFT IMMEDIATELY SKID OFF L SIDE OF RWY IN ABOUT A 20 DEG R YAW. DEPARTED RWY ABOUT 1500 FT DOWN AND SKID 2500 FT PARALLEL TO RWY AND THEN GOT ACFT BACK ON RWY. NO PERSONS WERE INJURED AND ONLY MINOR DAMAGE TO ACFT. TEMP AT TIME OF LNDG WAS RPTED ABOUT 35 DEGS; HOWEVER IT WAS FOUND OUT LATER THAT LOW GND TEMPS WERE AT FREEZING. DEWPOINT TEMP SPREAD 1 DEG; WIND 4 KTS; QUARTERING TAILWIND; SNOW AND ICE HAD BEEN REMOVED FROM ACTIVE RWY SEVERAL DAYS BEFORE BUT REMAINED IN LOW PILES AT SIDES OF RWY. ATIS WAS RPTING BRAKING ACTION ON UNUSED RWY BUT NO BRAKING ACTION WAS GIVEN ON ACTIVE RWY LEADING US TO BELIEVE BRAKING ACTION GOOD. WE LATER FOUND OUT THAT BRAKING ACTION HAD NOT BEEN TESTED FOR AT LEAST 3 HRS PRIOR TO OUR LNDG. WE ALSO HAD HEARD FROM THE LINEMAN WHEN WE PARKED THAT A LEARJET HAD LANDED PRIOR TO US AND HAD A 'WILD RIDE' AND SKID SIDEWAYS ON RWYS. I GUESS THE LEAR DID NOT RPT THIS TO TWR AND THE TWR COULD NOT SEE THE RWY DUE TO FOG; SO WE DID NOT HAVE THIS INFO ON LNDG. MY GUESS IS THAT WE HIT BLACK ICE. IT HAPPENED SO FAST THERE WAS NOTHING WE COULD DO TO CTL IT UNTIL THE ACFT LEFT THE RWY. AFTER WE GOT IN THE GRASS WE PARALLELED THE RWY UNTIL WE SLOWED DOWN AND THEN STEERED AIRPLANE ONTO RWY.