A310 CREW SLID OFF RAMP DURING A SNOWSTORM

Narrative

AS WE TAXIED INTO OUR RAMP THE WX WAS CHANGING FROM LIGHT SNOW TO HVY SNOW. WE STOPPED IN THE THROAT OF THE APRON TO ALLOW ANOTHER ACFT TO PARK. UNTIL THIS POINT WE HAD NO PROBS WITH BRAKING ACTION OR LOSS OF FRICTION DURING THE TURNS. AS WE WAITED; THE CONDITION OF THE RAMP WORSENED MAKING MARKINGS HARD TO SEE AND THE EDGE OF THE RAMP ALMOST INDISTINGUISHABLE. WE COULD SEE THE CTRLINE WELL ENOUGH TO TAXI AND DID NOT HAVE ANY REASON TO BELIEVE THAT THE RAMP WAS SLIPPERY. AS I PUSHED THE PWR UP AND STARTED TO MOVE AT ABOUT 2-3 KIAS. THE ACFT STARTED TO MOVE. WE APPLIED NOSEWHEEL STEERING TO MAKE A R TURN. AS WE DID THE ACFT WENT INTO A SLIDE TO THE R. I IMMEDIATELY PULLED THE PWR BACK; CTRED THE TILLER AND SMOOTHLY APPLIED THE BRAKES. THE ACFT CONTINUED TO SLIDE FOR ABOUT 10 FT AND THE R MAIN GEAR LEFT THE CONCRETE. THERE WAS NO DAMAGE TO THE ACFT OR ANY PERSONNEL. THIS WAS ON A COMPANY RAMP IN THE NON MOVEMENT AREA OF THE ARPT. A MEDIATED FLT SAFETY BRIEFING WAS CONDUCTED AT THE COMPANY WITH FLT SAFETY AND THE STANDARDS DEPT TO DISCUSS THE FACTORS THAT CONTRIBUTED TO THIS SIT AND A COMPANY LINE CHK WILL FOLLOW.