A DC10-30 SLIDES OFF OF ICE COVERED CARGO RAMP AT DTW DURING A NIGHT TAXI OP.

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L MAIN TRUCK DEPARTED RAMP APRON WHILE ATTEMPTING TO TURN ONTO TXWY Z OUT OF CARGO RAMP. CONDITIONS AT THE TIME WERE NIGHT; MODERATE SNOW; 6 INCHES ON THE GND AND TXWYS (NOT PLOWED). WIND GUSTING TO +20 KTS; RVR 5000 FT. IN DTW; WE HAVE A TIGHT RAMP WITH AN UPHILL EXIT TO TXWY Z. ACFT HAD JUST BEEN DEICED. HAD HOLDOVER TIME OF 30 MINS AT THE START OF TAXI; ONLY HAD ABOUT 18 MINS OF HOLDOVER TIME LEFT. PUSHBACK POS LEFT US HDG 030 DEGS ON OUR RAMP. TAXI INSTRUCTIONS WERE TO GO SBOUND ON TXWY Z; HOLD SHORT OF TXWY V. THIS WOULD REQUIRE AN IMMEDIATE 90 DEG R TURN; FOLLOWED SHORTLY BY ANOTHER IMMEDIATE 90 DEG R TURN ONTO TXWY Z. BECAUSE OF THE ACFT SIZE; I HAVE TO ENSURE I DON'T 'SHORT' THE INSIDE OF THE TURN; OTHERWISE THE INBOUND TRUCK WOULD COME CLOSE TO OR OFF THE TXWY. KNOWING THIS; I HAVE TO TAXI FORWARD AND SQUARE THE TURNS. AT A SPD OF 4 KTS; STARTED FIRST TURN. AFTER 40 DEGS OF TURN; NOSE TIRE STARTED SKIDDING STRAIGHT; BRINGING THE ACFT PAST MY INITIAL TURN POINT. I WAS ABOUT TO ABORT THE TAXI WHEN THE NOSE TIRE CAUGHT AGAIN AND WE TURNED ANOTHER 50 DEGS. I KNEW I WAS DANGEROUSLY CLOSE TO THE L EDGE SO I ATTEMPTED TO CONTINUE TURNING. NOSE TIRE SKIDDED AGAIN STRAIGHT FORWARD. L MAIN TIRES JUST LEFT THE PAVEMENT LEAVING US STUCK WITH OUR NOSE 1/4 OF THE WAY INTO TXWY Z. AFTER THE FACT IT'S OBVIOUS I SHOULD HAVE STAYED WITH MY INITIAL DECISION TO ABORT THE TAXI. COULD HAVE HAD MAINT PUSH US ONTO TXWY Z. FACTORS INFLUENCING MY DECISION: MAINT HAD TO DEICE AN AIRBUS AFTER PUSHING US BACK. I KNEW WITH MY LIMITED REMAINING HOLDOVER TIME; IF THEY HOOKED UP AGAIN; I WOULD HAVE TO GO THROUGH DEICING/ANTI-ICING AGAIN -- FURTHER ADDING TO OUR DELAY. SUPPLEMENTAL INFO FROM ACN 430442: WX CONDITIONS WERE VERY BAD. BLOWING SNOW; VISIBILITY BELOW 1/2 MI; RVR OF 5000 FT OR LESS; 30-20 KTS OF WIND BLOWING 90 DEGS TO ACFT TAXI DIRECTION. NOSEWHEEL WAS BALD AND DID NOT GRAB VERY WELL ON THE ICE AND SNOW. IN MY OPINION; THE SIT WAS CAUSED BY ICY RAMP AND THE ACFT WX VANING IN THE TURN. CORRECTIVE ACTION: NEXT TIME USE THE TUG TO GET ON THE TXWY.