TXWY EXCURSION.

Narrative

OUR 737-300 WAS LANDED ON RWY 20 AT IDA BY THE CAPT. AFTER MAKING A COMPLETE STOP WE MADE A L TURN ONTO TXWY A-3 WHICH HAD PATCHY SNOW. AT A SLOW WALK SPD WE AGAIN MADE A L TURN. THROUGH ABOUT 45 DEGS OF THE TURN THE ACFT NO LONGER TURNED L BUT SLID R. THE CAPT IMMEDIATELY APPLIED BRAKES AND REVERSE THRUST; BUT THE LATTER DIDN'T RESPOND IN TIME DUE TO THE SLOW SPOOL-UP OF THE CFM-56 ENGS. THE ACFT CAME TO REST PARALLEL TO TXWY A WITH THE R MAIN AND NOSE GEAR WHEELS OFF THE TXWY IN THE SNOW. WE IMMEDIATELY SHUTDOWN THE ENGS; INFORMED THE PAX AND GND CTL. WE THEN REQUESTED A SANDING TRUCK TO BE ABLE TO GET OTHER VEHICLES OUT SAFELY TO AID US. UNFORTUNATELY GETTING A BUS FOR THE PAX TOOK AN EXCESSIVE AMOUNT OF TIME; 1 PLUS 30 MINS. A MECH LOOKED THE ACFT OVER AND DETERMINED IT WAS SAFE TO PULL IT OUT OF THE SNOW. A TUG AND TRACTOR PULLED THE ACFT OUT AND OVER TO THE GATE WHERE MAINT ONCE AGAIN CHKED OVER THE ACFT AND FOUND NO DAMAGE. MAINT CTL WAS CONSULTED THROUGHOUT THIS PROCESS AND WE FLEW THE ACFT TO SLC. WE WERE TOLD THERE HAD BEEN PRECIPITATION EARLIER IN THE AFTERNOON AND ON LNDG THE TEMP WAS 26 DEGS; WHICH PROBABLY LED TO BLACK ICE FORMING ON THE TXWY. THE AREA HAD BEEN CHKED AN HR BEFORE OUR LNDG AND WAS CLR. NO OTHER ACFT HAD USED THE TXWY SINCE THAT CHK. I REALIZE IT IS UNFEASIBLE TO CHK THE TXWYS BEFORE EACH PLANE LANDS. POSSIBLY MORE ATTN COULD BE DIRECTED TO THE TXWY THAT LEADS DIRECTLY INTO THE RAMP FROM THE RWY AND HAVE ACFT BACK-TAXI TO IT IF PRECIPITATION AND FREEZING TEMPS OCCUR PRIOR TO ARR TIME.