What was found
DURING FLIGHT 3148, F/O'S AIRSPEED INDICATOR BEGAN INDICATING OVER 250 KNOTS, AND KEPT CLIMBING IN 16,000 FT. CAPTS AND STBY INDICATED 210 KNOTS. AIR RETURN TO MSP. MAINTENANCE DRAINED AND PURGED NR 2 PITOT SYSTEM WITH NITROGEN. CLEANED DEBRIS FROM NR 2 PITOT TUBE, DRAIN NR 2 PITOT/STATIC SYSTEM. OPS AND LEAK CHECKS GOOD. IAW SF340 MM CHAP 34, ALSO INSPECTED STBY AND NR 1 PITOT DRAINS FOR MOISTURE. NO DEFECTS NOTED.