What was found
DURING CRUISE, AT FL 230 NOTICED A/S SPLIT BETWEEN STANDBY ATT INDICATOR AIRSPEED AND PILOT'S & CO-PILOT'S AIRSPEED. BOTH PFD'S SHOWED 240 KNOTS, STANDBY SHOWED 271 KNOTS. SPLIT DECREASED WITH ALTITUDE, ALL INDICATIONS MATCHED AT 8000'. ON FINAL APPROACH, PFD 1 & 2 SHOWED AIRSPEEDS APROXIMATELY 5-6 KNOTS FASTER THAN STANDBY AIRSPEED. DIVERTED AND ACCOMPLISHED UNEVENTFUL LANDING. REMOVED ISI, INSPECTED TUBING. FOUND PITOT FLEX LINE CHAFED BETWEEN BEHIND INSTRUMENT. R & R PITOT LINE, COMPLIED WITH NITROGEN PURGE OF ALL PITOT AND STATIC LINES AND COMPLIED WITH PITOT STATIC LEAK CHECK IAW MM 34-12-16-000-801, 34-12-16-400-801, & 34-11-00-170-801. OPS CHECKED GOOD. RETURNED TO SERVICE.