What was found
AIRCRAFT WAS GROUNDED: AT APPROXIMATELY 16000 FEET IN THE CLIMB "AIRSPEED" DISAGREE ILLUMINATED ON BOTH PRIMARY FLIGHT DISPLAY'S. DETERMINED CAPTAIN'S AIR SPEED WAS UNRELIABLE AND FIRST OFFICER'S AND STANDBY AIRSPEED AGREED WITH EACH OTHER AND GROUND SPEED AS WE RUN QUICK REFERENCE CARD PLUS QUICK REFERENCE HANDBOOK CHECK LISTS, CONTINUED CLIMB AND CAPTAIN'S AIRSPEED INDICATOR CONTINUED DEVIATING TO APPROXIMATELY 18 KNOTS COMPARED TO FIRST OFFICER'S AND INTEGRATED STANDBY FLIGHT DISPLAY'S ENGINE INSTRUMENTS WENT TO DASHES AND RETURNED AS WE DESCENDED AND NORMALIZED TO EACH OTHER THE LOWER WE DESCENDED. REMOVED AND REPLACED LEFT AIR DATA MODULE PER AMM 34-21-04 (PITOT MODULE).